Bug 255298

Summary: Object replacement character (0xFFFC) generates null (0) glyph
Product: WebKit Reporter: Vitor Roriz <vitor.roriz>
Component: TextAssignee: Myles C. Maxfield <mmaxfield>
Status: RESOLVED FIXED    
Severity: Normal CC: gsnedders, mmaxfield, webkit-bug-importer
Priority: P2 Keywords: InRadar
Version: Other   
Hardware: Unspecified   
OS: Unspecified   

Description Vitor Roriz 2023-04-11 12:30:48 PDT 
We are getting an empty glyphData object (thus a null glyph (0)) when the input character is the object replacement character (0xFFFC).
If such input is decorated with text-emphasis-marker, this will cause the marker not to be painted after https://github.com/WebKit/WebKit/pull/12471 is merged.

This is because, the null glyph gets replaced by the deleted glyph (0xFFFF) and after the PR is merged, we no longer will draw markers for associated deleted glyphs.

How to reproduce it:


<p class="foo">X</p>

.foo {
  writing-mode:vertical-lr;
  text-combine-upright:all;
  text-emphasis:filled;
}
Comment 1 Radar WebKit Bug Importer 2023-04-11 12:31:01 PDT 
<rdar://problem/107897203>
Comment 2 Sam Sneddon [:gsnedders] 2023-05-05 12:32:56 PDT 
*** Bug 256372 has been marked as a duplicate of this bug. ***
Comment 3 Myles C. Maxfield 2023-05-22 14:56:34 PDT 
It's totally legit for characters to be mapped to the 0 glyph. The fact that the object replacement character gets mapped to the 0 glyph isn't a bug; it's expected.

If we recently added logic that says "the 0 glyph shouldn't get an emphasis mark" then that logic is wrong.
Comment 4 Myles C. Maxfield 2023-06-02 15:43:01 PDT 
Pull request: https://github.com/WebKit/WebKit/pull/14642
Comment 5 EWS 2023-06-05 20:02:13 PDT 
Committed 264886@main (aba48e65ac8b): <https://commits.webkit.org/264886@main>

Reviewed commits have been landed. Closing PR #14642 and removing active labels.