Bug 235937 – [LFC][IFC] Using Fontcascade::spaceWidth to subtract the trailing space width may result in incorrect layout

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[zalan]

when the primary font does not have space glyph.

[zalan]

<rdar://88059633>

[zalan]

Created attachment 450492 [details]
Patch

[zalan]

Created attachment 450529 [details]
Patch

[zalan]

Created attachment 450538 [details]
Patch

[Maciej Stachowiak]

<rdar://88059633>

[zalan]

Created attachment 450559 [details]
Patch

[EWS]

Committed r288914 (246654@main): <https://commits.webkit.org/246654@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 450559 [details].

[WebKit Commit Bot]

Re-opened since this is blocked by bug 235998

[zalan]

Created attachment 450605 [details]
Patch

[zalan]

null terminator? where we're going we don't need null terminator.

[EWS]

Committed r288944 (246674@main): <https://commits.webkit.org/246674@main>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 450605 [details].

[Myles C. Maxfield]

Comment on attachment 450605 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=450605&action=review

> Source/WebCore/layout/formattingContexts/inline/text/TextUtil.cpp:94
> +    return fontCascade.width(TextRun { String { &space, 1 } });

There are no performance problems with this?

[zalan]

(In reply to Myles C. Maxfield from comment #12)
> Comment on attachment 450605 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=450605&action=review
> 
> > Source/WebCore/layout/formattingContexts/inline/text/TextUtil.cpp:94
> > +    return fontCascade.width(TextRun { String { &space, 1 } });
> 
> There are no performance problems with this?
I had run our classic PerformanceTests/Layout/line-layout-simple.html microbenchmark locally before landing this and it showed about 0.5% regression.
I also tested it with a slightly different version of the patch:
  const auto& spaceGlyphData = fontCascade.glyphDataForCharacter(space, false);
  return (!spaceGlyphData.font ? fontCascade.spaceWidth() : spaceGlyphData.font>widthForGlyph(spaceGlyphData.glyph)) + fontCascade.letterSpacing();
and it came back with the same numbers.