Bug 311246 – Ligatures affect layout for 0 font-size

• Component: New Bugs
• Status: RESOLVED FIXED

[Alex]

Here's an example of the issue:

1. I have an icon-only button.
2. I have text inside that button for accessibility tools.
3. I hide text visually using font-size: 0.
4. I use Google Manrope font that has ligatures, for this example, for double t – "tt"
5. The ligatures affect layout even though font size is 0, see the Codepen below:

https://codepen.io/waterplea/pen/OPRZyex

A button with "User" inside is displayed correctly, a button with "Settings" inside is off-center in Safari due to double t.

[Ahmad Saleem]

I am able to reproduce this bug on Safari Technology Preview 240, where in second button `gear` icon is not centered like first one and is bit shifted on left side. I am not able to reproduce this bug on Chrome Canary 148.0.7766.0 (Official Build) canary (arm64) .

[Radar WebKit Bug Importer]

<rdar://problem/173840866>

[Ahmad Saleem]

First bit in:

void ComplexTextController::collectComplexTextRuns()

We have the early return where if computedSize of font is `0`, we early return.

if (!m_end || !m_fontCascade->size())
        return;

So it might fallback to Simple Text Run.

[Ahmad Saleem]

We might be missing same guard in SimpleTextRun and need to skip this bit.

[Ahmad Saleem]

This fixes it:

Source/WebCore/platform/graphics/coretext/FontCoreText.cpp

Font::applyTransforms

if (!platformData().size())
        return makeGlyphBufferAdvance();

Before  auto handler = ^(CFRange range, CGGl

[Karl Dubost]

Created attachment 478873 [details]
wpt-testcase

Working locally with https://wpt.live/
To be removed before uploading with the patch.

[Ahmad Saleem]

Pull request: https://github.com/WebKit/WebKit/pull/61819

[EWS]

Committed 310394@main (36d29c6355ca): <https://commits.webkit.org/310394@main>

Reviewed commits have been landed. Closing PR #61819 and removing active labels.

[Ahmad Saleem]

Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/58928