Bug 228536 – [Win][Uniscribe] Remove the code rounding off glyph advances and offsets for non system fonts

• Status: RESOLVED
• Resolution: FIXED
• Component: Text

[Fujii Hironori]

[Win][Uniscribe] Remove the code rounding off glyph advances and offsets for system fonts

ComplexTextController::collectComplexTextRunsForCharacters has the following code.

> // Match AppKit's rules for the integer vs. non-integer rendering modes.
> if (!font->platformData().isSystemFont()) {
>     advance = roundf(advance);
>     offsetX = roundf(offsetX);
>     offsetY = roundf(offsetY);
> }

This was added by r18359.

See also: Bug#228363 Comment#2

[Fujii Hironori]

(In reply to Fujii Hironori from comment #0)
> This was added by r18359.

No. This code was added by r23462.

[Fujii Hironori]

(In reply to Fujii Hironori from comment #1)
> No. This code was added by r23462.

More precisely r23199 and r23154.

[Fujii Hironori]

Created attachment 434405 [details]
WIP patch

[Fujii Hironori]

In WinCairo, this patch makes the following ref tests fail.

  fast/text/emoji-gender-3.html [ ImageOnlyFailure ]
  fast/text/emoji-gender-4.html [ ImageOnlyFailure ]
  fast/text/emoji-gender-5.html [ ImageOnlyFailure ]
  fast/text/emoji-gender-6.html [ ImageOnlyFailure ]
  fast/text/emoji-gender-8.html [ ImageOnlyFailure ]

This is caused by the difference of how to get glyph advance between simple text code path and complex text code path.
The simple text code path is using cairo_scaled_font_glyph_extents, the complex text code path is using Uniscribe to get the glyph advance.

I think the simple text code path also should use Uniscribe.

However, the argument of Font::platformWidthForGlyph is Glyph not UChar.
Uniscribe (ScriptShape) takes a string, not glyphs.

Another approach is implementing Font::applyTransforms with Uniscribe (Bug 228363).
However, Font::applyTransforms is not applied to a single character.
This approach needs some modification to WidthIterator.

[Fujii Hironori]

I confirmed WinCairo doesn't have the comment#4 problem if it always uses the complex text code path.
In the complex text code path, it consistently uses Uniscribe.

[Fujii Hironori]

Created attachment 434495 [details]
WIP patch

The WinCairo problem is fixed by reimplementing Font::platformWidthForGlyph with GetCharABCWidthsI.

[Radar WebKit Bug Importer]

<rdar://problem/81500144>

[Fujii Hironori]

*** Bug 275674 has been marked as a duplicate of this bug. ***

[Fujii Hironori]

Pull request: https://github.com/WebKit/WebKit/pull/29992

[EWS]

Committed 280214@main (7ec79836337c): <https://commits.webkit.org/280214@main>

Reviewed commits have been landed. Closing PR #29992 and removing active labels.