Webrender: Incorrect box-shadow rendering with large border radii and negative spread radius

[mstange]

http://tests.themasta.com/box-shadow-playground/#blue_red_outset_64_77_200_200_140x140_60x60_60x60_140x140_275_81_3_-46

[glennw]

I tested this with latest nightly and it appears to be visually correct. It's possible this was fixed with the change to render box shadows as clip sources recently. @mstange could you confirm?

[Darkspirit]

Fix range: https://github.com/servo/webrender/compare/0da6c839b3a0e165f1115fb9fe286be7540c24ed...f3af2632723f62eb7973a87bfaece43a675cefb5
Fixed by #2487.

[Darkspirit]

I am sorry. I found something. :-/
Nightly 61 x64 20180314102135 de_DE @ Debian Testing (KDE, Radeon RX480, 2560x1440)

(Still reproducible with WR @ 50c0cad255092f48784d9a142ea2069b121e7c13.)

[glennw]

Hmm, this probably just needs an extra condition to skip the minimal rect computation if the corner radii overlap, or something like that.

[glennw]

@Darkspirit Could you describe how to reproduce that issue above?

[Darkspirit]

1a) Opening the test case with Nightly (fresh profile with gfx.webrender.all;true).
1b) Opening it with the latest wr-future-update try build: mozregression --repo try --launch 71bad4a9edb6ebe30ae86a3b70e563eebc5f9510 --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://tests.themasta.com/box-shadow-playground/#blue_red_outset_64_77_200_200_140x140_60x60_60x60_140x140_275_81_3_-46"

1. Zooming out to 90%, 80% and less. (Ctrl -)

[glennw]

Ah, interesting - that's what I had tried but was not able to see the bug. When I adjusted the layout.css.devPixelsPerPx setting to 1.0 I am now able to see the bug. Thanks!