TextureMapper: nesting 3D rendering context support

[Fujii Hironori]

Created attachment 460275 [details]
test case

TextureMapperGL: rendering glitch of a 3d transformed text in Strange-Loop-2012

hyper texts in the slides aren't painted as expected if they are :hover.
https://github.com/BrendanEich/Strange-Loop-2012

[Fujii Hironori]

Safari, Chrome, Firefox: Very smooth animation
WebKitGTK, WinCairo WK1: not smooth animation
WinCairo WK2: not smooth animation, text disappears

[Fujii Hironori]

Disabling tet depth test makes the animation smooth. This seems to be a regression of my change (231816@main) enabling depth test.

diff --git a/Source/WebCore/platform/graphics/texmap/TextureMapperGL.cpp b/Source/WebCore/platform/graphics/texmap/TextureMapperGL.cpp
index f4d99408ff15..3890e1fa8c82 100644
--- a/Source/WebCore/platform/graphics/texmap/TextureMapperGL.cpp
+++ b/Source/WebCore/platform/graphics/texmap/TextureMapperGL.cpp
@@ -1043,7 +1043,6 @@ IntRect TextureMapperGL::clipBounds()
 
 void TextureMapperGL::beginPreserves3D()
 {
-    glEnable(GL_DEPTH_TEST);
     glClear(GL_DEPTH_BUFFER_BIT);
 }

[Fujii Hironori]

In this test case, <section> and <span> elements has transform-style:preseve-3d, but intermediate <a> element doesn't have it.
This is the case not supported as 231816@main change log explains.

<section> transform-style:preseve-3d
 +<a>
   +<span> transform-style:preseve-3d
     +<span::after>

[Radar WebKit Bug Importer]

<rdar://problem/95804784>

[Fujii Hironori]

Created attachment 463018 [details]
WIP patch

[Matt Woodrow]

In https://github.com/WebKit/WebKit/pull/6770 I'm adding 3 new TestExpectation annotations for this bug, for 3d tests that now pass on Mac/iOS, but still fail on GTK due to this bug (I think!).