[Webkit-unassigned] [Bug 236307] New: Replacing space with GSUB code produces wrong rendering

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=236307

            Bug ID: 236307
           Summary: Replacing space with GSUB code produces wrong
                    rendering
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: akiem at underware.nl
                CC: mmaxfield at apple.com

Created attachment 451260

  --> https://bugs.webkit.org/attachment.cgi?id=451260&action=review

Test files to reproduce the described bug

1. replacing space with GSUB code produces wrong rendering
The reason for this is the following (explained by Myles Maxfield):
This is due to our “charactersTreatedAsSpace” logic. We measure text in differently-sized chunks different places in WebKit, and we want to maintain the invariant that, even if we split up the text and measure word-by-word, that will get the same results as if you measured the whole string including spaces. To do this, we have code in WebKit where we clobber the widths of space glyphs after shaping to set them to be equal to what they were before shaping. Fixing this would be a large architectural change; it’s something I’d like to do eventually, though.

For test files please check the attachment.

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