add sliver.

Assets/UIWidgets/painting/basic_types.cs

 using System;
 using System.ComponentModel;
+using UIWidgets.ui;
 
 namespace UIWidgets.painting {
     public enum AxisDirection {
         up,
         down,
     }
-    
+
     public static class AxisUtils {
         public static Axis flipAxis(Axis direction) {
             switch (direction) {
                     return Axis.horizontal;
             }
-            
+
-        
+
         public static Axis axisDirectionToAxis(AxisDirection axisDirection) {
             switch (axisDirection) {
                 case AxisDirection.up:
                 case AxisDirection.right:
                     return Axis.horizontal;
+            }
+
+            throw new Exception("unknown axisDirection");
+        }
+
+        public static AxisDirection textDirectionToAxisDirection(TextDirection textDirection) {
+            switch (textDirection) {
+                case TextDirection.rtl:
+                    return AxisDirection.left;
+                case TextDirection.ltr:
+                    return AxisDirection.right;
+            }
+
+            throw new Exception("unknown textDirection");
+        }
+
+        public static AxisDirection flipAxisDirection(AxisDirection axisDirection) {
+            switch (axisDirection) {
+                case AxisDirection.up:
+                    return AxisDirection.down;
+                case AxisDirection.right:
+                    return AxisDirection.left;
+                case AxisDirection.down:
+                    return AxisDirection.up;
+                case AxisDirection.left:
+                    return AxisDirection.right;
+            }
+
+            throw new Exception("unknown axisDirection");
+        }
+
+        public static bool axisDirectionIsReversed(AxisDirection axisDirection) {
+            switch (axisDirection) {
+                case AxisDirection.up:
+                case AxisDirection.left:
+                    return true;
+                case AxisDirection.down:
+                case AxisDirection.right:
+                    return false;
             }
 
             throw new Exception("unknown axisDirection");

Assets/UIWidgets/rendering/object.mixin.gen.cs

     }
 
 
+    public abstract class RenderObjectWithChildMixinRenderSliver<ChildType> : RenderSliver where ChildType : RenderObject {
+        public ChildType _child;
+
+        public ChildType child {
+            get { return this._child; }
+            set {
+                if (this._child != null) {
+                    this.dropChild(this._child);
+                }
+
+                this._child = value;
+                if (this._child != null) {
+                    this.adoptChild(this._child);
+                }
+            }
+        }
+
+        public override void attach(object owner) {
+            base.attach(owner);
+            if (this._child != null) {
+                this._child.attach(owner);
+            }
+        }
+
+        public override void detach() {
+            base.detach();
+            if (this._child != null) {
+                this._child.detach();
+            }
+        }
+
+        public override void redepthChildren() {
+            if (this._child != null) {
+                this.redepthChild(this._child);
+            }
+        }
+
+        public override void visitChildren(RenderObjectVisitor visitor) {
+            if (this._child != null) {
+                visitor(this._child);
+            }
+        }
+    }
+
 
 
     public abstract class ContainerParentDataMixinParentData<ChildType> : ParentData, ContainerParentDataMixin<ChildType> where ChildType : RenderObject {
 
 
 
+    public abstract class ContainerParentDataMixinSliverPhysicalParentData<ChildType> : SliverPhysicalParentData, ContainerParentDataMixin<ChildType> where ChildType : RenderObject {
+        public ChildType previousSibling { get; set; }
+
+        public ChildType nextSibling { get; set; }
+
+        public override void detach() {
+            base.detach();
+
+            if (this.previousSibling != null) {
+                var previousSiblingParentData = (ContainerParentDataMixin<ChildType>) this.previousSibling.parentData;
+                previousSiblingParentData.nextSibling = this.nextSibling;
+            }
+
+            if (this.nextSibling != null) {
+                var nextSiblingParentData = (ContainerParentDataMixin<ChildType>) this.nextSibling.parentData;
+                nextSiblingParentData.previousSibling = this.previousSibling;
+            }
+
+            this.previousSibling = null;
+            this.nextSibling = null;
+        }
+    }
+
+
+
+    public abstract class ContainerParentDataMixinSliverLogicalParentData<ChildType> : SliverLogicalParentData, ContainerParentDataMixin<ChildType> where ChildType : RenderObject {
+        public ChildType previousSibling { get; set; }
+
+        public ChildType nextSibling { get; set; }
+
+        public override void detach() {
+            base.detach();
+
+            if (this.previousSibling != null) {
+                var previousSiblingParentData = (ContainerParentDataMixin<ChildType>) this.previousSibling.parentData;
+                previousSiblingParentData.nextSibling = this.nextSibling;
+            }
+
+            if (this.nextSibling != null) {
+                var nextSiblingParentData = (ContainerParentDataMixin<ChildType>) this.nextSibling.parentData;
+                nextSiblingParentData.previousSibling = this.previousSibling;
+            }
+
+            this.previousSibling = null;
+            this.nextSibling = null;
+        }
+    }
+
+
+
 
 
     public abstract class ContainerRenderObjectMixinRenderBox<ChildType, ParentDataType> : RenderBox
         public int _childCount = 0;
 
-        public int countCount {
+        public int childCount {
             get { return this._childCount; }
         }
 
 
         public int _childCount = 0;
 
-        public int countCount {
+        public int childCount {
             get { return this._childCount; }
         }
 

Assets/UIWidgets/rendering/object.mixin.njk

 
 {{ RenderObjectWithChildMixin('RenderBox') }}
 
+{{ RenderObjectWithChildMixin('RenderSliver') }}
 
 {% macro ContainerParentDataMixin(with) %}
     public abstract class ContainerParentDataMixin{{with}}<ChildType> : {{with}}, ContainerParentDataMixin<ChildType> where ChildType : RenderObject {
 
 {{ ContainerParentDataMixin('BoxParentData') }}
 
+{{ ContainerParentDataMixin('SliverPhysicalParentData') }}
+
+{{ ContainerParentDataMixin('SliverLogicalParentData') }}
+
 
 {% macro ContainerRenderObjectMixin(with) %}
     public abstract class ContainerRenderObjectMixin{{with}}<ChildType, ParentDataType> : {{with}}
         public int _childCount = 0;
 
-        public int countCount {
+        public int childCount {
             get { return this._childCount; }
         }
 

