1682341 - Borders sometimes drawn incorrectly on Mali-T

Status: RESOLVED WORKSFORME

(Core :: Graphics: WebRender, defect)

Description

[Jamie Nicol [:jnicol]]

Attachment: malit-border.jpg

Testing on a Samsung Galaxy A5 (2017) - Mali-T830

It looks like some of the time the border segments aren't rendered in to the texture cache correctly. Sometimes nothing is shown, and sometimes some unrelated texture data is shown (as in the attached screenshot).

Reloading/zooming around on reddit.com reproduces fairly easily.

Comment 1

[Jamie Nicol [:jnicol]]

Zooming on https://www.w3schools.com/css/css_border.asp is a really good website for reproducing this.

However, since this push (some of bug 1679751) it no longer reproduces.

Prior to those commits, It seems to be that the bug occurs when a glyph is uploaded to the texture cache at the same time as we try to render a border in to the cache. One of those commits makes it so that glyphs are not ever allocated in to the same texture as borders, so we no longer hit this problem.

My suspicion was that the problem could theoretically still occur, for example if an image was uploaded at the same time as a border was rendered. However, I have been unable to reproduce this even when playing around with the code to ensure images are reuploaded every frame.

My plan is therefore to do nothing for now, and wait and see if the issue does pop up again. If it does, I had managed to figure out that using the prefers_batched_uploads texture upload path (where we upload to an intermediate texture then blit to the texture cache) avoids the problem. It may even be the case that we decide to enable that path for performance reasons on Mali-T anyway.

Comment 2

[Jamie Nicol [:jnicol]]

Haven't seen this in weeks despite using a previously affected device as my main phone for dogfooding. Closing as works for me.