Instead of applying a transform for every RenderObject, pass down an Offset for where to paint.

sky/engine/core/painting/Rect.dart

Index: sky/engine/core/painting/Rect.dart
diff --git a/sky/engine/core/painting/Rect.dart b/sky/engine/core/painting/Rect.dart
index 0fc67baf296e63fb969d6af75e8679217315da21..75dd303996ce93bd7e78fafe0468be708263e2c4 100644
--- a/sky/engine/core/painting/Rect.dart
+++ b/sky/engine/core/painting/Rect.dart
@@ -16,6 +16,14 @@ class Rect {
       ..[3] = bottom;
   }
 
+  Rect.fromLTWH(double left, double top, double width, double height) {
+    _value
+      ..[0] = left
+      ..[1] = top
+      ..[2] = left + width
+      ..[3] = top + height;
+  }
+
   Rect.fromPointAndSize(Point point, Size size) {
     _value
       ..[0] = point.x