Bug 257200

Summary:	Ignore bidi control characters while collecting fallback fonts
Product:	WebKit	Reporter:	Amanda Falke <abstractmachines>
Component:	Text	Assignee:	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>