Clamps to invalidation region of a PictureLayer to the layer bounds to avoid adding unecessary bulk

cc/picture_layer.cc

Index: cc/picture_layer.cc
diff --git a/cc/picture_layer.cc b/cc/picture_layer.cc
index 4f192da7e180fdb51eaa7071aaad1d5107143fce..15a61705f177e2ed1f7bfadb6930c7dc922736f3 100644
--- a/cc/picture_layer.cc
+++ b/cc/picture_layer.cc
@@ -51,7 +51,11 @@ void PictureLayer::setLayerTreeHost(LayerTreeHost* host) {
 
 void PictureLayer::setNeedsDisplayRect(const gfx::RectF& layer_rect) {
   gfx::Rect rect = gfx::ToEnclosedRect(layer_rect);
-  pending_invalidation_.Union(rect);
+  if (!rect.IsEmpty()) {

[danakj, 2013/01/09 01:00:05]

i think this if() is kinda surplus too, everything should be no-ops without it
when the rect is empty, unless we're seeing some perf hit from this (seems
unlikely in this method?)

[vangelis, 2013/01/09 01:50:36]

it is indeed a no-op but still goes though a surprising amount of code through
SkRegion with several on-stack allocations. This method gets called quite a bit
with empty rects, when the assorted layer properties are being setup. Probably
not a significant win perf-wise but since I was passing by...

[danakj, 2013/01/09 01:51:48]

If it's an issue, maybe we should add it to cc::Region instead, so all callsites
can benefit? I'll leave that up to you.

+    // Clamp invalidation to the layer bounds.
+    rect.Intersect(gfx::Rect(contentBounds()));

[danakj, 2013/01/09 01:00:05]

Sorry to miss this last round: You want bounds() here actually, not
contentBounds(). This is all in layer space (hence layer_rect's name)

[vangelis, 2013/01/09 01:50:36]

Done.

+    pending_invalidation_.Union(rect);
+  }
   Layer::setNeedsDisplayRect(layer_rect);
 }