Merge pull request #886 from Hixie/applyPaintTransform

applyPaintTransform() improvements

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

@@ -298,17 +298,18 @@ abstract class InkFeature {
     assert(referenceBox.attached);
     assert(!_debugDisposed);
     // find the chain of renderers from us to the feature's referenceBox
-    List<RenderBox> descendants = <RenderBox>[];
+    List<RenderBox> descendants = <RenderBox>[referenceBox];
     RenderBox node = referenceBox;
     while (node != renderer) {
-      descendants.add(node);
       node = node.parent;
       assert(node != null);
+      descendants.add(node);
     }
     // determine the transform that gets our coordinate system to be like theirs
     Matrix4 transform = new Matrix4.identity();
-    for (RenderBox descendant in descendants.reversed)
-      descendant.applyPaintTransform(transform);
+    assert(descendants.length >= 2);
+    for (int index = descendants.length - 1; index > 0; index -= 1)
+      descendants[index].applyPaintTransform(descendants[index - 1], transform);
     paintFeature(canvas, transform);
   }
 

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

@@ -420,12 +420,12 @@ class RenderBlockViewport extends RenderBlockBase {
     context.pushClipRect(needsCompositing, offset, Point.origin & size, _paintContents);
   }
 
-  void applyPaintTransform(Matrix4 transform) {
-    super.applyPaintTransform(transform);
+  void applyPaintTransform(RenderBox child, Matrix4 transform) {
     if (isVertical)
       transform.translate(0.0, startOffset);
     else
       transform.translate(startOffset, 0.0);
+    super.applyPaintTransform(child, transform);
   }
 
   bool hitTestChildren(HitTestResult result, { Point position }) {

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

@@ -609,49 +609,53 @@ abstract class RenderBox extends RenderObject {
   /// visually "on top" (i.e., paints later).
   bool hitTestChildren(HitTestResult result, { Point position }) => false;
 
-  /// Multiply the transform from the parent's coordinate system to this box's
-  /// coordinate system into the given transform
-  ///
-  /// This function is used to convert coordinate systems between boxes.
-  /// Subclasses that apply transforms during painting should override this
-  /// function to factor those transforms into the calculation.
-  void applyPaintTransform(Matrix4 transform) {
-    if (parentData is BoxParentData) {
-      Point position = (parentData as BoxParentData).position;
-      transform.translate(position.x, position.y);
-    }
-  }
-
   static Point _transformPoint(Matrix4 transform, Point point) {
     Vector3 position3 = new Vector3(point.x, point.y, 0.0);
     Vector3 transformed3 = transform.transform3(position3);
     return new Point(transformed3.x, transformed3.y);
   }
 
+  /// Multiply the transform from the parent's coordinate system to this box's
+  /// coordinate system into the given transform.
+  ///
+  /// This function is used to convert coordinate systems between boxes.
+  /// Subclasses that apply transforms during painting should override this
+  /// function to factor those transforms into the calculation.
+  ///
+  /// The RenderBox implementation takes care of adjusting the matrix for the
+  /// position of the given child.
+  void applyPaintTransform(RenderObject child, Matrix4 transform) {
+    assert(child.parent == this);
+    BoxParentData childParentData = child.parentData;
+    Point position = childParentData.position;
+    transform.translate(position.x, position.y);
+  }
+
   /// Convert the given point from the global coodinate system to the local
   /// coordinate system for this box
   Point globalToLocal(Point point) {
     assert(attached);
     Matrix4 transform = new Matrix4.identity();
     RenderObject renderer = this;
-    while (renderer != null) {
-      renderer.applyPaintTransform(transform);
-      renderer = renderer.parent;
+    while (renderer.parent is RenderObject) {
+      RenderObject rendererParent = renderer.parent;
+      rendererParent.applyPaintTransform(renderer, transform);
+      renderer = rendererParent;
     }
     /* double det = */ transform.invert();
     // TODO(abarth): Check the determinant for degeneracy.
     return _transformPoint(transform, point);
   }
 
-  /// Convert the given point from the local coordiante system for this box to
-  /// the global coordinate sytem
+  /// Convert the given point from the local coordinate system for this box to
+  /// the global coordinate system.
   Point localToGlobal(Point point) {
     List<RenderObject> renderers = <RenderObject>[];
     for (RenderObject renderer = this; renderer != null; renderer = renderer.parent)
       renderers.add(renderer);
     Matrix4 transform = new Matrix4.identity();
-    for (RenderObject renderer in renderers.reversed)
-      renderer.applyPaintTransform(transform);
+    for (int index = renderers.length - 1; index > 0; index -= 1)
+      renderers[index].applyPaintTransform(renderers[index - 1], transform);
     return _transformPoint(transform, point);
   }
 

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

@@ -1036,12 +1036,14 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
   /// be recorded on separate compositing layers.
   void paint(PaintingContext context, Offset offset) { }
 
-  /// If this render object applies a transform before painting, apply that
-  /// transform to the given matrix
+  /// Applies the transform that would be applied when painting the given child
+  /// to the given matrix.
   ///
   /// Used by coordinate conversion functions to translate coordinates local to
   /// one render object into coordinates local to another render object.
-  void applyPaintTransform(Matrix4 transform) { }
+  void applyPaintTransform(RenderObject child, Matrix4 transform) {
+    assert(child.parent == this);
+  }
 
 
   // EVENTS

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

@@ -974,9 +974,9 @@ class RenderTransform extends RenderProxyBox {
     }
   }
 
-  void applyPaintTransform(Matrix4 transform) {
-    super.applyPaintTransform(transform);
+  void applyPaintTransform(RenderBox child, Matrix4 transform) {
     transform.multiply(_effectiveTransform);
+    super.applyPaintTransform(child, transform);
   }
 
   void debugDescribeSettings(List<String> settings) {

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

@@ -164,9 +164,9 @@ class RenderViewport extends RenderBox with RenderObjectWithChildMixin<RenderBox
     }
   }
 
-  void applyPaintTransform(Matrix4 transform) {
-    super.applyPaintTransform(transform);
+  void applyPaintTransform(RenderBox child, Matrix4 transform) {
     transform.translate(-scrollOffset.dx, -scrollOffset.dy);
+    super.applyPaintTransform(child, transform);
   }
 
   bool hitTestChildren(HitTestResult result, { Point position }) {