1665274 - rasterflood_gradient spends a lot of time in brush_opacity

Status: RESOLVED FIXED

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

Description

[Lee Salzman [:lsalzman]]

When testing under SWGL, it seems that half the time in rasterflood_gradient is spent inside brush_opacity, aside from brush_radial_gradient comprising the other half, as rasterflood_gradient sets opacity on the background.

Glenn suggests that brush_opacity is probably very inefficient for this common case that is both axis-aligned and requires no edge AA. He suggests that we could possibly just use a hardware blend mode and a simple blit shader instead to fast-path that case. That would be a win for both SWGL and HW.

Comment 1

[Nicolas Silva [:nical]]

Attachment: Bug 1665274 - Speed up brush_opacity. r=lsalzman

• Remove a bunch of unnecessary arithmetic that un-premultiply/premultiply unmodified rgb channels.
• Clamp the uvs as we do in other shaders instead of doing a point-in-rect test.
• Add a shader variant that doesn't deal with anti-aliasing for the common axis-aligned transform case.

In the future we can merge the opacity funcionality into the brush_image shader to reduce the number of shaders.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/59d9ce47882b
Speed up brush_opacity. r=lsalzman

Comment 3

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/59d9ce47882b