1012797 - Speed up rendering of linear gradients when only painting the uniform color beyond the gradient edge

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Markus Stange [:mstange]]

Attachment: v1

Bugzilla uses a linear-gradient(#D7D3C8, #F6F4EC 400px) as its background. This gradient is only an actual gradient in the top 400px of the page; below that it's just a uniform color. If our paint area is completely in the uniform color area we can just use a simple color fill when painting.

This also works around bug 1010188, which is a pixman (and gdi?) problem on very long bugzilla pages, i.e. longer than 32768px: When scrolled down far enough, the ctx->Translate(tileRect.TopLeft()) call translates by a value larger than 2^15, and pixman's internal matrix storage apparently uses 16.16 fixed point, so we fail to render the gradient. This patch is a workaround for that particular bugzilla use case.

The math in this patch is your work, roc. (from bug 508730)

Comment 1

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

Comment on attachment 8424990 [details] [diff] [review]
v1

Review of attachment 8424990 [details] [diff] [review]:
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Nice! That Bugzilla bug has been bugging me :-)

Comment 2

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

Might want to add a reftest for the Bugzilla rendering bug too.

Comment 3

[Markus Stange [:mstange]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/5574008af2b6

I'll add tests for giant gradients when I fix the general case in bug 1011166.

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/5574008af2b6