1494453 - Incorrect box shadow on header element on payun-payun parallax page

Status: RESOLVED FIXED

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

Description

[Kartikaya Gupta (email:[e-mail])]

Attachment: payunpayun.png

The box-shadow around the "payun-payun" header element on https://belen-albeza.github.io/scroll-demos/parallax.html isn't rendered properly. See attachment (from macOS, where it's squished into the top-left). On Windows the box shadow seems missing entirely.

Comment 1

[Emilio Cobos Álvarez (:emilio)]

Given the nested transforms it's likely a regression from https://github.com/servo/webrender/pull/3030 or such. I could take a look if nobody's looking at related issues.

Comment 2

[Emilio Cobos Álvarez (:emilio)]

Attachment: yaml test-case

Comment 3

[Emilio Cobos Álvarez (:emilio)]

Attachment: Simpler yaml test-case.

Expected: Green rounded rect over red rect of the same size.

Actual: Scaled green rounded rect.

Forcing each picture to have a surface fixes the position of the green primitive but not of the rounded clip, so I found one of the bogus space conversions but there's more...

Comment 4

[Emilio Cobos Álvarez (:emilio)]

So, some notes for myself while I debug this and try to wrap my head around all the coordinate spaces that are at play.

In the simplified test-case, all the primitives have the correct dimensions, we're just clipping out extra stuff incorrectly.

The render task for the clip mask has the right size and such, and as far as I can tell the uv computation to actually do the clipping in the brush shader is performed in device space so it looks correct to me as well (as in, the bounds for the rounded rect are also right, 100x100 device pixel).

The task origin also looks right to me, so my next guess is the clip mask getting incorrectly transformed in the shader, which produces a smaller unclipped area than what it should.

Comment 5

[Emilio Cobos Álvarez (:emilio)]

Attachment: GitHub Pull Request

Comment 6

[Darkspirit]

Attachment: 2018-10-05_12-52-20.mp4

left: non-WR, right: WR
At 100% zoom the left and right corners are cut-off. It depends on the zoom level.
At 30% zoom the shadow looks crazy, but this page has in general strange bugs, also with non-WR.

Comment 7

[Jeff Muizelaar [:jrmuizel]]

Emilio are you still looking at this?

Comment 8

[Emilio Cobos Álvarez (:emilio)]

This was fixed by that WR PR, but looks like it has regressed recently again... The page over-all has regressed quite a lot recently. I'll file and take a different bug for that.