1914673 - WebRender update/scissor rects sometimes exceed the valid rects.

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P3)

Description

[Brad Werth [:bradwerth] | Out until Feb 2025]

As evidenced by the release assert in Bug 1817691, WebRender sometimes sends an update rect that is outside the bounds of a layer's valid rect. Logging indicates that these update rects are one pixel too large, indicating there's a rounding error somewhere in WR. WR attempts to ensure this in take_context, but clamps rects before transforming and rounding them, potentially leading this problem.

This is probably harmless, but platforms like the macOS layer manager might try to do optimization based on the assumption that the update rect is contained within the valid rect.

Comment 1

[Brad Werth [:bradwerth] | Out until Feb 2025]

Attachment: Bug 1914673: Ensure WebRender provides update rects within the bounds of valid rects.

This is an extra-double-sure clipping of the scissor rect to the valid
rect. This shouldn't matter since the dirty rect is clipped before the
creation of either of the other two rects, but will ensure that rounding
issues from the application of the transform in get_surface_rect won't
leave us with an out-of-bounds scissor rect.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1ca516749b37
Ensure WebRender provides update rects within the bounds of valid rects. r=gw

Comment 3

[pstanciu]

https://hg.mozilla.org/mozilla-central/rev/1ca516749b37