Assets/UIWidgets/rendering/sliver.cs

-namespace UIWidgets.rendering {
+using System;
+using UIWidgets.painting;
+using UIWidgets.ui;
+using UnityEngine;
+using Rect = UIWidgets.ui.Rect;
+
+namespace UIWidgets.rendering {
+    public enum GrowthDirection {
+        forward,
+        reverse,
+    }
+
+    public static class GrowthDirectionUtils {
+        public static AxisDirection applyGrowthDirectionToAxisDirection(
+            AxisDirection axisDirection, GrowthDirection growthDirection) {
+            switch (growthDirection) {
+                case GrowthDirection.forward:
+                    return axisDirection;
+                case GrowthDirection.reverse:
+                    return AxisUtils.flipAxisDirection(axisDirection);
+            }
+
+            throw new Exception("unknown growthDirection");
+        }
+
+        public static ScrollDirection applyGrowthDirectionToScrollDirection(
+            ScrollDirection scrollDirection, GrowthDirection growthDirection) {
+            switch (growthDirection) {
+                case GrowthDirection.forward:
+                    return scrollDirection;
+                case GrowthDirection.reverse:
+                    return ScrollDirectionUtils.flipScrollDirection(scrollDirection);
+            }
-    public class SliverPhysicalParentData : ContainerParentDataMixinParentData<RenderSliver> {
+            throw new Exception("unknown growthDirection");
+        }
-    public class SliverPhysicalContainerParentData : SliverPhysicalParentData {
+    public class SliverConstraints : Constraints, IEquatable<SliverConstraints> {
+        public SliverConstraints(
+            AxisDirection axisDirection,
+            GrowthDirection growthDirection,
+            ScrollDirection userScrollDirection,
+            double scrollOffset,
+            double overlap,
+            double remainingPaintExtent,
+            double crossAxisExtent,
+            AxisDirection crossAxisDirection,
+            double viewportMainAxisExtent,
+            double remainingCacheExtent,
+            double cacheOrigin
+        ) {
+            this.axisDirection = axisDirection;
+            this.growthDirection = growthDirection;
+            this.userScrollDirection = userScrollDirection;
+            this.scrollOffset = scrollOffset;
+            this.overlap = overlap;
+            this.remainingPaintExtent = remainingPaintExtent;
+            this.crossAxisExtent = crossAxisExtent;
+            this.crossAxisDirection = crossAxisDirection;
+            this.viewportMainAxisExtent = viewportMainAxisExtent;
+            this.remainingCacheExtent = remainingCacheExtent;
+            this.cacheOrigin = cacheOrigin;
+        }
+
+        public SliverConstraints copyWith(
+            AxisDirection? axisDirection = null,
+            GrowthDirection? growthDirection = null,
+            ScrollDirection? userScrollDirection = null,
+            double? scrollOffset = null,
+            double? overlap = null,
+            double? remainingPaintExtent = null,
+            double? crossAxisExtent = null,
+            AxisDirection? crossAxisDirection = null,
+            double? viewportMainAxisExtent = null,
+            double? remainingCacheExtent = null,
+            double? cacheOrigin = null
+        ) {
+            return new SliverConstraints(
+                axisDirection: axisDirection ?? this.axisDirection,
+                growthDirection: growthDirection ?? this.growthDirection,
+                userScrollDirection: userScrollDirection ?? this.userScrollDirection,
+                scrollOffset: scrollOffset ?? this.scrollOffset,
+                overlap: overlap ?? this.overlap,
+                remainingPaintExtent: remainingPaintExtent ?? this.remainingPaintExtent,
+                crossAxisExtent: crossAxisExtent ?? this.crossAxisExtent,
+                crossAxisDirection: crossAxisDirection ?? this.crossAxisDirection,
+                viewportMainAxisExtent: viewportMainAxisExtent ?? this.viewportMainAxisExtent,
+                remainingCacheExtent: remainingCacheExtent ?? this.remainingCacheExtent,
+                cacheOrigin: cacheOrigin ?? this.cacheOrigin
+            );
+        }
+
+        public readonly AxisDirection axisDirection;
+
+        public readonly GrowthDirection growthDirection;
+
+        public readonly ScrollDirection userScrollDirection;
+
+        public readonly double scrollOffset;
+
+        public readonly double overlap;
+
+        public readonly double remainingPaintExtent;
+
+        public readonly double crossAxisExtent;
+
+        public readonly AxisDirection crossAxisDirection;
+
+        public readonly double viewportMainAxisExtent;
+
+        public readonly double cacheOrigin;
+
+        public readonly double remainingCacheExtent;
+
+        public Axis axis {
+            get { return AxisUtils.axisDirectionToAxis(this.axisDirection); }
+        }
+
+        public GrowthDirection normalizedGrowthDirection {
+            get {
+                switch (this.axisDirection) {
+                    case AxisDirection.down:
+                    case AxisDirection.right:
+                        return this.growthDirection;
+                    case AxisDirection.up:
+                    case AxisDirection.left:
+                        switch (this.growthDirection) {
+                            case GrowthDirection.forward:
+                                return GrowthDirection.reverse;
+                            case GrowthDirection.reverse:
+                                return GrowthDirection.forward;
+                        }
+
+                        throw new Exception("unknown growthDirection");
+                }
+
+                throw new Exception("unknown axisDirection");
+            }
+        }
+
+        public override bool isTight {
+            get { return false; }
+        }
+
+        public override bool isNormalized {
+            get {
+                return this.scrollOffset >= 0.0
+                       && this.crossAxisExtent >= 0.0
+                       && AxisUtils.axisDirectionToAxis(this.axisDirection) !=
+                       AxisUtils.axisDirectionToAxis(this.crossAxisDirection)
+                       && this.viewportMainAxisExtent >= 0.0
+                       && this.remainingPaintExtent >= 0.0;
+            }
+        }
+
+        public BoxConstraints asBoxConstraints(
+            double minExtent = 0.0,
+            double maxExtent = double.PositiveInfinity,
+            double? crossAxisExtent = null
+        ) {
+            crossAxisExtent = crossAxisExtent ?? this.crossAxisExtent;
+            switch (this.axis) {
+                case Axis.horizontal:
+                    return new BoxConstraints(
+                        minHeight: crossAxisExtent.Value,
+                        maxHeight: crossAxisExtent.Value,
+                        minWidth: minExtent,
+                        maxWidth: maxExtent
+                    );
+                case Axis.vertical:
+                    return new BoxConstraints(
+                        minWidth: crossAxisExtent.Value,
+                        maxWidth: crossAxisExtent.Value,
+                        minHeight: minExtent,
+                        maxHeight: maxExtent
+                    );
+            }
+
+            return null;
+        }
+
+        public bool Equals(SliverConstraints other) {
+            if (object.ReferenceEquals(null, other)) return false;
+            if (object.ReferenceEquals(this, other)) return true;
+            return this.axisDirection == other.axisDirection
+                   && this.growthDirection == other.growthDirection
+                   && this.userScrollDirection == other.userScrollDirection
+                   && this.scrollOffset.Equals(other.scrollOffset)
+                   && this.overlap.Equals(other.overlap)
+                   && this.remainingPaintExtent.Equals(other.remainingPaintExtent)
+                   && this.crossAxisExtent.Equals(other.crossAxisExtent)
+                   && this.crossAxisDirection == other.crossAxisDirection
+                   && this.viewportMainAxisExtent.Equals(other.viewportMainAxisExtent)
+                   && this.cacheOrigin.Equals(other.cacheOrigin)
+                   && this.remainingCacheExtent.Equals(other.remainingCacheExtent);
+        }
+
+        public override bool Equals(object obj) {
+            if (object.ReferenceEquals(null, obj)) return false;
+            if (object.ReferenceEquals(this, obj)) return true;
+            if (obj.GetType() != this.GetType()) return false;
+            return this.Equals((SliverConstraints) obj);
+        }
+
+        public override int GetHashCode() {
+            unchecked {
+                var hashCode = (int) this.axisDirection;
+                hashCode = (hashCode * 397) ^ (int) this.growthDirection;
+                hashCode = (hashCode * 397) ^ (int) this.userScrollDirection;
+                hashCode = (hashCode * 397) ^ this.scrollOffset.GetHashCode();
+                hashCode = (hashCode * 397) ^ this.overlap.GetHashCode();
+                hashCode = (hashCode * 397) ^ this.remainingPaintExtent.GetHashCode();
+                hashCode = (hashCode * 397) ^ this.crossAxisExtent.GetHashCode();
+                hashCode = (hashCode * 397) ^ (int) this.crossAxisDirection;
+                hashCode = (hashCode * 397) ^ this.viewportMainAxisExtent.GetHashCode();
+                hashCode = (hashCode * 397) ^ this.cacheOrigin.GetHashCode();
+                hashCode = (hashCode * 397) ^ this.remainingCacheExtent.GetHashCode();
+                return hashCode;
+            }
+        }
+
+        public static bool operator ==(SliverConstraints left, SliverConstraints right) {
+            return Equals(left, right);
+        }
+
+        public static bool operator !=(SliverConstraints left, SliverConstraints right) {
+            return !Equals(left, right);
+        }
-    
+
+    public class SliverGeometry {
+        public SliverGeometry(
+            double scrollExtent = 0.0,
+            double paintExtent = 0.0,
+            double paintOrigin = 0.0,
+            double? layoutExtent = null,
+            double maxPaintExtent = 0.0,
+            double maxScrollObstructionExtent = 0.0,
+            double? hitTestExtent = null,
+            bool? visible = null,
+            bool hasVisualOverflow = false,
+            double scrollOffsetCorrection = 0.0,
+            double? cacheExtent = null
+        ) {
+            this.scrollExtent = scrollExtent;
+            this.paintExtent = paintExtent;
+            this.paintOrigin = paintOrigin;
+            this.layoutExtent = layoutExtent ?? paintExtent;
+            this.maxPaintExtent = maxPaintExtent;
+            this.maxScrollObstructionExtent = maxScrollObstructionExtent;
+            this.hitTestExtent = hitTestExtent ?? paintExtent;
+            this.visible = visible ?? paintExtent > 0.0;
+            this.hasVisualOverflow = hasVisualOverflow;
+            this.scrollOffsetCorrection = scrollOffsetCorrection;
+            this.cacheExtent = cacheExtent ?? layoutExtent ?? paintExtent;
+        }
+
+        public static readonly SliverGeometry zero = new SliverGeometry();
+
+        public readonly double scrollExtent;
+        public readonly double paintOrigin;
+        public readonly double paintExtent;
+        public readonly double layoutExtent;
+        public readonly double maxPaintExtent;
+        public readonly double maxScrollObstructionExtent;
+        public readonly double hitTestExtent;
+        public readonly bool visible;
+        public readonly bool hasVisualOverflow;
+        public readonly double scrollOffsetCorrection;
+        public readonly double cacheExtent;
+    }
+
+    public class SliverPhysicalParentData : ParentData {
+        public Offset paintOffset = Offset.zero;
+
+        public void applyPaintTransform(ref Matrix4x4 transform) {
+            transform = Matrix4x4.Translate(this.paintOffset.toVector()) * transform;
+        }
+    }
+
+    public class SliverPhysicalContainerParentData : ContainerParentDataMixinSliverPhysicalParentData<RenderSliver> {
+    }
+
+    public class SliverLogicalParentData : ParentData {
+        public double layoutOffset = 0.0;
+    }
+
+    public class SliverLogicalContainerParentData : ContainerParentDataMixinSliverLogicalParentData<RenderSliver> {
+    }
+
+
+        public new SliverConstraints constraints {
+            get { return (SliverConstraints) base.constraints; }
+        }
+
+        public SliverGeometry geometry {
+            get { return this._geometry; }
+            set { this._geometry = value; }
+        }
+
+        public SliverGeometry _geometry;
+
+        public override Rect paintBounds {
+            get {
+                switch (this.constraints.axis) {
+                    case Axis.horizontal:
+                        return Rect.fromLTWH(
+                            0.0, 0.0,
+                            this.geometry.paintExtent,
+                            this.constraints.crossAxisExtent
+                        );
+                    case Axis.vertical:
+                        return Rect.fromLTWH(
+                            0.0, 0.0,
+                            this.constraints.crossAxisExtent,
+                            this.geometry.paintExtent
+                        );
+                }
+
+                return null;
+            }
+        }
+
+        public override void performResize() {
+        }
+
+        public double centerOffsetAdjustment {
+            get { return 0.0; }
+        }
+
+        public double calculatePaintOffset(SliverConstraints constraints, double from, double to) {
+            double a = constraints.scrollOffset;
+            double b = constraints.scrollOffset + constraints.remainingPaintExtent;
+            return (to.clamp(a, b) - from.clamp(a, b)).clamp(0.0, constraints.remainingPaintExtent);
+        }
+
+        public double calculateCacheOffset(SliverConstraints constraints, double from, double to) {
+            double a = constraints.scrollOffset + constraints.cacheOrigin;
+            double b = constraints.scrollOffset + constraints.remainingCacheExtent;
+            return (to.clamp(a, b) - from.clamp(a, b)).clamp(0.0, constraints.remainingCacheExtent);
+        }
+
+        public virtual double childMainAxisPosition(RenderObject child) {
+            return 0.0;
+        }
+
+        public virtual double childCrossAxisPosition(RenderObject child) {
+            return 0.0;
+        }
+
+        public virtual double childScrollOffset(RenderObject child) {
+            return 0.0;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+        }
+
+        public Size getAbsoluteSizeRelativeToOrigin() {
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(
+                this.constraints.axisDirection, this.constraints.growthDirection)) {
+                case AxisDirection.up:
+                    return new Size(this.constraints.crossAxisExtent, -this.geometry.paintExtent);
+                case AxisDirection.right:
+                    return new Size(this.geometry.paintExtent, this.constraints.crossAxisExtent);
+                case AxisDirection.down:
+                    return new Size(this.constraints.crossAxisExtent, this.geometry.paintExtent);
+                case AxisDirection.left:
+                    return new Size(-this.geometry.paintExtent, this.constraints.crossAxisExtent);
+            }
+
+            return null;
+        }
+    }
+
+    public static class RenderSliverHelpers {
+        public static bool _getRightWayUp(SliverConstraints constraints) {
+            bool rightWayUp = true;
+            switch (constraints.axisDirection) {
+                case AxisDirection.up:
+                case AxisDirection.left:
+                    rightWayUp = false;
+                    break;
+                case AxisDirection.down:
+                case AxisDirection.right:
+                    rightWayUp = true;
+                    break;
+            }
+
+            switch (constraints.growthDirection) {
+                case GrowthDirection.forward:
+                    break;
+                case GrowthDirection.reverse:
+                    rightWayUp = !rightWayUp;
+                    break;
+            }
+
+            return rightWayUp;
+        }
+
+        public static void applyPaintTransformForBoxChild(this RenderSliver it, RenderBox child,
+            ref Matrix4x4 transform) {
+            bool rightWayUp = RenderSliverHelpers._getRightWayUp(it.constraints);
+            double delta = it.childMainAxisPosition(child);
+            double crossAxisDelta = it.childCrossAxisPosition(child);
+            switch (it.constraints.axis) {
+                case Axis.horizontal:
+                    if (!rightWayUp) {
+                        delta = it.geometry.paintExtent - child.size.width - delta;
+                    }
+
+                    transform = Matrix4x4.Translate(new Vector2((float) delta, (float) crossAxisDelta)) * transform;
+                    break;
+                case Axis.vertical:
+                    if (!rightWayUp) {
+                        delta = it.geometry.paintExtent - child.size.height - delta;
+                    }
+
+                    transform = Matrix4x4.Translate(new Vector2((float) crossAxisDelta, (float) delta)) * transform;
+                    break;
+            }
+        }
+    }
+
+    public abstract class RenderSliverSingleBoxAdapter : RenderObjectWithChildMixinRenderSliver<RenderBox> {
+        public RenderSliverSingleBoxAdapter(
+            RenderBox child = null
+        ) {
+            this.child = child;
+        }
+
+        public override void setupParentData(RenderObject child) {
+            if (!(child.parentData is SliverPhysicalParentData)) {
+                child.parentData = new SliverPhysicalParentData();
+            }
+        }
+
+        public void setChildParentData(RenderObject child, SliverConstraints constraints, SliverGeometry geometry) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(constraints.axisDirection,
+                constraints.growthDirection)) {
+                case AxisDirection.up:
+                    childParentData.paintOffset = new Offset(0.0,
+                        -(geometry.scrollExtent - (geometry.paintExtent + constraints.scrollOffset)));
+                    break;
+                case AxisDirection.right:
+                    childParentData.paintOffset = new Offset(-constraints.scrollOffset, 0.0);
+                    break;
+                case AxisDirection.down:
+                    childParentData.paintOffset = new Offset(0.0, -constraints.scrollOffset);
+                    break;
+                case AxisDirection.left:
+                    childParentData.paintOffset =
+                        new Offset(-(geometry.scrollExtent - (geometry.paintExtent + constraints.scrollOffset)), 0.0);
+                    break;
+            }
+        }
+
+        public override double childMainAxisPosition(RenderObject child) {
+            return -this.constraints.scrollOffset;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            childParentData.applyPaintTransform(ref transform);
+        }
+
+        public override void paint(PaintingContext context, Offset offset) {
+            if (this.child != null && this.geometry.visible) {
+                var childParentData = (SliverPhysicalParentData) this.child.parentData;
+                context.paintChild(this.child, offset + childParentData.paintOffset);
+            }
+        }
+    }
+
+    public class RenderSliverToBoxAdapter : RenderSliverSingleBoxAdapter {
+        public RenderSliverToBoxAdapter(
+            RenderBox child = null
+        ) : base(child) {
+        }
+
+        public override void performLayout() {
+            if (this.child == null) {
+                this.geometry = SliverGeometry.zero;
+                return;
+            }
+
+            this.child.layout(this.constraints.asBoxConstraints(), parentUsesSize: true);
+
+            double childExtent = 0.0;
+            switch (this.constraints.axis) {
+                case Axis.horizontal:
+                    childExtent = this.child.size.width;
+                    break;
+                case Axis.vertical:
+                    childExtent = this.child.size.height;
+                    break;
+            }
+
+            double paintedChildSize = this.calculatePaintOffset(this.constraints, from: 0.0, to: childExtent);
+            double cacheExtent = this.calculateCacheOffset(this.constraints, from: 0.0, to: childExtent);
+
+            this.geometry = new SliverGeometry(
+                scrollExtent: childExtent,
+                paintExtent: paintedChildSize,
+                cacheExtent: cacheExtent,
+                maxPaintExtent: childExtent,
+                hitTestExtent: paintedChildSize,
+                hasVisualOverflow: childExtent > this.constraints.remainingPaintExtent
+                                   || this.constraints.scrollOffset > 0.0
+            );
+
+            this.setChildParentData(this.child, this.constraints, this.geometry);
+        }
     }
 }

