Bug 32794 – With text-rendering: optimizelegibility, sometimes lines run too long

• Status: RESOLVED
• Resolution: FIXED
• Component: Text

The attached test case shows the using text-rendering: optimizelegibility can cause lines to break too late, and the effect that it has on left-aligned and on justified text. Perhaps there is a discrepancy between how text is measured for the purpose of line breaking and how it’s actually rendered afterwards.

Created attachment 45282 [details]
Test case

<rdar://problem/7488126>

Created attachment 46010 [details]
Allow trailing space to affect kerning when measuring a word

[WebKit Review Bot]

style-queue ran check-webkit-style on attachment 46010 [details] without any errors.

[Darin Adler]

Comment on attachment 46010 [details]
Allow trailing space to affect kerning when measuring a word

> +            TextRenderingMode textRenderingMode = f.fontDescription().textRenderingMode();
> +            // Non-zero only when kerning is enabled, in which case we measure words with their trailing
> +            // space, then subtract its width.
> +            int wordTrailingSpaceWidth = textRenderingMode == OptimizeLegibility || textRenderingMode == GeometricPrecision ? f.spaceWidth() + wordSpacing : 0;

I think it would be clearer to have a function named allowsKerning or something like that. It could contain:

    TextRenderingMode textRenderingMode = f.fontDescription().textRenderingMode();
    textRenderingMode == OptimizeLegibility || textRenderingMode == GeometricPrecision

Then you could saw:

    wordTrailingSpaceWidth = allowsKerning(f) ? f.spaceWidth() + wordSpacing : 0;

Maybe there's a better name than "allows kerning", though.

(In reply to comment #5)
> (From update of attachment 46010 [details])
> > +            TextRenderingMode textRenderingMode = f.fontDescription().textRenderingMode();
> > +            // Non-zero only when kerning is enabled, in which case we measure words with their trailing
> > +            // space, then subtract its width.
> > +            int wordTrailingSpaceWidth = textRenderingMode == OptimizeLegibility || textRenderingMode == GeometricPrecision ? f.spaceWidth() + wordSpacing : 0;
> 
> I think it would be clearer to have a function named allowsKerning or something
> like that. It could contain:
> 
>     TextRenderingMode textRenderingMode =
> f.fontDescription().textRenderingMode();
>     textRenderingMode == OptimizeLegibility || textRenderingMode ==
> GeometricPrecision
> 
> Then you could saw:
> 
>     wordTrailingSpaceWidth = allowsKerning(f) ? f.spaceWidth() + wordSpacing :
> 0;
> 
> Maybe there's a better name than "allows kerning", though.

I intend to add two Font methods (one for kerning and one for ligatures) and deploy them here and in the many other places that currently access the TextRenderingMode.

Fixed in <http://trac.webkit.org/projects/webkit/changeset/52889>.