Implement ClipRRect

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1206373002.

sdk/lib/README.md

@@ -63,3 +63,16 @@ Here is a diagram summarising all this:
     +-----------------------------+ -------
 
 TODO(ianh): document dart:sky and the Host APIs somewhere
+
+Sky Engine API
+--------------
+
+The Sky engine API provides efficient, immutable wrappers
+for common Skia C++ types, notably Color, Point, and Rect.
+Because these wrappers are immutable, they are suitable
+for storage in final member variables of widget classes.
+More complex Skia wrappers such as Paint and RRect are
+mutable, to more closely match the Skia APIs. We recommend
+constructing wrappers for complex Skia classes dynamically
+during the painting phase based on the underlying state of
+the widget.

sdk/lib/rendering/box.dart

@@ -589,6 +589,45 @@ class RenderClipRect extends RenderProxyBox {
   }
 }
 
+class RenderClipRRect extends RenderProxyBox {
+  RenderClipRRect({ RenderBox child, double xRadius, double yRadius })
+    : _xRadius = xRadius, _yRadius = yRadius, super(child) {
+    assert(_xRadius != null);
+    assert(_yRadius != null);
+  }
+
+  double _xRadius;
+  double get xRadius => _xRadius;
+  void set xRadius (double value) {
+    assert(value != null);
+    if (_xRadius == value)
+      return;
+    _xRadius = value;
+    markNeedsPaint();
+  }
+
+  double _yRadius;
+  double get yRadius => _yRadius;
+  void set yRadius (double value) {
+    assert(value != null);
+    if (_yRadius == value)
+      return;
+    _yRadius = value;
+    markNeedsPaint();
+  }
+
+  void paint(RenderCanvas canvas) {
+    if (child != null) {
+      Rect rect = new Rect.fromSize(size);
+      canvas.saveLayer(rect, new Paint());
+      sky.RRect rrect = new sky.RRect()..setRectXY(rect, xRadius, yRadius);
+      canvas.clipRRect(rrect);
+      child.paint(canvas);
+      canvas.restore();
+    }
+  }
+}
+
 class RenderClipOval extends RenderProxyBox {
   RenderClipOval({ RenderBox child }) : super(child);
 

sdk/lib/widgets/basic.dart

@@ -104,6 +104,24 @@ class ClipRect extends OneChildRenderObjectWrapper {
 
   RenderClipRect get root => super.root;
   RenderClipRect createNode() => new RenderClipRect();
+
+  // Nothing to sync, so we don't implement syncRenderObject()
+}
+
+class ClipRRect extends OneChildRenderObjectWrapper {
+  final double xRadius;
+  final double yRadius;
+  ClipRRect({ String key, Widget child, this.xRadius, this.yRadius })
+    : super(key: key, child: child);
+
+  RenderClipRRect get root => super.root;
+  RenderClipRRect createNode() => new RenderClipRRect(xRadius: xRadius, yRadius: yRadius);
+
+  void syncRenderObject(ClipRRect old) {
+    super.syncRenderObject(old);
+    root.xRadius = xRadius;
+    root.yRadius = yRadius;
+  }
 }
 
 class ClipOval extends OneChildRenderObjectWrapper {
@@ -112,8 +130,9 @@ class ClipOval extends OneChildRenderObjectWrapper {
 
   RenderClipOval get root => super.root;
   RenderClipOval createNode() => new RenderClipOval();
-}
 
+  // Nothing to sync, so we don't implement syncRenderObject()
+}
 
 // POSITIONING AND SIZING NODES
 
@@ -157,6 +176,8 @@ class Center extends OneChildRenderObjectWrapper {
 
   RenderPositionedBox get root => super.root;
   RenderPositionedBox createNode() => new RenderPositionedBox();
+
+  // Nothing to sync, so we don't implement syncRenderObject()
 }
 
 class SizedBox extends OneChildRenderObjectWrapper {