Assets/UIWidgets/rendering/viewpoint.cs

-using UIWidgets.painting;
+using System;
+using System.Collections.Generic;
+using UIWidgets.painting;
+using UIWidgets.ui;
 using UnityEngine;
 using Rect = UIWidgets.ui.Rect;
 
     public static class RenderAbstractViewportUtils {
         public static RenderAbstractViewport of(RenderObject obj) {
             while (obj != null) {
-                if (obj is RenderAbstractViewport)
+                if (obj is RenderAbstractViewport) {
+                }
+
                 obj = (RenderObject) obj.parent;
             }
 
         RenderAbstractViewport
         where ParentDataClass : ParentData, ContainerParentDataMixin<RenderSliver> {
         protected RenderViewportBase(
-            AxisDirection crossAxisDirection,
-            ViewportOffset offset,
-            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent,
-            AxisDirection axisDirection = AxisDirection.down
+            AxisDirection axisDirection = AxisDirection.down,
+            AxisDirection crossAxisDirection = AxisDirection.right,
+            ViewportOffset offset = null,
+            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent
-            Debug.Assert(AxisUtils.axisDirectionToAxis(axisDirection) !=
-                         AxisUtils.axisDirectionToAxis(crossAxisDirection));
             this._axisDirection = axisDirection;
             this._crossAxisDirection = crossAxisDirection;
             this._offset = offset;
         public Axis axis {
             get { return AxisUtils.axisDirectionToAxis(this.axisDirection); }
         }
-
 
         public ViewportOffset offset {
             get { return this._offset; }
             base.detach();
         }
 
