commit 6763eaa83051f7d02aed7f27d578339f532b8cd5
author Delan Azabani <dazabani@igalia.com> Thu Aug 26 11:44:24 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Aug 26 11:44:24 2021
tree 01460b13a0f058fdbabc131f89c53dad6ca2c364
parent 108cf1b27385c6d25f45f6526f89a9ae8ea88f23

CSS highlight painting: split originating and ::selection decorations

This patch builds on /c/2902289 by splitting the paints for unselected
and selection text, which means that for the first time, all of these
properties should hold true regardless of whether text is selected:

P1. underlines and overlines are never painted over text
P2. lines-through are always painted over text
P3. decorations on any unselected parts are in originating td-color
P4. selected part decorations paint over ::selection background
P5. ::selection background always paints over unselected text

Here’s a comparison of how these properties have evolved:

• pre-M90 ensured P1 + P4, but violated P2 + P3 + P5
• /c/2647046 ensured P1 + P5, but violated P2 + P3 + P4
• /c/2902289 ensured P2 + P4 + P5, but violated P1 + P3
• this patch ensures P1 + P2 + P3 + P4 + P5

To test the properties more effectively, I’ve replaced one of my
highlight painting tests with two more effective tests, and added
smaller tests for properties P1 through P4.

<https://wpt.live/css/css-pseudo/highlight-painting-003.html> now
tests solid decorations with ::selection underline and originating
line-through, plus an originating background.

• https://bucket.daz.cat/ee288ed9a20b1a2f.png = pre-M90
• https://bucket.daz.cat/e689c7ada0c05594.png = /c/2647046
• https://bucket.daz.cat/42d48433dfc51e15.png = /c/2902289
• https://bucket.daz.cat/1658767a17294d93.png = this patch

<https://wpt.live/css/css-pseudo/highlight-painting-004.html> tests
wavy decorations, but with originating underline and ::selection
line-through, and no originating background:

• https://bucket.daz.cat/5e28cd46a5972359.png = pre-M90
• https://bucket.daz.cat/b44c05422d47a0b3.png = /c/2647046
• https://bucket.daz.cat/5e28cd46a5972359.png = /c/2902289
• https://bucket.daz.cat/6647e4443a92cec5.png = this patch

For reference, here are the refs:

• https://bucket.daz.cat/439df4145d54fede.png = 003-ref
• https://bucket.daz.cat/05b20f2ec3675e7e.png = 004-ref1
• https://bucket.daz.cat/c898a37e256b3e44.png = 004-ref2
• https://bucket.daz.cat/bd4b272d1bcdf932.png = 004-ref3

This brings us closer to passing those tests, but not quite there.
Next up, we need to recolor the decorations lifted from originating
style to the ::selection overlay to ::selection’s color, not its
text-decoration-color as done in <https://crrev.com/c/2383212>.

Bug: 1147859
Change-Id: I011323db9b481175fb750ab810b6741239522087
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2903387
Commit-Queue: Delan Azabani <dazabani@igalia.com>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#915543}