Bug 257200

Summary: Ignore bidi control characters while collecting fallback fonts
Product: WebKit Reporter: Amanda Falke <abstractmachines>
Component: TextAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Normal CC: mmaxfield, webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   

Description Amanda Falke 2023-05-23 07:41:19 PDT
https://drafts.csswg.org/css-text-3/#white-space-processing
"Unsupported Default_ignorable characters must be ignored for text rendering."

As mentioned in 245154@main, taking zero width glyphs (e.g. control characters) into consideration while collecting fallback font information
may result in incorrect line height and baseline positioning; an alternative mentioned in 245154@main was to check against unicode ranges to omit
certain glyphs.

246121@main fixed a regression in which bidi control chars rendered, and replaced our previous hardcoded list of Default_ignorable characters with the helper
function,FontCascade::isCharacterWhoseGlyphsShouldBeDeletedForTextRendering (also refactored in 260081@main). That helper function covers the use case 'rightToLeftOverride' which the test `LayoutTests/fast/text/fallback-font-and-zero-width-glyph.html`, currently marked as failing in glib, relies on.
Comment 1 Amanda Falke 2023-05-23 08:59:59 PDT
PR, WIP. https://github.com/WebKit/WebKit/pull/14240
Comment 2 EWS 2023-05-25 01:29:59 PDT
Committed 264509@main (07b1f5f81cef): <https://commits.webkit.org/264509@main>

Reviewed commits have been landed. Closing PR #14240 and removing active labels.
Comment 3 Radar WebKit Bug Importer 2023-05-25 01:30:18 PDT
<rdar://problem/109820978>