+        public override double computeMinIntrinsicWidth(double height) {
+            return 0.0;
+        }
+
+        public override double computeMaxIntrinsicWidth(double height) {
+            return 0.0;
+        }
+
+        public override double computeMinIntrinsicHeight(double width) {
+            return 0.0;
+        }
+
+        public override double computeMaxIntrinsicHeight(double width) {
+            return 0.0;
+        }
+
+        public override bool isRepaintBoundary {
+            get { return true; }
+        }
+
+        public double layoutChildSequence(
+            RenderSliver child,
+            double scrollOffset,
+            double overlap,
+            double layoutOffset,
+            double remainingPaintExtent,
+            double mainAxisExtent,
+            double crossAxisExtent,
+            GrowthDirection growthDirection,
+            Func<RenderSliver, RenderSliver> advance,
+            double remainingCacheExtent,
+            double cacheOrigin
+        ) {
+            double initialLayoutOffset = layoutOffset;
+
+            ScrollDirection adjustedUserScrollDirection =
+                GrowthDirectionUtils.applyGrowthDirectionToScrollDirection(
+                    this.offset.userScrollDirection, growthDirection);
+
+            double maxPaintOffset = layoutOffset + overlap;
+
+            while (child != null) {
+                double sliverScrollOffset = scrollOffset <= 0.0 ? 0.0 : scrollOffset;
+                double correctedCacheOrigin = Math.Max(cacheOrigin, -sliverScrollOffset);
+                double cacheExtentCorrection = cacheOrigin - correctedCacheOrigin;
+
+                child.layout(new SliverConstraints(
+                    axisDirection: this.axisDirection,
+                    growthDirection: growthDirection,
+                    userScrollDirection: adjustedUserScrollDirection,
+                    scrollOffset: sliverScrollOffset,
+                    overlap: maxPaintOffset - layoutOffset,
+                    remainingPaintExtent: Math.Max(0.0, remainingPaintExtent - layoutOffset + initialLayoutOffset),
+                    crossAxisExtent: crossAxisExtent,
+                    crossAxisDirection: this.crossAxisDirection,
+                    viewportMainAxisExtent: mainAxisExtent,
+                    remainingCacheExtent: Math.Max(0.0, remainingCacheExtent + cacheExtentCorrection),
+                    cacheOrigin: correctedCacheOrigin
+                ), parentUsesSize: true);
+
+                var childLayoutGeometry = child.geometry;
+
+                if (childLayoutGeometry.scrollOffsetCorrection != 0.0) {
+                    return childLayoutGeometry.scrollOffsetCorrection;
+                }
+
+                double effectiveLayoutOffset = layoutOffset + childLayoutGeometry.paintOrigin;
+
+                if (childLayoutGeometry.visible || scrollOffset > 0) {
+                    this.updateChildLayoutOffset(child, effectiveLayoutOffset, growthDirection);
+                } else {
+                    this.updateChildLayoutOffset(child, -scrollOffset + initialLayoutOffset, growthDirection);
+                }
+
+                maxPaintOffset = Math.Max(effectiveLayoutOffset + childLayoutGeometry.paintExtent, maxPaintOffset);
+                scrollOffset -= childLayoutGeometry.scrollExtent;
+                layoutOffset += childLayoutGeometry.layoutExtent;
+
+                if (childLayoutGeometry.cacheExtent != 0.0) {
+                    remainingCacheExtent -= childLayoutGeometry.cacheExtent - cacheExtentCorrection;
+                    cacheOrigin = Math.Min(correctedCacheOrigin + childLayoutGeometry.cacheExtent, 0.0);
+                }
+
+                this.updateOutOfBandData(growthDirection, childLayoutGeometry);
+
+                child = advance(child);
+            }
+
+            return 0.0;
+        }
+
+        public override void paint(PaintingContext context, Offset offset) {
+            if (this.firstChild == null) {
+                return;
+            }
+
+            if (this.hasVisualOverflow) {
+                context.pushClipRect(this.needsCompositing, offset, Offset.zero & this.size, this._paintContents);
+            } else {
+                this._paintContents(context, offset);
+            }
+        }
+
+        public void _paintContents(PaintingContext context, Offset offset) {
+            foreach (RenderSliver child in this.childrenInPaintOrder) {
+                if (child.geometry.visible) {
+                    context.paintChild(child, offset + this.paintOffsetOf(child));
+                }
+            }
+        }
-            throw new System.NotImplementedException();
+            double leadingScrollOffset = 0.0;
+            double targetMainAxisExtent = 0.0;
+            RenderObject descendant;
+            rect = rect ?? target.paintBounds;
+
+            Matrix4x4 transform;
+
+            if (target is RenderBox) {
+                RenderBox targetBox = (RenderBox) target;
+
+                RenderBox pivot = targetBox;
+                while (pivot.parent is RenderBox) {
+                    pivot = (RenderBox) pivot.parent;
+                }
+
+                RenderSliver pivotParent = (RenderSliver) pivot.parent;
+
+                transform = targetBox.getTransformTo(pivot);
+                Rect bounds = MatrixUtils.transformRect(transform, rect);
+
+                double offset = 0.0;
+
+                GrowthDirection growthDirection = pivotParent.constraints.growthDirection;
+                switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(this.axisDirection, growthDirection)) {
+                    case AxisDirection.up:
+                        switch (growthDirection) {
+                            case GrowthDirection.forward:
+                                offset = bounds.bottom;
+                                break;
+                            case GrowthDirection.reverse:
+                                offset = bounds.top;
+                                break;
+                        }
+
+                        leadingScrollOffset = pivot.size.height - offset;
+                        targetMainAxisExtent = bounds.height;
+                        break;
+                    case AxisDirection.right:
+                        leadingScrollOffset = bounds.left;
+                        targetMainAxisExtent = bounds.width;
+                        break;
+                    case AxisDirection.down:
+                        leadingScrollOffset = bounds.top;
+                        targetMainAxisExtent = bounds.height;
+                        break;
+                    case AxisDirection.left:
+                        switch (growthDirection) {
+                            case GrowthDirection.forward:
+                                offset = bounds.right;
+                                break;
+                            case GrowthDirection.reverse:
+                                offset = bounds.left;
+                                break;
+                        }
+
+                        leadingScrollOffset = pivot.size.width - offset;
+                        targetMainAxisExtent = bounds.width;
+                        break;
+                }
+
+                descendant = pivot;
+            } else if (target is RenderSliver) {
+                RenderSliver targetSliver = (RenderSliver) target;
+                leadingScrollOffset = 0.0;
+                targetMainAxisExtent = targetSliver.geometry.scrollExtent;
+                descendant = targetSliver;
+            } else {
+                return new RevealedOffset(offset: this.offset.pixels, rect: rect);
+            }
+
+            RenderObject child = descendant;
+            while (child.parent is RenderSliver) {
+                var parent = (RenderSliver) child.parent;
+                leadingScrollOffset += parent.childScrollOffset(child);
+                child = parent;
+            }
+
+            RenderSliver sliver = (RenderSliver) child;
+            double extentOfPinnedSlivers = this.maxScrollObstructionExtentBefore(sliver);
+            leadingScrollOffset = this.scrollOffsetOf(sliver, leadingScrollOffset);
+            switch (sliver.constraints.growthDirection) {
+                case GrowthDirection.forward:
+                    leadingScrollOffset -= extentOfPinnedSlivers;
+                    break;
+                case GrowthDirection.reverse:
+                    break;
+            }
+
+            double mainAxisExtent = 0.0;
+            switch (this.axis) {
+                case Axis.horizontal:
+                    mainAxisExtent = this.size.width - extentOfPinnedSlivers;
+                    break;
+                case Axis.vertical:
+                    mainAxisExtent = this.size.height - extentOfPinnedSlivers;
+                    break;
+            }
+
+            double targetOffset = leadingScrollOffset - (mainAxisExtent - targetMainAxisExtent) * alignment;
+            double offsetDifference = this.offset.pixels - targetOffset;
+
+            transform = target.getTransformTo(this);
+            this.applyPaintTransform(child, ref transform);
+            Rect targetRect = MatrixUtils.transformRect(transform, rect);
+
+            switch (this.axisDirection) {
+                case AxisDirection.down:
+                    targetRect = targetRect.translate(0.0, offsetDifference);
+                    break;
+                case AxisDirection.right:
+                    targetRect = targetRect.translate(offsetDifference, 0.0);
+                    break;
+                case AxisDirection.up:
+                    targetRect = targetRect.translate(0.0, -offsetDifference);
+                    break;
+                case AxisDirection.left:
+                    targetRect = targetRect.translate(-offsetDifference, 0.0);
+                    break;
+            }
+
+            return new RevealedOffset(offset: targetOffset, rect: targetRect);
+
+        public Offset computeAbsolutePaintOffset(RenderSliver child, double layoutOffset,
+            GrowthDirection growthDirection) {
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(this.axisDirection, growthDirection)) {
+                case AxisDirection.up:
+                    return new Offset(0.0, this.size.height - (layoutOffset + child.geometry.paintExtent));
+                case AxisDirection.right:
+                    return new Offset(layoutOffset, 0.0);
+                case AxisDirection.down:
+                    return new Offset(0.0, layoutOffset);
+                case AxisDirection.left:
+                    return new Offset(this.size.width - (layoutOffset + child.geometry.paintExtent), 0.0);
+            }
+
+            return null;
+        }
+
+
+        public abstract bool hasVisualOverflow { get; }
+
+        public abstract void updateOutOfBandData(GrowthDirection growthDirection, SliverGeometry childLayoutGeometry);
+
+        public abstract void updateChildLayoutOffset(RenderSliver child, double layoutOffset,
+            GrowthDirection growthDirection);
+
+        public abstract Offset paintOffsetOf(RenderSliver child);
+
+        public abstract double scrollOffsetOf(RenderSliver child, double scrollOffsetWithinChild);
+
+        public abstract double maxScrollObstructionExtentBefore(RenderSliver child);
+
+        public abstract IEnumerable<RenderSliver> childrenInPaintOrder { get; }
-        public RenderViewport(AxisDirection crossAxisDirection, ViewportOffset offset,
-            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent,
-            AxisDirection axisDirection = AxisDirection.down) : base(crossAxisDirection, offset, cacheExtent,
-            axisDirection) {
+        public RenderViewport(
+            AxisDirection axisDirection = AxisDirection.down,
+            AxisDirection crossAxisDirection = AxisDirection.right,
+            ViewportOffset offset = null,
+            double anchor = 0.0,
+            List<RenderSliver> children = null,
+            RenderSliver center = null,
+            double cacheExtent = RenderAbstractViewportUtils.defaultCacheExtent
+        ) : base(axisDirection, crossAxisDirection, offset, cacheExtent) {
+            this.addAll(children);
+            if (center == null && this.firstChild != null) {
+                this._center = this.firstChild;
+            }
+        }
+
+        public override void setupParentData(RenderObject child) {
+            if (!(child.parentData is SliverPhysicalContainerParentData)) {
+                child.parentData = new SliverPhysicalContainerParentData();
+            }
+        }
+
+        public double anchor {
+            get { return this._anchor; }
+            set {
+                if (value != this._anchor) {
+                    return;
+                }
+
+                this._anchor = value;
+                this.markNeedsLayout();
+            }
+        }
+
+        public double _anchor;
+
+        public RenderSliver center {
+            get { return this._center; }
+            set {
+                if (value == this._center) {
+                    return;
+                }
+
+                this._center = value;
+                this.markNeedsLayout();
+            }
+        }
+
+        public RenderSliver _center;
+
+        public override bool sizedByParent {
+            get { return true; }
+        }
+
+        public override void performResize() {
+            this.size = this.constraints.biggest;
+
+            switch (this.axis) {
+                case Axis.vertical:
+                    this.offset.applyViewportDimension(this.size.height);
+                    break;
+                case Axis.horizontal:
+                    this.offset.applyViewportDimension(this.size.width);
+                    break;
+            }
+        }
+
+        public const int _maxLayoutCycles = 10;
+
+        public double _minScrollExtent;
+        public double _maxScrollExtent;
+        public bool _hasVisualOverflow = false;
+
+        public override void performLayout() {
+            if (this.center == null) {
+                this._minScrollExtent = 0.0;
+                this._maxScrollExtent = 0.0;
+                this._hasVisualOverflow = false;
+                this.offset.applyContentDimensions(0.0, 0.0);
+                return;
+            }
+
+            double mainAxisExtent = 0.0;
+            double crossAxisExtent = 0.0;
+            switch (this.axis) {
+                case Axis.vertical:
+                    mainAxisExtent = this.size.height;
+                    crossAxisExtent = this.size.width;
+                    break;
+                case Axis.horizontal:
+                    mainAxisExtent = this.size.width;
+                    crossAxisExtent = this.size.height;
+                    break;
+            }
+
+            double centerOffsetAdjustment = this.center.centerOffsetAdjustment;
+
+            int count = 0;
+            do {
+                var correction = this._attemptLayout(mainAxisExtent, crossAxisExtent,
+                    this.offset.pixels + centerOffsetAdjustment);
+                if (correction != 0.0) {
+                    this.offset.correctBy(correction);
+                } else {
+                    if (this.offset.applyContentDimensions(
+                        Math.Min(0.0, this._minScrollExtent + mainAxisExtent * this.anchor),
+                        Math.Max(0.0, this._maxScrollExtent - mainAxisExtent * (1.0 - this.anchor))
+                    ))
+                        break;
+                }
+
+                count += 1;
+            } while (count < RenderViewport._maxLayoutCycles);
+        }
+
+        public double _attemptLayout(double mainAxisExtent, double crossAxisExtent, double correctedOffset) {
+            this._minScrollExtent = 0.0;
+            this._maxScrollExtent = 0.0;
+            this._hasVisualOverflow = false;
+
+            double centerOffset = mainAxisExtent * this.anchor - correctedOffset;
+            double reverseDirectionRemainingPaintExtent = centerOffset.clamp(0.0, mainAxisExtent);
+            double forwardDirectionRemainingPaintExtent = (mainAxisExtent - centerOffset).clamp(0.0, mainAxisExtent);
+
+            double fullCacheExtent = mainAxisExtent + 2 * this.cacheExtent;
+            double centerCacheOffset = centerOffset + this.cacheExtent;
+            double reverseDirectionRemainingCacheExtent = centerCacheOffset.clamp(0.0, fullCacheExtent);
+            double forwardDirectionRemainingCacheExtent =
+                (fullCacheExtent - centerCacheOffset).clamp(0.0, fullCacheExtent);
+
+            RenderSliver leadingNegativeChild = this.childBefore(this.center);
+
+            if (leadingNegativeChild != null) {
+                double result = this.layoutChildSequence(
+                    child: leadingNegativeChild,
+                    scrollOffset: Math.Max(mainAxisExtent, centerOffset) - mainAxisExtent,
+                    overlap: 0.0,
+                    layoutOffset: forwardDirectionRemainingPaintExtent,
+                    remainingPaintExtent: reverseDirectionRemainingPaintExtent,
+                    mainAxisExtent: mainAxisExtent,
+                    crossAxisExtent: crossAxisExtent,
+                    growthDirection: GrowthDirection.reverse,
+                    advance: this.childBefore,
+                    remainingCacheExtent: reverseDirectionRemainingCacheExtent,
+                    cacheOrigin: (mainAxisExtent - centerOffset).clamp(-this.cacheExtent, 0.0)
+                );
+                if (result != 0.0) {
+                    return -result;
+                }
+            }
+
+            return this.layoutChildSequence(
+                child: this.center,
+                scrollOffset: Math.Max(0.0, -centerOffset),
+                overlap: leadingNegativeChild == null ? Math.Min(0.0, -centerOffset) : 0.0,
+                layoutOffset: centerOffset >= mainAxisExtent ? centerOffset : reverseDirectionRemainingPaintExtent,
+                remainingPaintExtent: forwardDirectionRemainingPaintExtent,
+                mainAxisExtent: mainAxisExtent,
+                crossAxisExtent: crossAxisExtent,
+                growthDirection: GrowthDirection.forward,
+                advance: this.childAfter,
+                remainingCacheExtent: forwardDirectionRemainingCacheExtent,
+                cacheOrigin: centerOffset.clamp(-this.cacheExtent, 0.0)
+            );
+        }
+
+        public override bool hasVisualOverflow {
+            get { return this._hasVisualOverflow; }
+        }
+
+        public override void updateOutOfBandData(GrowthDirection growthDirection, SliverGeometry childLayoutGeometry) {
+            switch (growthDirection) {
+                case GrowthDirection.forward:
+                    this._maxScrollExtent += childLayoutGeometry.scrollExtent;
+                    break;
+                case GrowthDirection.reverse:
+                    this._minScrollExtent -= childLayoutGeometry.scrollExtent;
+                    break;
+            }
+
+            if (childLayoutGeometry.hasVisualOverflow) {
+                this._hasVisualOverflow = true;
+            }
+        }
+
+        public override void updateChildLayoutOffset(RenderSliver child, double layoutOffset,
+            GrowthDirection growthDirection) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            childParentData.paintOffset = this.computeAbsolutePaintOffset(child, layoutOffset, growthDirection);
+        }
+
+        public override Offset paintOffsetOf(RenderSliver child) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            return childParentData.paintOffset;
+        }
+
+        public override double scrollOffsetOf(RenderSliver child, double scrollOffsetWithinChild) {
+            GrowthDirection growthDirection = child.constraints.growthDirection;
+            switch (growthDirection) {
+                case GrowthDirection.forward: {
+                    double scrollOffsetToChild = 0.0;
+                    RenderSliver current = this.center;
+                    while (current != child) {
+                        scrollOffsetToChild += current.geometry.scrollExtent;
+                        current = this.childAfter(current);
+                    }
+
+                    return scrollOffsetToChild + scrollOffsetWithinChild;
+                }
+                case GrowthDirection.reverse: {
+                    double scrollOffsetToChild = 0.0;
+                    RenderSliver current = this.childBefore(this.center);
+                    while (current != child) {
+                        scrollOffsetToChild -= current.geometry.scrollExtent;
+                        current = this.childBefore(current);
+                    }
+
+                    return scrollOffsetToChild - scrollOffsetWithinChild;
+                }
+            }
+
+            return 0.0;
+        }
+
+        public override double maxScrollObstructionExtentBefore(RenderSliver child) {
+            GrowthDirection growthDirection = child.constraints.growthDirection;
+            switch (growthDirection) {
+                case GrowthDirection.forward: {
+                    double pinnedExtent = 0.0;
+                    RenderSliver current = this.center;
+                    while (current != child) {
+                        pinnedExtent += current.geometry.maxScrollObstructionExtent;
+                        current = this.childAfter(current);
+                    }
+
+                    return pinnedExtent;
+                }
+                case GrowthDirection.reverse: {
+                    double pinnedExtent = 0.0;
+                    RenderSliver current = this.childBefore(this.center);
+                    while (current != child) {
+                        pinnedExtent += current.geometry.maxScrollObstructionExtent;
+                        current = this.childBefore(current);
+                    }
+
+                    return pinnedExtent;
+                }
+            }
+
+            return 0.0;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            childParentData.applyPaintTransform(ref transform);
+        }
+
+        public override IEnumerable<RenderSliver> childrenInPaintOrder {
+            get {
+                if (this.firstChild == null) {
+                    yield break;
+                }
+
+                var child = this.firstChild;
+                while (child != this.center) {
+                    yield return child;
+                    child = this.childAfter(child);
+                }
+
+                child = this.lastChild;
+                while (true) {
+                    yield return child;
+                    if (child == this.center) {
+                        yield break;
+                    }
+
+                    child = this.childBefore(child);
+                }
+            }
+        }
+    }
+
+    public class RenderShrinkWrappingViewport : RenderViewportBase<SliverLogicalContainerParentData> {
+        public RenderShrinkWrappingViewport(
+            AxisDirection axisDirection = AxisDirection.down,
+            AxisDirection crossAxisDirection = AxisDirection.right,
+            ViewportOffset offset = null,
+            List<RenderSliver> children = null
+        ) : base(
+            axisDirection: axisDirection,
+            crossAxisDirection: crossAxisDirection,
+            offset: offset) {
+            this.addAll(children);
+        }
+
+        public override void setupParentData(RenderObject child) {
+            if (!(child.parentData is SliverLogicalContainerParentData)) {
+                child.parentData = new SliverLogicalContainerParentData();
+            }
+        }
+
+        public double _maxScrollExtent = 0.0;
+        public double _shrinkWrapExtent = 0.0;
+        public bool _hasVisualOverflow = false;
+
+        public override void performLayout() {
+            if (this.firstChild == null) {
+                switch (this.axis) {
+                    case Axis.vertical:
+                        this.size = new Size(this.constraints.maxWidth, this.constraints.minHeight);
+                        break;
+                    case Axis.horizontal:
+                        this.size = new Size(this.constraints.minWidth, this.constraints.maxHeight);
+                        break;
+                }
+
+                this.offset.applyViewportDimension(0.0);
+                this._maxScrollExtent = 0.0;
+                this._shrinkWrapExtent = 0.0;
+                this._hasVisualOverflow = false;
+                this.offset.applyContentDimensions(0.0, 0.0);
+                return;
+            }
+
+            double mainAxisExtent = 0.0;
+            double crossAxisExtent = 0.0;
+            switch (this.axis) {
+                case Axis.vertical:
+                    mainAxisExtent = this.constraints.maxHeight;
+                    crossAxisExtent = this.constraints.maxWidth;
+                    break;
+                case Axis.horizontal:
+                    mainAxisExtent = this.constraints.maxWidth;
+                    crossAxisExtent = this.constraints.maxHeight;
+                    break;
+            }
+
+            double effectiveExtent = 0.0;
+            do {
+                var correction = this._attemptLayout(mainAxisExtent, crossAxisExtent, this.offset.pixels);
+                if (correction != 0.0) {
+                    this.offset.correctBy(correction);
+                } else {
+                    switch (this.axis) {
+                        case Axis.vertical:
+                            effectiveExtent = this.constraints.constrainHeight(this._shrinkWrapExtent);
+                            break;
+                        case Axis.horizontal:
+                            effectiveExtent = this.constraints.constrainWidth(this._shrinkWrapExtent);
+                            break;
+                    }
+
+                    bool didAcceptViewportDimension = this.offset.applyViewportDimension(effectiveExtent);
+                    bool didAcceptContentDimension =
+                        this.offset.applyContentDimensions(0.0, Math.Max(0.0, this._maxScrollExtent - effectiveExtent));
+                    if (didAcceptViewportDimension && didAcceptContentDimension) {
+                        break;
+                    }
+                }
+            } while (true);
+
+            switch (this.axis) {
+                case Axis.vertical:
+                    this.size = this.constraints.constrainDimensions(crossAxisExtent, effectiveExtent);
+                    break;
+                case Axis.horizontal:
+                    this.size = this.constraints.constrainDimensions(effectiveExtent, crossAxisExtent);
+                    break;
+            }
+        }
+
+        public double _attemptLayout(double mainAxisExtent, double crossAxisExtent, double correctedOffset) {
+            this._maxScrollExtent = 0.0;
+            this._shrinkWrapExtent = 0.0;
+            this._hasVisualOverflow = false;
+            return this.layoutChildSequence(
+                child: this.firstChild,
+                scrollOffset: Math.Max(0.0, correctedOffset),
+                overlap: Math.Min(0.0, correctedOffset),
+                layoutOffset: 0.0,
+                remainingPaintExtent: mainAxisExtent,
+                mainAxisExtent: mainAxisExtent,
+                crossAxisExtent: crossAxisExtent,
+                growthDirection: GrowthDirection.forward,
+                advance: this.childAfter,
+                remainingCacheExtent: mainAxisExtent + 2 * this.cacheExtent,
+                cacheOrigin: -this.cacheExtent
+            );
+        }
+
+        public override bool hasVisualOverflow {
+            get { return this._hasVisualOverflow; }
+        }
+
+        public override void updateOutOfBandData(GrowthDirection growthDirection, SliverGeometry childLayoutGeometry) {
+            this._maxScrollExtent += childLayoutGeometry.scrollExtent;
+            if (childLayoutGeometry.hasVisualOverflow) {
+                this._hasVisualOverflow = true;
+            }
+
+            this._shrinkWrapExtent += childLayoutGeometry.maxPaintExtent;
+        }
+
+        public override void updateChildLayoutOffset(RenderSliver child, double layoutOffset,
+            GrowthDirection growthDirection) {
+            var childParentData = (SliverLogicalParentData) child.parentData;
+            childParentData.layoutOffset = layoutOffset;
+        }
+
+        public override Offset paintOffsetOf(RenderSliver child) {
+            var childParentData = (SliverLogicalParentData) child.parentData;
+            return this.computeAbsolutePaintOffset(child, childParentData.layoutOffset, GrowthDirection.forward);
+        }
+
+        public override double scrollOffsetOf(RenderSliver child, double scrollOffsetWithinChild) {
+            double scrollOffsetToChild = 0.0;
+            RenderSliver current = this.firstChild;
+            while (current != child) {
+                scrollOffsetToChild += current.geometry.scrollExtent;
+                current = this.childAfter(current);
+            }
+
+            return scrollOffsetToChild + scrollOffsetWithinChild;
+        }
+
+        public override double maxScrollObstructionExtentBefore(RenderSliver child) {
+            double pinnedExtent = 0.0;
+            RenderSliver current = this.firstChild;
+            while (current != child) {
+                pinnedExtent += current.geometry.maxScrollObstructionExtent;
+                current = this.childAfter(current);
+            }
+
+            return pinnedExtent;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+            Offset offset = this.paintOffsetOf((RenderSliver) child);
+            transform = Matrix4x4.Translate(offset.toVector()) * transform;
+        }
+
+        public override IEnumerable<RenderSliver> childrenInPaintOrder {
+            get {
+                RenderSliver child = this.firstChild;
+                while (child != null) {
+                    yield return child;
+                    child = this.childAfter(child);
+                }
+            }
         }
     }
 }

