Paint tree logic for layout2.dart

sky/sdk/lib/framework/paint.dart

+library paint;
+
+class Matrix extends NativeFieldWrapperClass2 {
+  static final Matrix IDENTITY = new Matrix.transformation(1, 0, 0, 1, 0, 0);
+
+  // set a transformation
+  external Matrix.transformation(double a, double b, double c, double d, double e, double f);
+
+  // translate by dx,dy
+  external Matrix.translation(double dx, double dy);
+  external void translate(double dx, double dy);
+
+  // rotate theta radians clockwise around cx,cy
+  external Matrix.rotation(double cx, double cy, double theta);
+  external void rotate(double cx, double cy, double theta);
+
+  // ...
+}
+
+class Filter {
+  // ...
+}
+
+class Rect {
+  const Rect({ this.x, this.y, this.width, this.height });
+  final double x;
+  final double y;
+  final double width;
+  final double height;
+}
+
+class DisplayList extends NativeFieldWrapperClass2 {
+  // Wraps an SkPictureRecorder.
+  // All APIs throw once the recording has been ended.
+
+  DisplayList({ this.cullRect });
+  // Creates an SkPictureRecorder and starts recording.
+  // Note that Skia today assumes that the cullRect origin is (0,0),
+  // but this API does not (because we may want to draw outside a
+  // widget's bounds, inflating it on all sides, e.g. to draw a focus
+  // outline, but yet still put the widget top left at 0,0).
+
+  // Drawing commands outside these bounds (if set) may be optimised away.
+  // However, this is not guaranteed.
+  final Rect cullRect;
+
+  // Drawing API - circles, lines, rectangles, gradients, etc
+  // (defers to the canvas created when this class was instantiated)
+  // ...
+  external void pushTransform();
+  external Matrix get transform;
+  external void set transform (Matrix value);
+  external void popTransform();
+
+  external void drawPaintNode(PaintNode node, { Matrix transform: null, Filter filter: null });
+  // Inserts a PaintNode (i.e. SkDrawable) into the recording.
+  // assume: if (transform == null) transform = Matrix.IDENTITY;
+}
+
+class PaintNode extends NativeFieldWrapperClass2 {
+  // Wraps an SkDrawable.
+  // A PaintNode is inherently paintable, though that isn't exposed to
+  // the Dart side.
+
+  external setDisplayList(DisplayList picture);
+  // Ends picture's recording and updates the SkDrawable to that new
+  // picture, notifying the C++ side of the change so that the next
+  // time we paint, we use this new picture.
+}
+
+external PaintNode rootPaintNode;