1968618 - [meta] WebRender dithering support

Status: NEW

(Core :: Graphics: WebRender, task)

Description

[Sotaro Ikeda [:sotaro]]

WebRender dithering was disabled by the following

https://github.com/servo/webrender/pull/1042

---

There are a number of WPT/CSS tests that break with the current
gradient dither code. For now, disable dither on gradients so that
we can land a WR update in Servo. We can re-enable the dither
once the reftest bug is fixed.

Comment 1

[Sotaro Ikeda [:sotaro]]

Chromium tries to enable dither by calling PaintFlags::() or SkPaint::setDither().

They are called in the followings

• [1] RasterBufferProvider::PlaybackToMemory()
  • Dither is set only when format is SinglePlaneFormat::kRGBA_4444)
• [2]DecodingImageGenerator::GetPixels()
  • Dither is set only when it is necessary.
• [3]Gradient::ApplyToFlags()
  • gradients are always dithered.

[1] and [2] seems not related to WebRender. Only [3] seems necessary for WebRender.

3 Types of gradients are created related to [3] by the followings.

• Gradient::CreateLinear()
• Gradient::CreateRadial()
• Gradient::CreateConic()

And Skia could disable dither with the following checks

• SkPaintPriv::ShouldDither()
• should_dither()

Comment 2

[Sotaro Ikeda [:sotaro]]

WebRender has dither implementation, though it is disabled. It was originally added by https://github.com/servo/webrender/pull/1042.

Then it was refactored by Bug 1688323.

Radial and conic gradients were added by Bug 1687977.

WebRenderOptions::enable_dithering seems care only for linear gradient for now.

• https://searchfox.org/mozilla-central/rev/06e32c3ea654f5a74e08cc1040b52a3646d639a7/gfx/wr/webrender/src/renderer/shade.rs#729

Comment 3

[Sotaro Ikeda [:sotaro]]

Test failure seems not happen by enabling dither only with hardware WebRender.
https://treeherder.mozilla.org/jobs?repo=try&revision=410ed038a6c6f9d2a1a529afb71899f48526a60f

Comment 4

[Sotaro Ikeda [:sotaro]]

(In reply to Sotaro Ikeda [:sotaro] from comment #3)

Test failure seems not happen by enabling dither only with hardware WebRender.
https://treeherder.mozilla.org/jobs?repo=try&revision=410ed038a6c6f9d2a1a529afb71899f48526a60f

It was Bug 1974916.

Comment 5

[Sotaro Ikeda [:sotaro]]

Current test failure status.

https://treeherder.mozilla.org/jobs?repo=try&revision=574057a7a59d93c8a47b1cf62a20321179803352