[Webkit-unassigned] [Bug 71972] Consider all RenderObjects in a GraphicsLayer when marking opaque

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=71972





--- Comment #4 from Dana Jansens <danakj at chromium.org>  2011-11-22 12:58:06 PST ---
Here's how I think we could approach considering all RenderObjects in a RLBacking.  The key ideas behind the code are:

1) RO::layout() is problematic to hop on, since it does partial tree walks. To build the full Region requires walking through a Rect for each RO anyway.

2) The RL's opaque region should depend on its scroll offset, and change when a scroll happens.

3) I chose RL::computeRepaintRects() to compute the opaque region since it is executed after scrolling, and recomputes various other painting bounds.

4) It walks the tree of ROs for a single RL.  Considers only ROs that are visible after scrolling.  Constructs a Region from the opaque ones.  If the box decorations area is opaque but contents area is not, it also checks if ROs in its subtree fill its contents area.

Includes a LayoutTest with scrolling to verify the code is working, and tests for RO children which are divs or images.

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