OS: Arch Linux
Graphics Hardware: AMD Radeon HD 4850 (RV770)

The control elements shown as overlay on Twitter videos are blurry, see the attached screenshot (ignore the strange looking video itself, this is bug 1536878). Fullscreen videos are not affected.

This is a regression, with mozregression I found:

Last good revision: 0fedcd9cdd51f06c9e177a1b81c04c7ac93e27bf
First bad revision: d0221689e8e9a720dca3bdc7f4c3371c09f6626c

Pushlog:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=0fedcd9cdd51f06c9e177a1b81c04c7ac93e27bf&tochange=d0221689e8e9a720dca3bdc7f4c3371c09f6626c

This points to bug 1539048.

I can only test on Linux here, so I don't know if other operating systems are affected. Bug 1526756 was about the same issue, but it was fixed before the regression occured.

sharp control elemens for comparison

This seems to be fixed by my current snapping investigations, where the primitive rect / visible rect calculations for pictures on the CPU side often need to account for snapping, otherwise there is some slight distortion.

The issue is also present on Windows 10 -- Firefox Nightly 68.0a1 (20190419094745)

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=8a50006bd97af5443bf151a4ddac00621a18b6f3

We currently calculate a picture's local rect when we are doing the
first picture traversal. It was composed of the union of the clipped
local rects of its children. However the true local rect of a picture is
the union of the snapped clipped local rects of its children. The
snapping is done in device space, but we won't know the exact transform
until we establish the raster roots, which is based on the picture's
local rect.

As such, we create an estimated local rect which is how we currently
calculate the local rect. Then once the raster roots have been selected,
we recalculate the local rect of the picture based on its children
during update visibility.

This patch should have not contain any functional changes.

We currently do most snapping on the GPU in the shader. However the
picture's local rect needs to take into account the snapping done there,
so we need to calculate this earlier in the pipeline. Instead of using
the clipped primitive local rects to create the picture's own local
rect, we now snap the child local rects first. If no snapping is
required, there should be no functional change. If snapping is required,
there should be fewer visual distortions caused by an inaccurate picture
local rect.

Historically we calculated the snapping offsets in the GPU shaders.
Because this information is always needed on the CPU side, we now just
pass the values into the shader instead of recalculating again. This
ensures we will use the same set of values consistently and makes it
easier to adjust how we snap in the future.

This patch should have no functional change on the output of WebRender
itself.

This change didn't end up being everything I wanted it to be. In particular I had trouble moving from snapping to the visible rect, to snapping to the primitive rect as originally intended. This means there are still outstanding snapping issues (e.g. reddit logo) that I had hoped this would fix. This is arguably better however on its own and I don't want to hold up on fixing everything in one go... we will probably have to settle for incremental wins to meet release timelines ;).

Updated tries:

try (reftests): https://treeherder.mozilla.org/#/jobs?repo=try&revision=3a784cf5769aae42b03a97924d7f9372a71a1156
try (talos): https://treeherder.mozilla.org/#/jobs?repo=try&revision=c2ef6f3bc9346cc05dcdd8f736e9bc8335312309

Does not appear to be any significant talos changes.

Backed out 3 changesets (Bug 1540200) for reftest failure at: build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html

Push with failure: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&resultStatus=testfailed%2Cbusted%2Cexception&classifiedState=unclassified&selectedJob=243729562&revision=0259eb7967f41e2476320a899efa85e59a3fe837

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=243767926&repo=mozilla-inbound&lineNumber=82621

Backout link: https://treeherder.mozilla.org/#/jobs?repo=mozilla-inbound&resultStatus=testfailed%2Cbusted%2Cexception&classifiedState=unclassified&selectedJob=243729562&revision=f816de04249b85cfb7a83ce06167984b93f96a4a

