1669960 - Using glBlitFramebuffers to copy picture cache textures results in corruption on Mali-G72

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect)

Description

[Jamie Nicol [:jnicol]]

This is a regression from bug 1669494, which switched us to using glBlitFramebuffer rather than glCopyImageSubData to resize picture cache textures. As a result I'm now seeing blurry or corrupt text on my Samsung Galaxy S9.

That patch was in response to a performance issue spotted on Mali-T, but I applied the change to Mali-G too as a precaution. It seems like that was the wrong choice, so let's revert it on Mali-G. Thankfully on Mali-T I don't see any corruption.

Comment 1

[Jamie Nicol [:jnicol]]

Note that bug 1669567 should fix this anyway, because we will stop resizing (ie allocate new texture and blit old to new) picture cache textures.

But I think we want to fix this anyway so we don't get any surprises in the future if we start blitting textures again.

Comment 2

[Jamie Nicol [:jnicol]]

Attachment: malig-corruption.jpg

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

Set release status flags based on info from the regressing bug 1669494

Comment 4

[Jamie Nicol [:jnicol]]

Using GL_NEAREST instead of GL_LINEAR for the glBlitFramebuffer also appears to fix this. Maybe we should be using GL_NEARST anyway, since the source and dest textures are the same dimensions, and it might be faster. But that seems more brittle than just preferring glCopyImageSubData.

Comment 5

[Jamie Nicol [:jnicol]]

Attachment: Bug 1669960 - Revert to using glCopyImageSubData rather than glBlitFramebuffer on Mali-G r?gw

In bug 1669494 we switched Mali-T and Mali-G devices to use
glBlitFramebuffer rather than glCopyImageSubData when resizing
textures. This was in response to a performance issue noticed on
Mali-T, but Mali-G was switched too as a precaution.

However, Mali-G appears to have a buggy implementation of
glBlitFramebuffer, resulting in corruption. Luckily, Mali-T does not
appear to have such a problem, so we can keep Mali-T using
glBlitFramebuffer, but revert Mali-G to glCopyImageSubData.

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/859eba74bbab
Revert to using glCopyImageSubData rather than glBlitFramebuffer on Mali-G r=gw

Comment 7

[Cristina Coroiu [:ccoroiu]]

https://hg.mozilla.org/mozilla-central/rev/859eba74bbab

Comment 9

[Jamie Nicol [:jnicol]]

I was looking through the webrender driver issues wiki page and saw this, and remembered that the description was incorrect. The corruption was due to resizing the GPU cache rather than picture cache tiles. And that was due to GL_LINEAR not being supported for blitting RGBAF32 textures. (bug 1677757)