Steps to reproduce: 1. Go to http://gifpaint.com/ and dismiss the message box. 2. Scroll down. 3. Scroll up. When scrolling up, the white canvas area in the middle briefly becomes light gray.

> mozregression --launch 2018-03-12 --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/" Debian Testing (KDE, Radeon RX480) Does not happen at 100% zoom and not on every zoom level. Sometimes it's just a light-grey flickering while scrolling, sometimes just like seen in this screencast.

> Sometimes it's just a light-grey flickering while scrolling, sometimes just like seen in this screencast. flickering: at 140% zoom, untouched window height static color change: with a smaller window height ------ at 140% zoom. mozregression --good 2018-01-15 --bad 2018-03-12 --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/" > 14:09.21 INFO: Last good revision: cfc5d19e856fc43766669069b7e2695dd519e5c3 > 14:09.21 INFO: First bad revision: 81f389c2524e58b4b95844667719cc1642573019 > 14:09.21 INFO: Pushlog: > https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=cfc5d19e856fc43766669069b7e2695dd519e5c3&tochange=81f389c2524e58b4b95844667719cc1642573019 > 81f389c2524e Kartikaya Gupta — Bug 1440664 - Update reftest annotation for changes in WR PR 2471. r=jrmuizel > 507a25c3afd0 Kartikaya Gupta — Bug 1440664 - Update reftest annotation for WR PR 2443. r=jrmuizel > 6098d2c015d7 Kartikaya Gupta — Bug 1440664 - Re-generate FFI header. r=jrmuizel > a5991299ebd0 Kartikaya Gupta — Bug 1440664 - Update Cargo lockfiles and re-vendor rust dependencies. r=jrmuizel > c066c419e378 Martin Robinson — Bug 1440664 - Update gecko WR bindings for API changes in WR PR 2449. r=kats > 6f54af02c2e6 Kartikaya Gupta — Bug 1440664 - Update webrender to commit 22b831c02479eea31821f49a0fac7dd699083557. r=jrmuizel try builds from bug 1440664: > WR @ 992dbd3f07b143f35581012082aa59fbda7c387e mozregression --repo try --launch 4916bd1bb3e9470ea106ebf45859b68b2a1b474c --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/" bad > WR @ 0b711f2e514107361deef4297c3c7da794d4835c mozregression --repo try --launch 9cbf4580d196e5997b2ca7f8ce4fa26b49e47b0f --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/" bad Regression range: https://github.com/servo/webrender/compare/8a19316a733a484bf9bafb8257e3008b1418bfe4...992dbd3f07b143f35581012082aa59fbda7c387e

Nical, this looks like you.

If this really is caused by the same bug as bug 1446129, then I suggest debugging the testcase in that bug instead of debugging gifpaint.com itself.

Fix in https://github.com/servo/webrender/pull/2568

try build from bug 1447998 comment 4: > WR @ 00b85801f8c09431e5963a9e1dcd1a9087b744b9 mozregression --repo try --launch 5f58a8fa82a9c7ed75867993058a03e3b2e58827 --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/|https://bug1446129.bmoattachments.org/attachment.cgi?id=8959296|http://localhost/background_broken.html" * bug 1445034: bad * bug 1446129: bad * bug 1446626: bad try build from bug 1447998 comment 5: > WR @ 43c0cde08f71b800d45ad35119bd20b561288a34 mozregression --repo try --launch a92e61fbb71b3b6e9825e5bb15e58fd9887fb40f --pref gfx.webrender.all:true startup.homepage_welcome_url:"http://gifpaint.com/|https://bug1446129.bmoattachments.org/attachment.cgi?id=8959296|http://localhost/background_broken.html" * bug 1445034: fixed * bug 1446129: fixed * bug 1446626: still bad

Looks like this was fixed in https://github.com/servo/webrender/pull/2568.