com.unity.uiwidgets/com.unity.uiwidgets/Runtime/widgets/visibility.cs

using Unity.UIWidgets.foundation;

namespace Unity.UIWidgets.widgets {
    public class Visibility : StatelessWidget {
        public Visibility(
            Key key = null,
            Widget child = null,
            Widget replacement = null,
            bool visible = true,
            bool maintainState = false,
            bool maintainAnimation = false,
            bool maintainSize = false,
            bool maintainSemantics = false,
            bool maintainInteractivity = false
        ) : base(key: key) {
            D.assert(child != null);
            D.assert(maintainState == true || maintainAnimation == false,
                () => "Cannot maintain animations if the state is not also maintained.");
            D.assert(maintainAnimation == true || maintainSize == false,
                () => "Cannot maintain size if animations are not maintained.");
            D.assert(
                maintainSize == true || maintainSemantics == false,
                ()=>"Cannot maintain semantics if size is not maintained."
            );
            D.assert(maintainSize == true || maintainInteractivity == false,
                () => "Cannot maintain interactivity if size is not maintained.");
            this.replacement = replacement ?? SizedBox.shrink();
            this.child = child;
            this.visible = visible;
            this.maintainState = maintainState;
            this.maintainAnimation = maintainAnimation;
            this.maintainSize = maintainSize;
            this.maintainSemantics = maintainSemantics;
            this.maintainInteractivity = maintainInteractivity;
        }

        public readonly Widget child;

        public readonly Widget replacement;

        public readonly bool visible;

        public readonly bool maintainState;

        public readonly bool maintainAnimation;

        public readonly bool maintainSize;

        public readonly bool maintainSemantics;

        public readonly bool maintainInteractivity;

        public override Widget build(BuildContext context) {
            if (maintainSize) {
                Widget result = child;
                if (!maintainInteractivity) {
                    result = new IgnorePointer(
                        child: child,
                        ignoring: !visible
                        //todo : ignoringSemantics: !visible && !maintainSemantics, 
                    );
                }

                return new Opacity(
                    opacity: visible ? 1.0f : 0.0f,
                    //alwaysIncludeSemantics: maintainSemantics,
                    child: result
                );
            }

            D.assert(!maintainInteractivity);
            D.assert(!maintainSemantics);
            D.assert(!maintainSize);
            
            if (maintainState) {
                Widget result = child;
                if (!maintainAnimation) {
                    result = new TickerMode(child: child, enabled: visible);
                }

                return new Offstage(
                    child: result,
                    offstage: !visible
                );
            }
            D.assert(!maintainAnimation);
            D.assert(!maintainState);
            return visible ? child : replacement;
        }

        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add(new FlagProperty("visible", value: visible, ifFalse: "hidden", ifTrue: "visible"));
            properties.add(new FlagProperty("maintainState", value: maintainState, ifFalse: "maintainState"));
            properties.add(new FlagProperty("maintainAnimation", value: maintainAnimation,
                ifFalse: "maintainAnimation"));
            properties.add(new FlagProperty("maintainSize", value: maintainSize, ifFalse: "maintainSize"));
            properties.add(new FlagProperty("maintainSemantics", value: maintainSemantics, ifFalse: "maintainSemantics"));
            properties.add(new FlagProperty("maintainInteractivity", value: maintainInteractivity,
                ifFalse: "maintainInteractivity"));
        }
    }
    public class SliverVisibility : StatelessWidget {
        public SliverVisibility(
            Widget sliver,
            Widget replacementSliver,
            Key key = null,
            bool visible = true,
            bool maintainState = false,
            bool maintainAnimation = false,
            bool maintainSize = false,
            bool maintainInteractivity = false) : base (key: key) {
            replacementSliver = replacementSliver ?? new SliverToBoxAdapter();
            D.assert(sliver != null);
            D.assert(visible != null);
            D.assert(maintainState != null);
            D.assert(maintainAnimation != null);
            D.assert(maintainSize != null);
            D.assert(maintainInteractivity != null);
            D.assert(
                maintainState == true || maintainAnimation == false,
                ()=>"Cannot maintain animations if the state is not also maintained."
            );
            D.assert(
                maintainAnimation == true || maintainSize == false,
                ()=> "Cannot maintain size if animations are not maintained."
            );
            D.assert(
                maintainSize == true,
                ()=> "Cannot maintain semantics if size is not maintained."
            );
            D.assert(
                maintainSize == true || maintainInteractivity == false,
                ()=> "Cannot maintain interactivity if size is not maintained."
            );
            this.sliver = sliver;
            this.replacementSliver = replacementSliver;
            this.visible = visible;
            this.maintainState = maintainState;
            this.maintainAnimation = maintainAnimation;
            this.maintainSize = maintainSize;
            this.maintainInteractivity = maintainInteractivity;

        }


        public readonly Widget sliver;

        public readonly Widget replacementSliver;
        public readonly bool visible;
        public readonly bool maintainState;
        public readonly bool maintainAnimation; 
        public readonly bool maintainSize;
        public readonly bool maintainInteractivity;
        public override Widget build(BuildContext context) { 
            if (maintainSize) { 
                Widget result = sliver; 
                if (!maintainInteractivity) { 
                    result = new SliverIgnorePointer(
                        sliver: sliver,
                        ignoring: !visible
                    );
                } 
                return new SliverOpacity(
                    opacity: visible ? 1.0f : 0.0f,
                    sliver: result
                );
            }
            D.assert(!maintainInteractivity);
            D.assert(!maintainSize);
            if (maintainState) { 
                Widget result = sliver; 
                if (!maintainAnimation)
                    result = new TickerMode(child: sliver, enabled: visible); 
                return new SliverOffstage(
                    sliver: result,
                    offstage: !visible
                );
            }
            D.assert(!maintainAnimation);
            D.assert(!maintainState);
            return visible ? sliver : replacementSliver;
        }
        public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
            base.debugFillProperties(properties);
            properties.add( new FlagProperty("visible", value: visible, ifFalse: "hidden", ifTrue: "visible"));
            properties.add( new FlagProperty("maintainState", value: maintainState, ifFalse: "maintainState"));
            properties.add( new FlagProperty("maintainAnimation", value: maintainAnimation, ifFalse: "maintainAnimation"));
            properties.add( new FlagProperty("maintainSize", value: maintainSize, ifFalse: "maintainSize"));
            properties.add( new FlagProperty("maintainInteractivity", value: maintainInteractivity, ifFalse: "maintainInteractivity"));
        }
    }

    
}