Bug 82997 – [chromium] Fix layer sorting perspective w if w becomes negative

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Shawn Singh]

A follow-up to https://bugs.webkit.org/show_bug.cgi?id=80806

There are still some minor flashing/sorting artifacts that occur that are most likely to to this issue.

[Shawn Singh]

So here's the situation:

I was able to whip up a quick fix for this, and it did fix the flashing sorting artifacts that we were seeing:
   - css space cube demo
   - mozilla cardboard box + paper sheep demo

However, the fix as I've hacked it currently, uses only a sub-portion of the clipped geometry to do layer sorting.  (so that I can still use FloatQuad instead of the clipped polygon).

Of course, this causes other potential layer sorting bugs, for example, it regresses acko.net to have flaky sorting again.


There are two options I can think of to fix this:

(1) make layer sorter work with general clipped polygons of up to 8 vertices.  We can create a quick data structure, ClippedQuad, that internally holds up to 8 vertices without using the allocator.

(2) make layer sorter support multiple quads per layer and accumulate all topological dependencies for all quads.

Any preferences?   At the moment it seems like #2 will be easier to implement.

[Shawn Singh]

(In reply to comment #1)

> Of course, this causes other potential layer sorting bugs, for example, it regresses acko.net to have flaky sorting again.
> 

Actually, those acko.net sorting bugs already existed, even before the previous perspective clipping patch.  So my fix should be OK without forcing more complexity.

[Shawn Singh]

Created attachment 136096 [details]
Working fix, without unit test yet

[Shawn Singh]

Created attachment 136184 [details]
Patch with unit test

Shuffled around some CCMathUtil code at the same time, for cleanliness

[Adrienne Walker]

Comment on attachment 136184 [details]
Patch with unit test

R=me.

[Shawn Singh]

Comment on attachment 136184 [details]
Patch with unit test


Thanks!

[WebKit Review Bot]

Comment on attachment 136184 [details]
Patch with unit test

Clearing flags on attachment: 136184

Committed r113606: <http://trac.webkit.org/changeset/113606>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.