Implement text shadow.

Runtime/painting/text_style.cs

         public readonly Paint foreground;
         public readonly Paint background;
         public readonly string fontFamily;
+        public readonly List<BoxShadow> shadows;
 
         public List<string> fontFamilyFallback {
             get { return this._fontFamilyFallback; }
             float? decorationThickness = null,
             string fontFamily = null,
             List<string> fontFamilyFallback = null,
+            List<BoxShadow> shadows = null,
             string debugLabel = null) {
             D.assert(color == null || foreground == null, () => _kColorForegroundWarning);
             D.assert(backgroundColor == null || background == null, () => _kColorBackgroundWarning);
             this.debugLabel = debugLabel;
             this.foreground = foreground;
             this.background = background;
+            this.shadows = shadows;
-            if (this.inherit != other.inherit || this.fontFamily != other.fontFamily
-                                              || this.fontSize != other.fontSize || this.fontWeight != other.fontWeight
-                                              || this.fontStyle != other.fontStyle ||
-                                              this.letterSpacing != other.letterSpacing
-                                              || this.wordSpacing != other.wordSpacing ||
-                                              this.textBaseline != other.textBaseline
-                                              || this.height != other.height || this.background != other.background) {
+            if (this.inherit != other.inherit || this.fontFamily != other.fontFamily ||
+                this.fontSize != other.fontSize || this.fontWeight != other.fontWeight ||
+                this.fontStyle != other.fontStyle || this.letterSpacing != other.letterSpacing ||
+                this.wordSpacing != other.wordSpacing || this.textBaseline != other.textBaseline ||
+                this.height != other.height || this.background != other.background ||
+                this.shadows.equalsList(other.shadows)) {
-                this.decorationColor != other.decorationColor
-                || this.decorationStyle != other.decorationStyle) {
+                this.decorationColor != other.decorationColor ||
+                this.decorationStyle != other.decorationStyle) {
                 return RenderComparison.paint;
             }
 
             float decorationThicknessDelta = 0.0f,
             string fontFamily = null,
             List<string> fontFamilyFallback = null,
+            List<BoxShadow> shadows = null,
             float fontSizeFactor = 1.0f,
             float fontSizeDelta = 0.0f,
             int fontWeightDelta = 0,
                 decorationThickness: this.decorationThickness == null
                     ? null
                     : this.decorationThickness * decorationThicknessFactor + decorationThicknessDelta,
+                shadows: shadows ?? this.shadows,
                 debugLabel: modifiedDebugLabel
             );
         }
                 decorationColor: other.decorationColor,
                 decorationStyle: other.decorationStyle,
                 decorationThickness: other.decorationThickness,
+                shadows: other.shadows,
                 debugLabel: mergedDebugLabel
             );
         }
             Color decorationColor = null,
             TextDecorationStyle? decorationStyle = null,
             float? decorationThickness = null,
+            List<BoxShadow> shadows = null,
             string debugLabel = null) {
             D.assert(color == null || foreground == null, () => _kColorForegroundWarning);
             D.assert(backgroundColor == null || background == null, () => _kColorBackgroundWarning);
                 decorationThickness: decorationThickness ?? this.decorationThickness,
                 foreground: foreground ?? this.foreground,
                 background: background ?? this.background,
+                shadows: shadows ?? this.shadows,
                 debugLabel: newDebugLabel
             );
         }
                     decorationColor: Color.lerp(null, b.decorationColor, t),
                     decorationStyle: t < 0.5f ? null : b.decorationStyle,
                     decorationThickness: t < 0.5f ? null : b.decorationThickness,
+                    shadows: t < 0.5f ? null : b.shadows,
                     debugLabel: lerpDebugLabel
                 );
             }
                     decorationColor: Color.lerp(a.decorationColor, null, t),
                     decorationStyle: t < 0.5f ? a.decorationStyle : null,
                     decorationThickness: t < 0.5f ? a.decorationThickness : null,
+                    shadows: t < 0.5f ? a.shadows : null,
                     debugLabel: lerpDebugLabel
                 );
             }
                 decorationThickness: MathUtils.lerpFloat(
                     a.decorationThickness ?? b.decorationThickness ?? 0.0f,
                     b.decorationThickness ?? a.decorationThickness ?? 0.0f, t),
+                shadows: t < 0.5f ? a.shadows : b.shadows,
                 debugLabel: lerpDebugLabel
             );
         }
                    this.decorationThickness == other.decorationThickness &&
                    Equals(this.foreground, other.foreground) &&
                    Equals(this.background, other.background) &&
-                   CollectionUtils.equalsList(this.fontFamilyFallback, other.fontFamilyFallback) &&
+                   this.fontFamilyFallback.equalsList(other.fontFamilyFallback) &&
+                   this.shadows.equalsList(other.shadows) &&
                    string.Equals(this.fontFamily, other.fontFamily);
         }
 
                 hashCode = (hashCode * 397) ^ (this.fontFamily != null ? this.fontFamily.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^
                            (this.fontFamilyFallback != null ? this.fontFamilyFallback.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ (this.shadows != null ? this.shadows.GetHashCode() : 0);
                 return hashCode;
             }
         }

