Implement ClipRRect

sky/sdk/lib/README.md

Index: sky/sdk/lib/README.md
diff --git a/sky/sdk/lib/README.md b/sky/sdk/lib/README.md
index 3bfbfbf49fafadb24c6d1b777e22e145b552fe36..30406045934ce1fe3bfe6441fbdaa0ce35b97b21 100644
--- a/sky/sdk/lib/README.md
+++ b/sky/sdk/lib/README.md
@@ -63,3 +63,16 @@ Here is a diagram summarising all this:
     +-----------------------------+ -------
 
 TODO(ianh): document dart:sky and the Host APIs somewhere
+
+Sky Engine API
+--------------
+
+The Sky engine API provides effecient, immutable wrappers
+for common Skia C++ types, notably Color, Point, and Rect.
+Because these wrappers are immutable, they are suitable
+for storage in final member variables of widget classes.
+More complex Skia wrappers such as Paint and RRect are
+mutable, to more closely match the Skia APIs. We recommend
+constructing wrappers for complex Skia classes dynamically
+during the painting phase based on the underlying state of
+the widget.

[abarth-chromium, 2015/06/25 18:04:12]

This text is good, but I'm not sure this is the right README file for it.  This
doc is pretty high-level and this text is pretty specific...  Maybe create a
README.md in sky/sdk/lib/painting with this text?  That way the
painting/README.md can grow to be all about the painting aspects of the system.

[Hixie, 2015/06/25 18:22:36]

Yeah we weren't sure where to put it. We considered painting/ first, actually,
but it's not really the place to decument the dart:sky API (which is what this
is).

I suggested to Collin that we put it in this README for now and that once this
section grew big enough we'd split it into a separate SKYENGINE.md file or some
such.

[abarth-chromium, 2015/06/25 18:34:01]

Yeah, we're clearly going to need docs for all the dart:sky APIs, and you're
right that this belongs with that more than lib/painting.

I'm fine with this text being here until we've got a better home for it.