Assets/UIWidgets/rendering/viewport_offset.cs

-using UIWidgets.foundation;
+using System;
+using UIWidgets.foundation;
 
 namespace UIWidgets.rendering {
     public enum ScrollDirection {
     }
-    
+
+    public static class ScrollDirectionUtils {
+        public static ScrollDirection flipScrollDirection(ScrollDirection direction) {
+            switch (direction) {
+                case ScrollDirection.idle:
+                    return ScrollDirection.idle;
+                case ScrollDirection.forward:
+                    return ScrollDirection.reverse;
+                case ScrollDirection.reverse:
+                    return ScrollDirection.forward;
+            }
+
+            throw new Exception("unknown direction");
+        }
+    }
+
-            return null;
+            return new _FixedViewportOffset(value);
-            return null;
+            return _FixedViewportOffset.zero();
         }
 
         public abstract double pixels { get; }
         public abstract void correctBy(double correction);
         public abstract void jumpTo(double pixels);
+
+        public abstract ScrollDirection userScrollDirection { get; }
+    }
+
+    public class _FixedViewportOffset : ViewportOffset {
+        public _FixedViewportOffset(double _pixels) {
+            this._pixels = _pixels;
+        }
+
+        public new static _FixedViewportOffset zero() {
+            return new _FixedViewportOffset(0.0);
+        }
+
+        public double _pixels;
+
+        public override double pixels {
+            get { return this._pixels; }
+        }
+
+        public override bool applyViewportDimension(double viewportDimension) {
+            return true;
+        }
+
+        public override bool applyContentDimensions(double minScrollExtent, double maxScrollExtent) {
+            return true;
+        }
+
+        public override void correctBy(double correction) {
+            this._pixels += correction;
+        }
+
+        public override void jumpTo(double pixels) {
+        }
+
+        public override ScrollDirection userScrollDirection {
+            get { return ScrollDirection.idle; }
+        }
     }
 }

Assets/UIWidgets/ui/geometry.cs

 using System;
 
 namespace UIWidgets.ui {
+    public static class MathUtils {
+        public static double clamp(this double value, double min, double max) {
+            if (value < min) {
+                value = min;
+            } else if (value > max) {
+                value = max;
+            }
+
+            return value;
+        }
+
+        public static int clamp(this int value, int min, int max) {
+            if (value < min) {
+                value = min;
+            } else if (value > max) {
+                value = max;
+            }
+
+            return value;
+        }
+    }
+
     public abstract class OffsetBase : IEquatable<OffsetBase> {
         protected OffsetBase(double _dx, double _dy) {
             this._dx = _dx;
 
         public static Offset operator +(Offset a, Offset b) {
             return new Offset(a.dx + b.dx, a.dy + b.dy);
+        }
+
+        public static Offset operator *(Offset a, double operand) {
+            return new Offset(a.dx * operand, a.dy * operand);
+        }
+
+        public static Offset operator /(Offset a, double operand) {
+            return new Offset(a.dx / operand, a.dy / operand);
         }
 
         public static Rect operator &(Offset a, Size other) {
         public static Offset operator -(Size a, Size b) {
             return new Offset(a.width - b.width, a.height - b.width);
         }
-        
+
         public static Size operator *(Size a, double operand) {
             return new Size(a.width * operand, a.height * operand);
         }
                 this.bottom + offset.dy);
         }
 
+        public Rect translate(double translateX, double translateY) {
+            return Rect.fromLTRB(this.left + translateX, this.top + translateY, this.right + translateX,
+                this.bottom + translateY);
+        }
+
         public Rect inflate(double delta) {
             return Rect.fromLTRB(this.left - delta, this.top - delta, this.right + delta, this.bottom + delta);
         }
         public bool contains(Offset offset) {
             return offset.dx >= this.left && offset.dx < this.right && offset.dy >= this.top && offset.dy < this.bottom;
         }
-        
+
         public bool contains(Rect rect) {
             return this.contains(rect.topLeft) && this.contains(rect.bottomRight);
         }

