228861 - Opacity ignored when containing block is not visible

Status: RESOLVED FIXED

(Core :: Web Painting, defect, P1)

Description

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Ian found a bug where, if the containing block for a translucent element is not
in the repaint area, then the translucency is not applied.

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: testcase

Just scroll down until the gray-on-red text is offscreen. The fixed yellow DIV
will suddenly become opaque. It should remain translucent.

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

I don't see the bug in a quick look at the code. I'll look into it later.

Comment 3

[Henrik Skupin [:whimboo][⌚️UTC+1]]

As an additional comment to
http://bugzilla.mozilla.org/show_bug.cgi?id=212366#c80 i can see this slow
update when i scroll the page. It happens only when the yellow box is behind the
invisible one or what it is. At the bottom it's working fine. But this would
depend on bug 64401 i think.

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix

Simple fix. We need to stop AddToDisplayList from dropping CLIP and FILTER
instructions on the floor just because they have an empty intersection with the
damage rect. Later we're going to reparent content under them and that content
will be clipped by the CLIP and will expand the FILTER region.

Note that if there is no reparented content, then OptimizeDisplayListClipping
and OptimizeTranslucentRegions will later figure out that the PUSH/POP
CLIP/FILTER pairs have nothing inside them and will remove the useless
instructions.

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

checked in