1419863 - Slow depth clear shader by Angle

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, enhancement, P2)

Description

[Dzmitry Malyshau [:kvark]]

A RenderDoc capture shows a weird full-screen clear pass that doesn't belong to WR. It renders to depth only and the shader looks like this:

  Shader hash e8f66976-ac5a2d98-998c6426-787bd9e5
  ps_4_0
        dcl_constantbuffer cb0[2], immediateIndexed
        dcl_output oDepth
     0: mov oDepth, zValue_Depth.x
     1: ret

It takes considerable GPU time, according to RenderDoc measurements. The fact that it's just writing the depth in the fragment shader is terrible and inefficient. We should figure out who (I suspect Angle, reflected in the subject) and why issues this sort of clear.

Comment 1

[Dzmitry Malyshau [:kvark]]

Attachment: firefox_2017.11.22_12.49.23_frame360.rdc

Comment 2

[Dzmitry Malyshau [:kvark]]

Workaround in flight: https://github.com/servo/webrender/pull/2126