Assets/UIWidgets/rendering/sliver_fixed_extent_list.cs

+using System;
+using UIWidgets.ui;
+
+namespace UIWidgets.rendering {
+    public abstract class RenderSliverFixedExtentBoxAdaptor : RenderSliverMultiBoxAdaptor {
+        RenderSliverFixedExtentBoxAdaptor(
+            RenderSliverBoxChildManager childManager = null
+        ) : base(childManager: childManager) {
+        }
+
+        public abstract double itemExtent { get; }
+
+        public double indexToLayoutOffset(double itemExtent, int index) {
+            return itemExtent * index;
+        }
+
+        public int getMinChildIndexForScrollOffset(double scrollOffset, double itemExtent) {
+            return itemExtent > 0.0 ? Math.Max(0, (int) (scrollOffset / itemExtent)) : 0;
+        }
+
+        public int getMaxChildIndexForScrollOffset(double scrollOffset, double itemExtent) {
+            return itemExtent > 0.0 ? Math.Max(0, (int) Math.Ceiling(scrollOffset / itemExtent) - 1) : 0;
+        }
+
+        public double estimateMaxScrollOffset(SliverConstraints constraints,
+            int firstIndex = 0,
+            int lastIndex = 0,
+            double leadingScrollOffset = 0.0,
+            double trailingScrollOffset = 0.0
+        ) {
+            return this.childManager.estimateMaxScrollOffset(
+                constraints,
+                firstIndex: firstIndex,
+                lastIndex: lastIndex,
+                leadingScrollOffset: leadingScrollOffset,
+                trailingScrollOffset: trailingScrollOffset
+            );
+        }
+
+        public double computeMaxScrollOffset(SliverConstraints constraints, double itemExtent) {
+            return this.childManager.childCount * itemExtent;
+        }
+
+
+        public override void performLayout() {
+            this.childManager.didStartLayout();
+            this.childManager.setDidUnderflow(false);
+
+            double itemExtent = this.itemExtent;
+
+            double scrollOffset = this.constraints.scrollOffset + this.constraints.cacheOrigin;
+            double remainingExtent = this.constraints.remainingCacheExtent;
+            double targetEndScrollOffset = scrollOffset + remainingExtent;
+
+            BoxConstraints childConstraints = this.constraints.asBoxConstraints(
+                minExtent: itemExtent,
+                maxExtent: itemExtent
+            );
+
+            int firstIndex = this.getMinChildIndexForScrollOffset(scrollOffset, itemExtent);
+            int? targetLastIndex = !double.IsInfinity(targetEndScrollOffset)
+                ? this.getMaxChildIndexForScrollOffset(targetEndScrollOffset, itemExtent)
+                : (int?) null;
+
+            if (this.firstChild != null) {
+                int oldFirstIndex = this.indexOf(this.firstChild);
+                int oldLastIndex = this.indexOf(this.lastChild);
+                int leadingGarbage = (firstIndex - oldFirstIndex).clamp(0, this.childCount);
+                int trailingGarbage =
+                    targetLastIndex == null ? 0 : (oldLastIndex - targetLastIndex.Value).clamp(0, this.childCount);
+                this.collectGarbage(leadingGarbage, trailingGarbage);
+            } else {
+                this.collectGarbage(0, 0);
+            }
+
+            if (this.firstChild == null) {
+                if (!this.addInitialChild(index: firstIndex,
+                    layoutOffset: this.indexToLayoutOffset(itemExtent, firstIndex))) {
+                    double max = this.computeMaxScrollOffset(this.constraints, itemExtent);
+                    this.geometry = new SliverGeometry(
+                        scrollExtent: max,
+                        maxPaintExtent: max
+                    );
+                    this.childManager.didFinishLayout();
+                    return;
+                }
+            }
+
+            RenderBox trailingChildWithLayout = null;
+
+            for (int index = this.indexOf(this.firstChild) - 1; index >= firstIndex; --index) {
+                RenderBox child = this.insertAndLayoutLeadingChild(childConstraints);
+                if (child == null) {
+                    this.geometry = new SliverGeometry(scrollOffsetCorrection: index * itemExtent);
+                    return;
+                }
+
+                var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+                childParentData.layoutOffset = this.indexToLayoutOffset(itemExtent, index);
+                trailingChildWithLayout = trailingChildWithLayout ?? child;
+            }
+
+            if (trailingChildWithLayout == null) {
+                this.firstChild.layout(childConstraints);
+                var childParentData = (SliverMultiBoxAdaptorParentData) this.firstChild.parentData;
+                childParentData.layoutOffset = this.indexToLayoutOffset(itemExtent, firstIndex);
+                trailingChildWithLayout = this.firstChild;
+            }
+
+            while (targetLastIndex == null || this.indexOf(trailingChildWithLayout) < targetLastIndex) {
+                RenderBox child = this.childAfter(trailingChildWithLayout);
+                if (child == null) {
+                    child = this.insertAndLayoutChild(childConstraints, after: trailingChildWithLayout);
+                    if (child == null) {
+                        break;
+                    }
+                } else {
+                    child.layout(childConstraints);
+                }
+
+                trailingChildWithLayout = child;
+                var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+                childParentData.layoutOffset = this.indexToLayoutOffset(itemExtent, childParentData.index);
+            }
+
+            int lastIndex = this.indexOf(this.lastChild);
+            double leadingScrollOffset = this.indexToLayoutOffset(itemExtent, firstIndex);
+            double trailingScrollOffset = this.indexToLayoutOffset(itemExtent, lastIndex + 1);
+
+            double estimatedMaxScrollOffset = this.estimateMaxScrollOffset(
+                this.constraints,
+                firstIndex: firstIndex,
+                lastIndex: lastIndex,
+                leadingScrollOffset: leadingScrollOffset,
+                trailingScrollOffset: trailingScrollOffset
+            );
+
+            double paintExtent = this.calculatePaintOffset(
+                this.constraints,
+                from: leadingScrollOffset,
+                to: trailingScrollOffset
+            );
+
+            double cacheExtent = this.calculateCacheOffset(
+                this.constraints,
+                from: leadingScrollOffset,
+                to: trailingScrollOffset
+            );
+
+            double targetEndScrollOffsetForPaint =
+                this.constraints.scrollOffset + this.constraints.remainingPaintExtent;
+            int? targetLastIndexForPaint = !double.IsInfinity(targetEndScrollOffsetForPaint)
+                ? this.getMaxChildIndexForScrollOffset(targetEndScrollOffsetForPaint, itemExtent)
+                : (int?) null;
+            this.geometry = new SliverGeometry(
+                scrollExtent: estimatedMaxScrollOffset,
+                paintExtent: paintExtent,
+                cacheExtent: cacheExtent,
+                maxPaintExtent: estimatedMaxScrollOffset,
+                hasVisualOverflow: (targetLastIndexForPaint != null && lastIndex >= targetLastIndexForPaint)
+                                   || this.constraints.scrollOffset > 0.0
+            );
+            if (estimatedMaxScrollOffset == trailingScrollOffset) {
+                this.childManager.setDidUnderflow(true);
+            }
+
+            this.childManager.didFinishLayout();
+        }
+    }
+}

Assets/UIWidgets/rendering/sliver_fixed_extent_list.cs.meta

+fileFormatVersion: 2
+guid: e602742e1e9c408989efd79055a9e552
+timeCreated: 1535524936

Assets/UIWidgets/rendering/sliver_list.cs

+using System;
+
+namespace UIWidgets.rendering {
+    public class RenderSliverList : RenderSliverMultiBoxAdaptor {
+        RenderSliverList(
+            RenderSliverBoxChildManager childManager = null
+        ) : base(childManager: childManager) {
+        }
+
+        public override void performLayout() {
+            this.childManager.didStartLayout();
+            this.childManager.setDidUnderflow(false);
+
+            double scrollOffset = this.constraints.scrollOffset + this.constraints.cacheOrigin;
+            double remainingExtent = this.constraints.remainingCacheExtent;
+            double targetEndScrollOffset = scrollOffset + remainingExtent;
+            BoxConstraints childConstraints = this.constraints.asBoxConstraints();
+            int leadingGarbage = 0;
+            int trailingGarbage = 0;
+            bool reachedEnd = false;
+
+            if (this.firstChild == null) {
+                if (!this.addInitialChild()) {
+                    this.geometry = SliverGeometry.zero;
+                    this.childManager.didFinishLayout();
+                    return;
+                }
+            }
+
+            RenderBox leadingChildWithLayout = null, trailingChildWithLayout = null;
+
+            RenderBox earliestUsefulChild = this.firstChild;
+            for (double earliestScrollOffset = this.childScrollOffset(earliestUsefulChild);
+                earliestScrollOffset > scrollOffset;
+                earliestScrollOffset = this.childScrollOffset(earliestUsefulChild)) {
+                earliestUsefulChild = this.insertAndLayoutLeadingChild(childConstraints, parentUsesSize: true);
+
+                if (earliestUsefulChild == null) {
+                    var childParentData = (SliverMultiBoxAdaptorParentData) this.firstChild.parentData;
+                    childParentData.layoutOffset = 0.0;
+
+                    if (scrollOffset == 0.0) {
+                        earliestUsefulChild = this.firstChild;
+                        leadingChildWithLayout = earliestUsefulChild;
+                        trailingChildWithLayout = trailingChildWithLayout ?? earliestUsefulChild;
+                        break;
+                    } else {
+                        this.geometry = new SliverGeometry(
+                            scrollOffsetCorrection: -scrollOffset
+                        );
+                        return;
+                    }
+                } else {
+                    double firstChildScrollOffset = earliestScrollOffset - this.paintExtentOf(this.firstChild);
+                    if (firstChildScrollOffset < 0.0) {
+                        double correction = 0.0;
+                        while (earliestUsefulChild != null) {
+                            correction += this.paintExtentOf(firstChild);
+                            earliestUsefulChild =
+                                this.insertAndLayoutLeadingChild(childConstraints, parentUsesSize: true);
+                        }
+
+                        this.geometry = new SliverGeometry(
+                            scrollOffsetCorrection: correction - earliestScrollOffset
+                        );
+                        var childParentData = (SliverMultiBoxAdaptorParentData) this.firstChild.parentData;
+                        childParentData.layoutOffset = 0.0;
+                        return;
+                    } else {
+                        var childParentData = (SliverMultiBoxAdaptorParentData) earliestUsefulChild.parentData;
+                        childParentData.layoutOffset = firstChildScrollOffset;
+                        leadingChildWithLayout = earliestUsefulChild;
+                        trailingChildWithLayout = trailingChildWithLayout ?? earliestUsefulChild;
+                    }
+                }
+            }
+
+            if (leadingChildWithLayout == null) {
+                earliestUsefulChild.layout(childConstraints, parentUsesSize: true);
+                leadingChildWithLayout = earliestUsefulChild;
+                trailingChildWithLayout = earliestUsefulChild;
+            }
+
+            bool inLayoutRange = true;
+            RenderBox child = earliestUsefulChild;
+            int index = this.indexOf(child);
+            double endScrollOffset = this.childScrollOffset(child) + this.paintExtentOf(child);
+
+            Func<bool> advance = () => {
+                if (child == trailingChildWithLayout) {
+                    inLayoutRange = false;
+                }
+
+                child = this.childAfter(child);
+                if (child == null) {
+                    inLayoutRange = false;
+                }
+
+                index += 1;
+                if (!inLayoutRange) {
+                    if (child == null || this.indexOf(child) != index) {
+                        child = insertAndLayoutChild(childConstraints,
+                            after: trailingChildWithLayout,
+                            parentUsesSize: true
+                        );
+                        if (child == null) {
+                            return false;
+                        }
+                    } else {
+                        child.layout(childConstraints, parentUsesSize: true);
+                    }
+
+                    trailingChildWithLayout = child;
+                }
+
+                var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+                childParentData.layoutOffset = endScrollOffset;
+                endScrollOffset = this.childScrollOffset(child) + this.paintExtentOf(child);
+                return true;
+            };
+
+            while (endScrollOffset < scrollOffset) {
+                leadingGarbage += 1;
+                if (!advance()) {
+                    this.collectGarbage(leadingGarbage - 1, 0);
+                    double extent = this.childScrollOffset(this.lastChild) + this.paintExtentOf(this.lastChild);
+                    this.geometry = new SliverGeometry(
+                        scrollExtent: extent,
+                        paintExtent: 0.0,
+                        maxPaintExtent: extent
+                    );
+                    return;
+                }
+            }
+
+            while (endScrollOffset < targetEndScrollOffset) {
+                if (!advance()) {
+                    reachedEnd = true;
+                    break;
+                }
+            }
+
+            if (child != null) {
+                child = this.childAfter(child);
+                while (child != null) {
+                    trailingGarbage += 1;
+                    child = this.childAfter(child);
+                }
+            }
+
+            this.collectGarbage(leadingGarbage, trailingGarbage);
+
+            double estimatedMaxScrollOffset;
+            if (reachedEnd) {
+                estimatedMaxScrollOffset = endScrollOffset;
+            } else {
+                estimatedMaxScrollOffset = this.childManager.estimateMaxScrollOffset(
+                    this.constraints,
+                    firstIndex: this.indexOf(this.firstChild),
+                    lastIndex: this.indexOf(this.lastChild),
+                    leadingScrollOffset: this.childScrollOffset(this.firstChild),
+                    trailingScrollOffset: endScrollOffset
+                );
+            }
+
+            double paintExtent = this.calculatePaintOffset(
+                this.constraints,
+                from: this.childScrollOffset(this.firstChild),
+                to: endScrollOffset
+            );
+            double cacheExtent = this.calculateCacheOffset(
+                this.constraints,
+                from: this.childScrollOffset(this.firstChild),
+                to: endScrollOffset
+            );
+            double targetEndScrollOffsetForPaint =
+                this.constraints.scrollOffset + this.constraints.remainingPaintExtent;
+            this.geometry = new SliverGeometry(
+                scrollExtent: estimatedMaxScrollOffset,
+                paintExtent: paintExtent,
+                cacheExtent: cacheExtent,
+                maxPaintExtent: estimatedMaxScrollOffset,
+                hasVisualOverflow: endScrollOffset > targetEndScrollOffsetForPaint ||
+                                   this.constraints.scrollOffset > 0.0
+            );
+
+            if (estimatedMaxScrollOffset == endScrollOffset) {
+                this.childManager.setDidUnderflow(true);
+            }
+
+            this.childManager.didFinishLayout();
+        }
+    }
+}