23:21:39     INFO - REFTEST TEST-START | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html
23:21:39     INFO - REFTEST TEST-LOAD | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html | 21 / 94 (22%)
23:21:39     INFO - ++DOMWINDOW == 42 (0x11ffaa000) [pid = 1464] [serial = 52] [outer = 0x11ff3d020]
23:21:39     INFO - REFTEST TEST-UNEXPECTED-FAIL | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html | image comparison, max difference: 51, number of differing pixels: 272
23:21:39     INFO - REFTEST   IMAGE 1 (TEST): 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23:21:39     INFO - REFTEST   IMAGE 2 (REFERENCE): data:image/png;base64,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23:21:39     INFO - REFTEST INFO | Saved log: START file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html
23:21:39     INFO - REFTEST INFO | Saved log: [CONTENT] OnDocumentLoad triggering AfterOnLoadScripts
23:21:39     INFO - REFTEST INFO | Saved log: Initializing canvas snapshot
23:21:39     INFO - REFTEST INFO | Saved log: DoDrawWindow 0,0,800,1000
23:21:39     INFO - REFTEST INFO | Saved log: [CONTENT] RecordResult fired
23:21:39     INFO - REFTEST INFO | Saved log: RecordResult fired
23:21:39     INFO - REFTEST INFO | Saved log: RecordResult fired
23:21:39     INFO - REFTEST TEST-END | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3e.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html
23:21:39     INFO - ++DOMWINDOW == 43 (0x117e8c800) [pid = 1464] [serial = 53] [outer = 0x11ff3d020]
23:21:39     INFO - REFTEST TEST-START | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3f.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html
23:21:39     INFO - REFTEST TEST-LOAD | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3f.html | 22 / 94 (23%)
23:21:39     INFO - ++DOMWINDOW == 44 (0x1190a9400) [pid = 1464] [serial = 54] [outer = 0x11ff3d020]
23:21:39     INFO - REFTEST INFO | REFTEST fuzzy test (0, 0) <= (0, 0) <= (1, 126)
23:21:39     INFO - REFTEST TEST-PASS | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3f.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html | image comparison, max difference: 0, number of differing pixels: 0
23:21:39     INFO - REFTEST TEST-END | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3f.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html
23:21:39     INFO - ++DOMWINDOW == 45 (0x1209d2c00) [pid = 1464] [serial = 55] [outer = 0x11ff3d020]
23:21:39     INFO - REFTEST TEST-START | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3g.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html
23:21:39     INFO - REFTEST TEST-LOAD | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3g.html | 23 / 94 (24%)
23:21:39     INFO - ++DOMWINDOW == 46 (0x1209d7400) [pid = 1464] [serial = 56] [outer = 0x11ff3d020]
23:21:39     INFO - REFTEST INFO | REFTEST fuzzy test (0, 0) <= (51, 272) <= (1, 126)
23:21:39     INFO - REFTEST TEST-UNEXPECTED-FAIL | file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3g.html == file:///Users/cltbld/tasks/task_1556664378/build/tests/reftest/tests/layout/reftests/w3c-css/submitted/masking/mask-image-3-ref.html | image comparison, max difference: 51, number of differing pixels: 272

try (after rebase): https://treeherder.mozilla.org/#/jobs?repo=try&revision=915ad6b2d4f431c0ade554e2c21ad2406d5f0133

This try shows the test passing.

try (more tests/platforms): https://treeherder.mozilla.org/#/jobs?repo=try&revision=cac29739e4656f864c0a07218e944f15b149bcd4

If the above try is green, I will try relanding.

Looks like it is clean, let's try landing again...

Backout for causing merge conflicts

Backout: https://hg.mozilla.org/mozilla-central/rev/647a90020b45dc8cdc45370bf3a91df815084b8c

Looks like some code got moved around, sigh. Let's try this one more time....

https://treeherder.mozilla.org/#/jobs?repo=try&revision=fb4db78ecb3bbce0eb98a7707cc0c60bbccc7856

Actually leave no stone unturned, run Windows/Mac WR reftests:

https://treeherder.mozilla.org/#/jobs?repo=try&revision=32e78e1e30a06d158763458fd65ee016002d3f3a

https://hg.mozilla.org/mozilla-central/rev/403ea69a03b0
https://hg.mozilla.org/mozilla-central/rev/eefb300b7640
https://hg.mozilla.org/mozilla-central/rev/34510ca46cc6