Bug 114338 – Nested opacity with overflow may display wrong results when composited

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Noam Rosenthal]

New ref test added, compositing/overflow/overflow-scaled-descendant-overlapping.html, fails on Mac/WK2.

[Simon Fraser (smfr)]

compositing/overflow/overflow-scaled-descendant-overlapping.html doesn't have opacity. Did you mean something else?

[Noam Rosenthal]

(In reply to comment #1)
> compositing/overflow/overflow-scaled-descendant-overlapping.html doesn't have opacity. Did you mean something else?

Right, I meant LayoutTests/compositing/overlap-blending/nested-overlap-overflow.html.

[Simon Fraser (smfr)]

Ugh, who writes testcases with body > div > div > div. So hard to grok.

[Simon Fraser (smfr)]

I think this is clipping of positioned objects inside overlfow being incorrect when they are composited. It's not related to opacity.

[Noam Rosenthal]

(In reply to comment #4)
> I think this is clipping of positioned objects inside overlfow being incorrect when they are composited. It's not related to opacity.
At least for TextueMapper this only appeared when adding opacity, since this triggered a code path with intermediate surfaces (the equivalent of transparency layers in GraphicsContext).
Not sure if this happens on CA without transparency layers.

[Fujii Hironori]

This test isn't valid.

If an element has overflow:hidden and transform, it should clip positioned descendants.
nested-overlap-overflow.html has transform, but nested-overlap-overflow-expected.html.
Firefox, Chrome and Safari render same.

If I added 'transform' to nested-overlap-overflow-expected.html, Firefox and Chrome clip the green box like nested-overlap-overflow.html.

diff --git a/LayoutTests/compositing/overlap-blending/nested-overlap-overflow-expected.html b/LayoutTests/compositing/overlap-blending/nested-overlap-overflow-expected.html
index aaae129798aa..3430fedddac8 100644
--- a/LayoutTests/compositing/overlap-blending/nested-overlap-overflow-expected.html
+++ b/LayoutTests/compositing/overlap-blending/nested-overlap-overflow-expected.html
@@ -17,6 +17,7 @@
             body > div {
                 height: 100px;
                 overflow: hidden;
+                transform: translateX(0);
             }
             body > div > div {
                 width: 200px;


WebKit doesn't clip in that case. This is another bug tracked by bug#241641.

[Fujii Hironori]

Created attachment 460707 [details]
Patch

[EWS]

Committed 252184@main (e429d8971cc7): <https://commits.webkit.org/252184@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 460707 [details].

[Radar WebKit Bug Importer]

<rdar://problem/96533950>