Assets/UIWidgets/rendering/sliver_list.cs.meta

+fileFormatVersion: 2
+guid: 1db4d92862744fcdb527f4020106fdf8
+timeCreated: 1535522746

Assets/UIWidgets/rendering/sliver_multi_box_adaptor.cs

+using System.Collections.Generic;
+using System.Linq;
+using UIWidgets.foundation;
+using UIWidgets.painting;
+using UIWidgets.ui;
+using UnityEngine;
+
+namespace UIWidgets.rendering {
+    public interface RenderSliverBoxChildManager {
+        void createChild(int index, RenderBox after = null);
+
+        void removeChild(RenderBox child);
+
+        double estimateMaxScrollOffset(
+            SliverConstraints constraints,
+            int firstIndex = 0,
+            int lastIndex = 0,
+            double leadingScrollOffset = 0,
+            double trailingScrollOffset = 0);
+
+        int childCount { get; }
+
+        void didAdoptChild(RenderBox child);
+
+        void setDidUnderflow(bool value);
+
+        void didStartLayout();
+
+        void didFinishLayout();
+    }
+
+    public class SliverMultiBoxAdaptorParentData : ContainerParentDataMixinSliverLogicalParentData<RenderBox> {
+        public int index;
+
+        public bool keepAlive = false;
+
+        public bool _keptAlive = false;
+    }
+
+    public abstract class RenderSliverMultiBoxAdaptor
+        : ContainerRenderObjectMixinRenderSliver<RenderBox, SliverMultiBoxAdaptorParentData> {
+        public RenderSliverMultiBoxAdaptor(
+            RenderSliverBoxChildManager childManager = null
+        ) {
+            this._childManager = childManager;
+        }
+
+        public override void setupParentData(RenderObject child) {
+            if (!(child.parentData is SliverMultiBoxAdaptorParentData)) {
+                child.parentData = new SliverMultiBoxAdaptorParentData();
+            }
+        }
+
+        public RenderSliverBoxChildManager childManager {
+            get { return this._childManager; }
+        }
+
+        public RenderSliverBoxChildManager _childManager;
+
+        public readonly Dictionary<int, RenderBox> _keepAliveBucket = new Dictionary<int, RenderBox>();
+
+        public override void adoptChild(AbstractNode childNode) {
+            base.adoptChild(childNode);
+            var child = (RenderBox) childNode;
+            var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+            if (!childParentData._keptAlive) {
+                this.childManager.didAdoptChild(child);
+            }
+        }
+
+        public override void insert(RenderBox child, RenderBox after = null) {
+            base.insert(child, after: after);
+        }
+
+        public override void remove(RenderBox child) {
+            var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+            if (!childParentData._keptAlive) {
+                base.remove(child);
+                return;
+            }
+
+            this._keepAliveBucket.Remove(childParentData.index);
+            this.dropChild(child);
+        }
+
+        public override void removeAll() {
+            base.removeAll();
+
+            foreach (var child in this._keepAliveBucket.Values) {
+                this.dropChild(child);
+            }
+
+            this._keepAliveBucket.Clear();
+        }
+
+        void _createOrObtainChild(int index, RenderBox after = null) {
+            this.invokeLayoutCallback<SliverConstraints>((SliverConstraints constraints) => {
+                if (this._keepAliveBucket.ContainsKey(index)) {
+                    RenderBox child = this._keepAliveBucket[index];
+                    this._keepAliveBucket.Remove(index);
+                    var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+                    this.dropChild(child);
+                    child.parentData = childParentData;
+                    this.insert(child, after: after);
+                    childParentData._keptAlive = false;
+                } else {
+                    this._childManager.createChild(index, after: after);
+                }
+            });
+        }
+
+        public void _destroyOrCacheChild(RenderBox child) {
+            var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+            if (childParentData.keepAlive) {
+                this.remove(child);
+                this._keepAliveBucket[childParentData.index] = child;
+                child.parentData = childParentData;
+                base.adoptChild(child);
+                childParentData._keptAlive = true;
+            } else {
+                this._childManager.removeChild(child);
+            }
+        }
+
+        public override void attach(object owner) {
+            base.attach(owner);
+            foreach (RenderBox child in this._keepAliveBucket.Values) {
+                child.attach(owner);
+            }
+        }
+
+        public override void detach() {
+            base.detach();
+            foreach (RenderBox child in this._keepAliveBucket.Values) {
+                child.detach();
+            }
+        }
+
+        public override void redepthChildren() {
+            base.redepthChildren();
+            foreach (var child in this._keepAliveBucket.Values) {
+                this.redepthChild(child);
+            }
+        }
+
+        public override void visitChildren(RenderObjectVisitor visitor) {
+            base.visitChildren(visitor);
+
+            foreach (var child in this._keepAliveBucket.Values) {
+                visitor(child);
+            }
+        }
+
+        public bool addInitialChild(int index = 0, double layoutOffset = 0.0) {
+            this._createOrObtainChild(index, after: null);
+            if (this.firstChild != null) {
+                var firstChildParentData = (SliverMultiBoxAdaptorParentData) this.firstChild.parentData;
+                firstChildParentData.layoutOffset = layoutOffset;
+                return true;
+            }
+
+            this.childManager.setDidUnderflow(true);
+            return false;
+        }
+
+        public RenderBox insertAndLayoutLeadingChild(BoxConstraints childConstraints, bool parentUsesSize = false) {
+            int index = this.indexOf(this.firstChild) - 1;
+            this._createOrObtainChild(index, after: null);
+            if (this.indexOf(this.firstChild) == index) {
+                this.firstChild.layout(childConstraints, parentUsesSize: parentUsesSize);
+                return this.firstChild;
+            }
+
+            this.childManager.setDidUnderflow(true);
+            return null;
+        }
+
+        public RenderBox insertAndLayoutChild(
+            BoxConstraints childConstraints,
+            RenderBox after = null,
+            bool parentUsesSize = false
+        ) {
+            int index = this.indexOf(after) + 1;
+            this._createOrObtainChild(index, after: after);
+            RenderBox child = this.childAfter(after);
+            if (child != null && this.indexOf(child) == index) {
+                child.layout(childConstraints, parentUsesSize: parentUsesSize);
+                return child;
+            }
+
+            this.childManager.setDidUnderflow(true);
+            return null;
+        }
+
+        public void collectGarbage(int leadingGarbage, int trailingGarbage) {
+            this.invokeLayoutCallback<SliverConstraints>((SliverConstraints constraints) => {
+                while (leadingGarbage > 0) {
+                    this._destroyOrCacheChild(this.firstChild);
+                    leadingGarbage -= 1;
+                }
+
+                while (trailingGarbage > 0) {
+                    this._destroyOrCacheChild(this.lastChild);
+                    trailingGarbage -= 1;
+                }
+
+                this._keepAliveBucket.Values.Where((RenderBox child) => {
+                    var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+                    return !childParentData.keepAlive;
+                }).ToList().ForEach(this._childManager.removeChild);
+            });
+        }
+
+        public int indexOf(RenderBox child) {
+            var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+            return childParentData.index;
+        }
+
+        public double paintExtentOf(RenderBox child) {
+            switch (this.constraints.axis) {
+                case Axis.horizontal:
+                    return child.size.width;
+                case Axis.vertical:
+                    return child.size.height;
+            }
+
+            return 0.0;
+        }
+
+        public override double childMainAxisPosition(RenderObject child) {
+            return this.childScrollOffset(child) - this.constraints.scrollOffset;
+        }
+
+        public override double childScrollOffset(RenderObject child) {
+            var childParentData = (SliverMultiBoxAdaptorParentData) child.parentData;
+            return childParentData.layoutOffset;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+            this.applyPaintTransformForBoxChild((RenderBox) child, ref transform);
+        }
+
+        public override void paint(PaintingContext context, Offset offset) {
+            if (this.firstChild == null) {
+                return;
+            }
+
+            Offset mainAxisUnit = null, crossAxisUnit = null, originOffset = null;
+            bool addExtent = false;
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(this.constraints.axisDirection,
+                this.constraints.growthDirection)) {
+                case AxisDirection.up:
+                    mainAxisUnit = new Offset(0.0, -1.0);
+                    crossAxisUnit = new Offset(1.0, 0.0);
+                    originOffset = offset + new Offset(0.0, this.geometry.paintExtent);
+                    addExtent = true;
+                    break;
+                case AxisDirection.right:
+                    mainAxisUnit = new Offset(1.0, 0.0);
+                    crossAxisUnit = new Offset(0.0, 1.0);
+                    originOffset = offset;
+                    addExtent = false;
+                    break;
+                case AxisDirection.down:
+                    mainAxisUnit = new Offset(0.0, 1.0);
+                    crossAxisUnit = new Offset(1.0, 0.0);
+                    originOffset = offset;
+                    addExtent = false;
+                    break;
+                case AxisDirection.left:
+                    mainAxisUnit = new Offset(-1.0, 0.0);
+                    crossAxisUnit = new Offset(0.0, 1.0);
+                    originOffset = offset + new Offset(this.geometry.paintExtent, 0.0);
+                    addExtent = true;
+                    break;
+            }
+
+            RenderBox child = this.firstChild;
+            while (child != null) {
+                double mainAxisDelta = this.childMainAxisPosition(child);
+                double crossAxisDelta = this.childCrossAxisPosition(child);
+                Offset childOffset = new Offset(
+                    originOffset.dx + mainAxisUnit.dx * mainAxisDelta + crossAxisUnit.dx * crossAxisDelta,
+                    originOffset.dy + mainAxisUnit.dy * mainAxisDelta + crossAxisUnit.dy * crossAxisDelta
+                );
+                if (addExtent) {
+                    childOffset += mainAxisUnit * this.paintExtentOf(child);
+                }
+
+                if (mainAxisDelta < this.constraints.remainingPaintExtent &&
+                    mainAxisDelta + this.paintExtentOf(child) > 0) {
+                    context.paintChild(child, childOffset);
+                }
+
+                child = this.childAfter(child);
+            }
+        }
+    }
+}

