2015400 - Fix the antialiasing of quad primitives

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P3)

Description

[Nicolas Silva [:nical]]

The Quad AA code has a few bugs:

• The batching code sets the wrong flag for some of the AA segments
• The shader incorrectly computes the position of the AA SDF by picking the loal rect after offsetting the sides. This causes the center part to always have AA applied to all of its side. This bug partially papers over the previous one and prevents AA from being applied to a subset of edges of a primitive.
• The AA segmentation has cracks sometimes (including multiple reftests). I don't know for sure if it is caused by the T-junctions in the segmentation or if it is an artifact of the previous described issues.
• The current segmentation only works if all segments are anti-aliased because the corners are covered by the left and right parts. If the top or bottom edge is not anti-aliased, then the side AA segments extend too far up/down.

Comment 1

[Nicolas Silva [:nical]]

Attachment: Bug 2015400 - Fix incorrect parameters in quad AA segments. r=gw

Comment 2

[Nicolas Silva [:nical]]

Attachment: Bug 2015400 - Only anti-alias the selected edges in the quad shader. r=gw

Comment 3

[Nicolas Silva [:nical]]

Attachment: Bug 2015400 - Wire up edge flags properly for quad primitives. r=gw

We used to be able to select which edges get anti-aliased for linear gradient primitives. That got lost in the transition to quads and is needed for all other patterns.
This patch adds plumbing for specifying which edges to antialias with two possible configurations: with or without an axis-aligned transform. CSS primitives don't anti-alias axis-aligned primitives, but SVG primitives should (alas they currently don't).

I suspect that with upocming changes to snapping we may end up representing this distinction some other way, but with this patch, the code internally at least reflects the options that we need to eventually support correctly.

For now the most pressing concern is that primitives need to be able to not anti-alias certain edges to avoid seams within items that are segmented inot multiple primitives. This is already the case of linear and radial gradients in some situations, and will probably be needed for the segmentation of border nine-patches.

Comment 4

[Nicolas Silva [:nical]]

Attachment: Bug 2015400 - Properly extrude AA segments when a subset of edges are anti-aliased. r=gw

Comment 5

[Nicolas Silva [:nical]]

Attachment: Bug 2015400 - Add wrench reftests for the interaction between AA and primitive segmentation. r=gw

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/82344af2f6e7
https://hg.mozilla.org/integration/autoland/rev/c9bc9d58e519
Fix incorrect parameters in quad AA segments. r=gw
https://github.com/mozilla-firefox/firefox/commit/e9b9bf6c88fc
https://hg.mozilla.org/integration/autoland/rev/755daf79f573
Only anti-alias the selected edges in the quad shader. r=gw
https://github.com/mozilla-firefox/firefox/commit/790b9d62a293
https://hg.mozilla.org/integration/autoland/rev/17c7347a64e4
Wire up edge flags properly for quad primitives. r=gw
https://github.com/mozilla-firefox/firefox/commit/cc6c02860896
https://hg.mozilla.org/integration/autoland/rev/f7e663d3d570
Properly extrude AA segments when a subset of edges are anti-aliased. r=gw
https://github.com/mozilla-firefox/firefox/commit/3b57528ee13f
https://hg.mozilla.org/integration/autoland/rev/37c8f604eb1b
Add wrench reftests for the interaction between AA and primitive segmentation. r=gw

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/3b2ddefac962
https://hg.mozilla.org/integration/autoland/rev/d9a74a466e96
Fix incorrect parameters in quad AA segments. r=gw
https://github.com/mozilla-firefox/firefox/commit/4a212357dcb1
https://hg.mozilla.org/integration/autoland/rev/89a362ffeabb
Only anti-alias the selected edges in the quad shader. r=gw
https://github.com/mozilla-firefox/firefox/commit/ac68be9588cd
https://hg.mozilla.org/integration/autoland/rev/b35c05e2f7a9
Wire up edge flags properly for quad primitives. r=gw
https://github.com/mozilla-firefox/firefox/commit/7fc68771222f
https://hg.mozilla.org/integration/autoland/rev/2942b1227c30
Properly extrude AA segments when a subset of edges are anti-aliased. r=gw
https://github.com/mozilla-firefox/firefox/commit/79fc088e22ff
https://hg.mozilla.org/integration/autoland/rev/bc2471db6d85
Add wrench reftests for the interaction between AA and primitive segmentation. r=gw

Comment 8

[amarc]

https://hg.mozilla.org/mozilla-central/rev/c9bc9d58e519
https://hg.mozilla.org/mozilla-central/rev/755daf79f573
https://hg.mozilla.org/mozilla-central/rev/17c7347a64e4
https://hg.mozilla.org/mozilla-central/rev/f7e663d3d570
https://hg.mozilla.org/mozilla-central/rev/37c8f604eb1b

Comment 9

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/d9a74a466e96
https://hg.mozilla.org/mozilla-central/rev/89a362ffeabb
https://hg.mozilla.org/mozilla-central/rev/b35c05e2f7a9
https://hg.mozilla.org/mozilla-central/rev/2942b1227c30
https://hg.mozilla.org/mozilla-central/rev/bc2471db6d85