1243514 - Fix visibility computation in nsDisplayResolution

Status: RESOLVED INCOMPLETE

(Core :: Layout, defect)

Description

[Kartikaya Gupta (email:[e-mail])]

Full backstory is woven between bug 1225508 and bug 1228602, but the short version is that if there is some content with a resolution (i.e. has a nsDisplayResolution) but no displayport, then the visibility computation for it might be incorrect.

This idea was first surfaced in bug 1225508 as a possible cause, and was worked around by just setting a displayport for those cases. Follow-up work in bug 1228602 uncovered the real root cause for that particular bug in the tiling code. Theoretically this means that the patch from bug 1225508 could be backed out without regressing about:firefox. Theoretically though the scenario with resolution+no displayport is still a problem, and even if we don't encounter it on about:firefox we might encounter it elsewhere. So until the nsDisplayResolution code is fixed it's safer to leave the displayport applied.

:tnikkel has a WIP to make the nsDisplayResolution changes in attachment 8696718 [details] [diff] [review]. This should be dusted off, verified, and landed. And then we can back out the patch from bug 1225508 so that we no longer set a displayport in these cases, because nsDisplayResolution should do the right thing.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

This is obsoleted by recent changes and in particular https://bugzilla.mozilla.org/show_bug.cgi?id=1641246 will remove nsDisplayResolution entirely.