Attempt to write a RenderShadowedBox

sky/sdk/lib/framework/rendering/render_box.dart

Index: sky/sdk/lib/framework/rendering/render_box.dart
diff --git a/sky/sdk/lib/framework/rendering/render_box.dart b/sky/sdk/lib/framework/rendering/render_box.dart
index dc081e1a159a7a21d7e1af6fa23f2e51bc3839a0..1d1f9bb04746f73a246e90b92eedd36a9d8fb5ca 100644
--- a/sky/sdk/lib/framework/rendering/render_box.dart
+++ b/sky/sdk/lib/framework/rendering/render_box.dart
@@ -145,7 +145,7 @@ class RenderSizedBox extends RenderProxyBox {
   final sky.Size desiredSize;
 
   RenderSizedBox({
-    RenderBox child, 
+    RenderBox child,
     this.desiredSize: const sky.Size.infinite()
   }) : super(child);
 
@@ -261,6 +261,58 @@ class RenderDecoratedBox extends RenderProxyBox {
 
 }
 
+// This must be immutable, because we won't notice when it changes
+class BoxShadow {
+  const BoxShadow({
+    this.color,
+    this.offset
+  });
+
+  final sky.Size offset;
+  final sky.Color color;
+}
+
+class RenderShadowedBox extends RenderProxyBox {
+
+  RenderShadowedBox({
+    BoxShadow shadow,
+    RenderBox child
+  }) : _shadow = shadow, super(child);
+
+  BoxShadow _shadow;
+  BoxShadow get shadow => _decoration;

[Matt Perry, 2015/06/02 20:57:37]

Did you mean to return _shadow here?

+  void set shadow (BoxShadow value) {
+    if (value == _shadow)
+      return;
+    _shadow = value;
+    markNeedsPaint();
+  }
+
+  sky.Paint _createShadowPaint(BoxShadow shadow) {
+    sky.Paint paint = new sky.Paint()..color = shadow.color;

[Matt Perry, 2015/06/02 20:57:36]

This should be the color of the Main layer, not the shadow.

+    sky.Size offset = shadow.offset;
+    var builder = new sky.LayerDrawLooperBuilder()
+      // Shadow layer.
+      ..addLayerOnTop(
+          new sky.DrawLooperLayerInfo()
+            ..setOffset(offset.toPoint())
+            ..setColorMode(sky.TransferMode.srcInMode),

[Matt Perry, 2015/06/02 21:19:01]

BTW, the existing code[1] uses srcMode. We might want to use that here.

[1]
https://github.com/domokit/mojo/blob/2aad0d73122aca64491b96c69530578e6f0d81fd...

+          (sky.Paint layerPaint) {
+        layerPaint.setARGB(128, 55, 55, 55);

[Matt Perry, 2015/06/02 20:57:36]

This is the shadow color. Since we're using TransferMode.srcInMode, the
layerPaint.color here overrides paint.color.

+        // TODO(mpcomplete): add blur filter
+      })
+      // Main layer.
+      ..addLayerOnTop(new sky.DrawLooperLayerInfo(), (_) {});
+    paint.setDrawLooper(builder.build());
+    return paint;
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    sky.Paint paint = _createShadowPaint(_shadow);
+    canvas.drawRect(new sky.Rect.fromLTRB(0.0, 0.0, size.width, size.height), paint);
+    super.paint(canvas);
+  }
+}
 
 // RENDER VIEW LAYOUT MANAGER