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_impl.cs

                     }
 
                     case DrawTextBlob cmd: {
+                        this._paintTextShadow(cmd.textBlob, cmd.offset);
                         this._drawTextBlob(cmd.textBlob, (uiOffset.fromOffset(cmd.offset)).Value,
                             uiPaint.fromPaint(cmd.paint));
                         break;
                     }
 
                     case uiDrawTextBlob cmd: {
+                        this._paintTextShadow(cmd.textBlob, new Offset(cmd.offset.Value.dx, cmd.offset.Value.dy));
                         this._drawTextBlob(cmd.textBlob, cmd.offset.Value, cmd.paint);
                         break;
                     }
 
             if (needsSave) {
                 this._restore();
+            }
+        }
+
+        void _paintTextShadow(TextBlob? textBlob, Offset offset) {
+            D.assert(textBlob != null);
+            if (textBlob.Value.style.shadows != null && textBlob.Value.style.shadows.isNotEmpty()) {
+                textBlob.Value.style.shadows.ForEach(shadow => {
+                    Paint paint = new Paint {
+                        color = shadow.color,
+                        maskFilter = shadow.blurRadius != 0
+                            ? MaskFilter.blur(BlurStyle.normal, shadow.blurRadius)
+                            : null,
+                    };
+                    this._drawTextBlob(textBlob, uiOffset.fromOffset(shadow.offset + offset).Value,
+                        uiPaint.fromPaint(paint));
+                });
             }
         }
 
             }
 
             this._drawTextDrawMeshCallback(paint, null, null, false, 0, 0, tex, textBlobBounds, mesh, notEmoji);
+            
         }
 
         public void flush(uiPicture picture) {

Runtime/ui/text.cs

 using System;
 using System.Collections.Generic;
+using System.Collections.Specialized;
+using Unity.UIWidgets.foundation;
 using Unity.UIWidgets.painting;
 
 namespace Unity.UIWidgets.ui {
         public readonly string fontFamily = kDefaultFontFamily;
         public readonly Paint foreground;
         public readonly Paint background;
+        public readonly List<BoxShadow> shadows;
 
         internal UnityEngine.Color UnityColor {
             get { return this.color.toColor(); }
                     decorationColor: style.decorationColor ?? currentStyle.decorationColor,
                     fontFamily: style.fontFamily ?? currentStyle.fontFamily,
                     foreground: style.foreground ?? currentStyle.foreground,
-                    background: style.background ?? currentStyle.background
+                    background: style.background ?? currentStyle.background,
+                    shadows: style.shadows ?? currentStyle.shadows
                 );
             }
 
                 decorationColor: style.decorationColor,
                 fontFamily: style.fontFamily,
                 foreground: style.foreground,
-                background: style.background
+                background: style.background,
+                shadows: style.shadows
             );
         }
 
                    Equals(this.decoration, other.decoration) &&
                    Equals(this.decorationColor, other.decorationColor) &&
                    this.decorationStyle == other.decorationStyle &&
-                   string.Equals(this.fontFamily, other.fontFamily);
+                   string.Equals(this.fontFamily, other.fontFamily) &&
+                   this.shadows.equalsList(other.shadows);
         }
 
         public override bool Equals(object obj) {
                 hashCode = (hashCode * 397) ^ (this.decorationColor != null ? this.decorationColor.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ this.decorationStyle.GetHashCode();
                 hashCode = (hashCode * 397) ^ (this.fontFamily != null ? this.fontFamily.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ (this.shadows != null ? this.shadows.GetHashCode() : 0);
                 return hashCode;
             }
         }
         }
 
 
-        public TextStyle(Color color = null, float? fontSize = null,
-            FontWeight fontWeight = null, FontStyle? fontStyle = null, float? letterSpacing = null,
-            float? wordSpacing = null, TextBaseline? textBaseline = null, float? height = null,
-            TextDecoration decoration = null, TextDecorationStyle? decorationStyle = null, Color decorationColor = null,
+        public TextStyle(Color color = null,
+            float? fontSize = null,
+            FontWeight fontWeight = null,
+            FontStyle? fontStyle = null,
+            float? letterSpacing = null,
+            float? wordSpacing = null,
+            TextBaseline? textBaseline = null,
+            float? height = null,
+            TextDecoration decoration = null,
+            TextDecorationStyle? decorationStyle = null,
+            Color decorationColor = null,
-            Paint background = null
+            Paint background = null,
+            List<BoxShadow> shadows = null
         ) {
             this.color = color ?? this.color;
             this.fontSize = fontSize ?? this.fontSize;
             this.fontFamily = fontFamily ?? this.fontFamily;
             this.foreground = foreground ?? this.foreground;
             this.background = background ?? this.background;
+            this.shadows = shadows ?? this.shadows;
         }
     }