Assets/UIWidgets/rendering/sliver_multi_box_adaptor.cs.meta

+fileFormatVersion: 2
+guid: 00853d7738fe40eeb3e7b44db23248be
+timeCreated: 1535502825

Assets/UIWidgets/rendering/sliver_padding.cs

+using System;
+using UIWidgets.painting;
+using UIWidgets.ui;
+using UnityEngine;
+
+namespace UIWidgets.rendering {
+    public class RenderSliverPadding : RenderObjectWithChildMixinRenderSliver<RenderSliver> {
+        RenderSliverPadding(
+            EdgeInsets padding,
+            RenderSliver child
+        ) {
+            this._padding = padding;
+            this.child = child;
+        }
+
+        public EdgeInsets padding {
+            get { return this._padding; }
+            set {
+                if (this._padding == value) {
+                    return;
+                }
+
+                this._padding = value;
+                this.markNeedsLayout();
+            }
+        }
+
+        public EdgeInsets _padding;
+
+        public double beforePadding {
+            get {
+                switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(
+                    this.constraints.axisDirection, this.constraints.growthDirection)) {
+                    case AxisDirection.up:
+                        return this._padding.bottom;
+                    case AxisDirection.right:
+                        return this._padding.left;
+                    case AxisDirection.down:
+                        return this._padding.top;
+                    case AxisDirection.left:
+                        return this._padding.right;
+                }
+
+                return 0.0;
+            }
+        }
+
+        public double afterPadding {
+            get {
+                switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(
+                    this.constraints.axisDirection, this.constraints.growthDirection)) {
+                    case AxisDirection.up:
+                        return this._padding.top;
+                    case AxisDirection.right:
+                        return this._padding.right;
+                    case AxisDirection.down:
+                        return this._padding.bottom;
+                    case AxisDirection.left:
+                        return this._padding.left;
+                }
+
+                return 0.0;
+            }
+        }
+
+        public double mainAxisPadding {
+            get { return this._padding.along(this.constraints.axis); }
+        }
+
+        public double crossAxisPadding {
+            get {
+                switch (this.constraints.axis) {
+                    case Axis.horizontal:
+                        return this._padding.vertical;
+                    case Axis.vertical:
+                        return this._padding.horizontal;
+                }
+
+                return 0.0;
+            }
+        }
+
+        public override void setupParentData(RenderObject child) {
+            if (!(child.parentData is SliverPhysicalParentData)) {
+                child.parentData = new SliverPhysicalParentData();
+            }
+        }
+
+        public override void performLayout() {
+            double beforePadding = this.beforePadding;
+            double afterPadding = this.afterPadding;
+            double mainAxisPadding = this.mainAxisPadding;
+            double crossAxisPadding = this.crossAxisPadding;
+            if (this.child == null) {
+                this.geometry = new SliverGeometry(
+                    scrollExtent: mainAxisPadding,
+                    paintExtent: Math.Min(mainAxisPadding, this.constraints.remainingPaintExtent),
+                    maxPaintExtent: mainAxisPadding
+                );
+                return;
+            }
+
+            this.child.layout(
+                this.constraints.copyWith(
+                    scrollOffset: Math.Max(0.0, this.constraints.scrollOffset - beforePadding),
+                    cacheOrigin: Math.Min(0.0, this.constraints.cacheOrigin + beforePadding),
+                    overlap: 0.0,
+                    remainingPaintExtent: this.constraints.remainingPaintExtent -
+                                          this.calculatePaintOffset(this.constraints, from: 0.0, to: beforePadding),
+                    remainingCacheExtent: this.constraints.remainingCacheExtent -
+                                          this.calculateCacheOffset(this.constraints, from: 0.0, to: beforePadding),
+                    crossAxisExtent: Math.Max(0.0, this.constraints.crossAxisExtent - crossAxisPadding)
+                ),
+                parentUsesSize: true
+            );
+
+            SliverGeometry childLayoutGeometry = this.child.geometry;
+            if (childLayoutGeometry.scrollOffsetCorrection != 0.0) {
+                this.geometry = new SliverGeometry(
+                    scrollOffsetCorrection: childLayoutGeometry.scrollOffsetCorrection
+                );
+                return;
+            }
+
+            double beforePaddingPaintExtent = this.calculatePaintOffset(
+                this.constraints,
+                from: 0.0,
+                to: beforePadding
+            );
+
+            double afterPaddingPaintExtent = this.calculatePaintOffset(
+                this.constraints,
+                from: beforePadding + childLayoutGeometry.scrollExtent,
+                to: mainAxisPadding + childLayoutGeometry.scrollExtent
+            );
+
+            double mainAxisPaddingPaintExtent = beforePaddingPaintExtent + afterPaddingPaintExtent;
+            double beforePaddingCacheExtent = this.calculateCacheOffset(
+                this.constraints,
+                from: 0.0,
+                to: beforePadding
+            );
+            double afterPaddingCacheExtent = this.calculateCacheOffset(
+                this.constraints,
+                from: beforePadding + childLayoutGeometry.scrollExtent,
+                to: mainAxisPadding + childLayoutGeometry.scrollExtent
+            );
+
+            double mainAxisPaddingCacheExtent = afterPaddingCacheExtent + beforePaddingCacheExtent;
+            double paintExtent = Math.Min(
+                beforePaddingPaintExtent + Math.Max(childLayoutGeometry.paintExtent,
+                    childLayoutGeometry.layoutExtent + afterPaddingPaintExtent),
+                this.constraints.remainingPaintExtent
+            );
+
+            this.geometry = new SliverGeometry(
+                scrollExtent: mainAxisPadding + childLayoutGeometry.scrollExtent,
+                paintExtent: paintExtent,
+                layoutExtent: Math.Min(mainAxisPaddingPaintExtent + childLayoutGeometry.layoutExtent, paintExtent),
+                cacheExtent: Math.Min(mainAxisPaddingCacheExtent + childLayoutGeometry.cacheExtent,
+                    this.constraints.remainingCacheExtent),
+                maxPaintExtent: mainAxisPadding + childLayoutGeometry.maxPaintExtent,
+                hitTestExtent: Math.Max(
+                    mainAxisPaddingPaintExtent + childLayoutGeometry.paintExtent,
+                    beforePaddingPaintExtent + childLayoutGeometry.hitTestExtent
+                ),
+                hasVisualOverflow: childLayoutGeometry.hasVisualOverflow
+            );
+
+            var childParentData = (SliverPhysicalParentData) this.child.parentData;
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(this.constraints.axisDirection,
+                this.constraints.growthDirection)) {
+                case AxisDirection.up:
+                    childParentData.paintOffset = new Offset(this._padding.left,
+                        this.calculatePaintOffset(this.constraints,
+                            from: this._padding.bottom + childLayoutGeometry.scrollExtent,
+                            to: this._padding.bottom + childLayoutGeometry.scrollExtent + this._padding.top));
+                    break;
+                case AxisDirection.right:
+                    childParentData.paintOffset =
+                        new Offset(this.calculatePaintOffset(this.constraints, from: 0.0, to: this._padding.left),
+                            this._padding.top);
+                    break;
+                case AxisDirection.down:
+                    childParentData.paintOffset = new Offset(this._padding.left,
+                        this.calculatePaintOffset(this.constraints, from: 0.0, to: this._padding.top));
+                    break;
+                case AxisDirection.left:
+                    childParentData.paintOffset = new Offset(
+                        this.calculatePaintOffset(this.constraints,
+                            from: this._padding.right + childLayoutGeometry.scrollExtent,
+                            to: this._padding.right + childLayoutGeometry.scrollExtent + this._padding.left),
+                        this._padding.top);
+                    break;
+            }
+        }
+
+        public override double childMainAxisPosition(RenderObject child) {
+            return this.calculatePaintOffset(this.constraints, from: 0.0, to: this.beforePadding);
+        }
+
+        public override double childCrossAxisPosition(RenderObject child) {
+            switch (GrowthDirectionUtils.applyGrowthDirectionToAxisDirection(
+                this.constraints.axisDirection, this.constraints.growthDirection)) {
+                case AxisDirection.up:
+                case AxisDirection.down:
+                    return this._padding.left;
+                case AxisDirection.left:
+                case AxisDirection.right:
+                    return this._padding.top;
+            }
+
+            return 0.0;
+        }
+
+        public override double childScrollOffset(RenderObject child) {
+            return this.beforePadding;
+        }
+
+        public override void applyPaintTransform(RenderObject child, ref Matrix4x4 transform) {
+            var childParentData = (SliverPhysicalParentData) child.parentData;
+            childParentData.applyPaintTransform(ref transform);
+        }
+
+        public override void paint(PaintingContext context, Offset offset) {
+            if (this.child != null && this.child.geometry.visible) {
+                var childParentData = (SliverPhysicalParentData) this.child.parentData;
+                context.paintChild(this.child, offset + childParentData.paintOffset);
+            }
+        }
+    }
+}

Assets/UIWidgets/rendering/sliver_padding.cs.meta

+fileFormatVersion: 2
+guid: 470336df9a5d4af3a4ccfa5fa759d854
+timeCreated: 1535523877

Assets/UIWidgets/gestures/arena.cs

+namespace UIWidgets.gestures {
+}