Merge pull request #617 from abarth/separate_offset_and_size

Separate the notions of offset and size in compositing

sky/packages/sky/lib/rendering/box.dart

@@ -1751,10 +1751,8 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     try {
       final double devicePixelRatio = sky.view.devicePixelRatio;
       Matrix4 transform = new Matrix4.diagonal3Values(devicePixelRatio, devicePixelRatio, 1.0);
-      Rect bounds = Point.origin & size;
-      Rect scaledBounds = Point.origin & (size * devicePixelRatio);
-      _rootLayer = new TransformLayer(bounds: scaledBounds, transform: transform);
-      PaintingContext context = new PaintingContext(bounds);
+      _rootLayer = new TransformLayer(transform: transform);
+      PaintingContext context = new PaintingContext(Offset.zero, size);
       _rootLayer.add(context.layer);
       context.paintChild(child, Point.origin);
       context.endRecording();
@@ -1767,7 +1765,7 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     sky.tracing.begin('RenderView.compositeFrame');
     try {
       sky.PictureRecorder recorder = new sky.PictureRecorder();
-      sky.Canvas canvas = new sky.Canvas(recorder, _rootLayer.bounds);
+      sky.Canvas canvas = new sky.Canvas(recorder, Point.origin & (size * sky.view.devicePixelRatio));
       _rootLayer.paint(canvas);
       sky.view.picture = recorder.endRecording();
     } finally {

sky/packages/sky/lib/rendering/layer.dart

@@ -8,9 +8,9 @@ import 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 import 'package:vector_math/vector_math.dart';
 
 abstract class Layer {
-  Layer({ this.bounds });
+  Layer({ this.offset: Offset.zero });
 
-  Rect bounds;
+  Offset offset; // From parent, in parent's coordinate system.
 
   ContainerLayer _parent;
   ContainerLayer get parent => _parent;
@@ -30,18 +30,21 @@ abstract class Layer {
 }
 
 class PictureLayer extends Layer {
-  PictureLayer({ Rect bounds })
-    : super(bounds: bounds);
+  PictureLayer({ Offset offset: Offset.zero, this.size })
+    : super(offset: offset);
 
+  Size size;
   sky.Picture picture;
 
   void paint(sky.Canvas canvas) {
+    canvas.translate(offset.dx, offset.dy);
     canvas.drawPicture(picture);
+    canvas.translate(-offset.dx, -offset.dy);
   }
 }
 
 class ContainerLayer extends Layer {
-  ContainerLayer({ Rect bounds }) : super(bounds: bounds);
+  ContainerLayer({ Offset offset: Offset.zero }) : super(offset: offset);
 
   void paint(sky.Canvas canvas) {
     Layer child = firstChild;
@@ -133,12 +136,13 @@ class ContainerLayer extends Layer {
 }
 
 class TransformLayer extends ContainerLayer {
-  TransformLayer({ this.transform, Rect bounds }) : super(bounds: bounds);
+  TransformLayer({ Offset offset: Offset.zero, this.transform }) : super(offset: offset);
 
   Matrix4 transform;
 
   void paint(sky.Canvas canvas) {
     canvas.save();
+    canvas.translate(offset.dx, offset.dy);
     canvas.concat(transform.storage);
     super.paint(canvas);
     canvas.restore();
@@ -146,11 +150,14 @@ class TransformLayer extends ContainerLayer {
 }
 
 class ClipLayer extends ContainerLayer {
-  ClipLayer({ Rect bounds }) : super(bounds: bounds);
+  ClipLayer({ Offset offset: Offset.zero, this.size }) : super(offset: offset);
+
+  Size size;
 
   void paint(sky.Canvas canvas) {
     canvas.save();
-    canvas.clipRect(bounds);
+    canvas.translate(offset.dx, offset.dy);
+    canvas.clipRect(Point.origin & size);
     super.paint(canvas);
     canvas.restore();
   }
@@ -158,11 +165,13 @@ class ClipLayer extends ContainerLayer {
 
 class ColorFilterLayer extends ContainerLayer {
   ColorFilterLayer({
-    Rect bounds,
+    Offset offset: Offset.zero,
+    this.size,
     this.color,
     this.transferMode
-  }) : super(bounds: bounds);
+  }) : super(offset: offset);
 
+  Size size;
   Color color;
   sky.TransferMode transferMode;
 
@@ -171,7 +180,8 @@ class ColorFilterLayer extends ContainerLayer {
       ..color = color
       ..setTransferMode(transferMode);
 
-    canvas.saveLayer(bounds, paint);
+    canvas.saveLayer(offset & size, paint);
+    canvas.translate(offset.dx, offset.dy);
     super.paint(canvas);
     canvas.restore();
   }

sky/packages/sky/lib/rendering/object.dart

@@ -40,19 +40,19 @@ class PaintingContext {
 
   sky.PictureRecorder _recorder;
 
-  PaintingContext(Rect bounds) {
-    _startRecording(bounds);
+  PaintingContext(Offset offest, Size size) {
+    _startRecording(offest, size);
   }
 
   PaintingContext.forTesting(this.canvas);
 
-  void _startRecording(Rect bounds) {
+  void _startRecording(Offset offset, Size size) {
     assert(_layer == null);
     assert(_recorder == null);
     assert(canvas == null);
-    _layer = new PictureLayer(bounds: bounds);
+    _layer = new PictureLayer(offset: offset, size: size);
     _recorder = new sky.PictureRecorder();
-    canvas = new PaintingCanvas(_recorder, bounds);
+    canvas = new PaintingCanvas(_recorder, Point.origin & size);
   }
 
   void endRecording() {
@@ -70,18 +70,23 @@ class PaintingContext {
 
     if (!child.requiresCompositing)
       return child._paintWithContext(this, offset);
+    _compositChild(child, offset, layer.parent, layer.nextSibling);
+  }
 
-    final Layer originalLayer = layer;
+  void _compositChild(RenderObject child, Offset offset, ContainerLayer parentLayer, Layer nextSibling) {
+    final PictureLayer originalLayer = _layer;
     endRecording();
 
-    Rect bounds = child.paintBounds.shift(offset);
-    PaintingContext context = new PaintingContext(bounds);
-    originalLayer.parent.add(context.layer, before: originalLayer.nextSibling);
-    child._paintWithContext(context, Offset.zero);
-    context.endRecording();
+    Rect childBounds = child.paintBounds;
+    Offset childOffset = childBounds.topLeft.toOffset();
+    PaintingContext context = new PaintingContext(offset + childOffset, childBounds.size);
+    parentLayer.add(context.layer, before: nextSibling);
+    child._layer = context.layer;
+    child._paintWithContext(context, -childOffset);
 
-    _startRecording(originalLayer.bounds);
+    _startRecording(originalLayer.offset, originalLayer.size);
     originalLayer.parent.add(layer, before: context.layer.nextSibling);
+    context.endRecording();
   }
 }
 
@@ -411,7 +416,9 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     assert(!_needsLayout);
     assert(requiresCompositing);
     assert(_layer != null);
-    PaintingContext context = new PaintingContext(paintBounds);
+    // TODO(abarth): Using _layer.offset isn't correct if the topLeft of our
+    // paint bounds has changed since our last repaint.
+    PaintingContext context = new PaintingContext(_layer.offset, paintBounds.size);
     _layer.parent.add(context.layer, before: _layer);
     _layer.detach();
     _layer = context._layer;