Let synchronized painting generate correct paint invalidation rects

third_party/WebKit/Source/platform/graphics/paint/PaintController.h

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.h b/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
index 2e789edc90e4153587f76fda2c710013fb478f7d..9e3693fbd70b0a0889ca231e86d64c25f21c6915 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
@@ -43,7 +43,7 @@ public:
     }
 
     // These methods are called during paint invalidation (or paint if SlimmingPaintSynchronizedPainting is on).
-    void invalidate(const DisplayItemClientWrapper&, PaintInvalidationReason, const IntRect& previousPaintInvalidationRect, const IntRect& newPaintInvalidationRect);
+    void invalidate(const DisplayItemClientWrapper&, PaintInvalidationReason, const Vector<IntRect>& paintInvalidationRects);

[chrishtr, 2015/10/22 00:02:41]

If it's a vector, how is Walter's code supposed to know what the new bounds of
the display item are?

[Xianzhu, 2015/10/22 01:17:04]

This is a good question which actually answers my question about how
invalidation rects will be used.

Before this change, we also can't ensure newPaintInvalidationRect to be the
bounding box (see examples below).

We should separate paint invalidation rects from new bounds because not every
invalidation is a full invalidation. For example
- incremental invalidation: I had been thinking of removing it for spv2, but
based on today's discussion about raster invalidation, I think it's still useful
to keep raster invalidation small. (We'll need to keep also the original logics
to reduce rect-based invalidations e.g. [1].)
- rect based invalidations: LayoutObject::invalidatePaintRectangle();
- empty rect (or vector) passed when we just want to invalidate the display item
client.

We may have two methods for paint invalidation:
void invalidateDisplayItemClient(const DisplayItemClientWrapper&, const IntRect&
boundingBox);
void invalidateRect(PaintInvalidationReason, const IntRect& rect);

However, the above seem to only work with invalidation-in-paint because we must
know which PaintChunk the invalidated rect belongs to.

I have a much simpler method to make rect-based invalidation work for spv1
synchronized painting: use the whole original GraphicsLayer-based paint
invalidation. I'd like to leave PaintController rect-based invalidation to spv2.

[1]
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit....

     void invalidateUntracked(DisplayItemClient);
     void invalidateAll();