Render Material using a PhysicalModel with optional compositing (#8920)

packages/flutter/lib/src/material/material.dart

@@ -7,7 +7,6 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 import 'constants.dart';
-import 'shadows.dart';
 import 'theme.dart';
 
 /// Signature for the callback used by ink effects to obtain the rectangle for the effect.
@@ -228,14 +227,33 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
         vsync: this,
       )
     );
+
     if (config.type == MaterialType.circle) {
-      contents = new ClipOval(child: contents);
-    } else if (kMaterialEdges[config.type] != null) {
-      contents = new ClipRRect(
-        borderRadius: radius,
-        child: contents
+      contents = new PhysicalModel(
+        shape: BoxShape.circle,
+        elevation: config.elevation,
+        color: backgroundColor,
+        child: contents,
+      );
+    } else if (config.type == MaterialType.transparency) {
+      if (radius == null) {
+        contents = new ClipRect(child: contents);
+      } else {
+        contents = new ClipRRect(
+          borderRadius: radius,
+          child: contents
+        );
+      }
+    } else {
+      contents = new PhysicalModel(
+        shape: BoxShape.rectangle,
+        borderRadius: radius ?? BorderRadius.zero,
+        elevation: config.elevation,
+        color: backgroundColor,
+        child: contents,
       );
     }
+
     if (config.type != MaterialType.transparency) {
       contents = new AnimatedContainer(
         curve: Curves.fastOutSlowIn,
@@ -247,7 +265,6 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
         child: new Container(
           decoration: new BoxDecoration(
             borderRadius: radius,
-            boxShadow: config.elevation == 0 ? null : kElevationToShadow[config.elevation],
             backgroundColor: backgroundColor,
             shape: config.type == MaterialType.circle ? BoxShape.circle : BoxShape.rectangle
           ),

packages/flutter/lib/src/rendering/object.dart

@@ -442,19 +442,35 @@ class PaintingContext {
   /// * `color` is the background color.
   /// * `painter` is a callback that will paint with the `clipRRect` applied. This
   ///   function calls the `painter` synchronously.
-  void pushPhysicalModel(Offset offset, Rect bounds, RRect clipRRect, int elevation, Color color, PaintingContextCallback painter) {
+  void pushPhysicalModel(bool needsCompositing, Offset offset, Rect bounds, RRect clipRRect, int elevation, Color color, PaintingContextCallback painter) {
     final Rect offsetBounds = bounds.shift(offset);
     final RRect offsetClipRRect = clipRRect.shift(offset);
-    _stopRecordingIfNeeded();
-    final PhysicalModelLayer physicalModel = new PhysicalModelLayer(
-      clipRRect: offsetClipRRect,
-      elevation: elevation,
-      color: color,
-    );
-    _appendLayer(physicalModel);
-    final PaintingContext childContext = new PaintingContext._(physicalModel, offsetBounds);
-    painter(childContext, offset);
-    childContext._stopRecordingIfNeeded();
+    if (needsCompositing) {
+      _stopRecordingIfNeeded();
+      final PhysicalModelLayer physicalModel = new PhysicalModelLayer(
+        clipRRect: offsetClipRRect,
+        elevation: elevation,
+        color: color,
+      );
+      _appendLayer(physicalModel);
+      final PaintingContext childContext = new PaintingContext._(physicalModel, offsetBounds);
+      painter(childContext, offset);
+      childContext._stopRecordingIfNeeded();
+    } else {
+      if (elevation != 0) {
+        canvas.drawShadow(
+          new Path()..addRRect(offsetClipRRect),
+          const Color(0xFF000000),
+          elevation,
+          color.alpha != 0xFF,
+        );
+      }
+      canvas.drawRRect(offsetClipRRect, new Paint()..color=color);
+      canvas.saveLayer(offsetBounds, _defaultPaint);
+      canvas.clipRRect(offsetClipRRect);
+      painter(this, offset);
+      canvas.restore();
+    }
   }
 }
 

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -1210,9 +1210,6 @@ class RenderPhysicalModel extends _RenderCustomClip<RRect> {
       assert(_borderRadius != null);
   }
 
-  @override
-  bool get alwaysNeedsCompositing => true;
-
   /// The shape of the layer.
   BoxShape get shape => _shape;
   BoxShape _shape;
@@ -1285,7 +1282,7 @@ class RenderPhysicalModel extends _RenderCustomClip<RRect> {
   void paint(PaintingContext context, Offset offset) {
     if (child != null) {
       _updateClip();
-      context.pushPhysicalModel(offset, _clip.outerRect, _clip, _elevation, _color, super.paint);
+      context.pushPhysicalModel(needsCompositing, offset, _clip.outerRect, _clip, _elevation, _color, super.paint);
     }
   }
 }