Created attachment 86179 [details]
When using a font with non-integer advances, there are sometimes gaps in the selection highlight between line boxes or between line box and gap rects. You can see this by highlighting text in the attached test case. I’ve also seen overlapping highlights and sometimes leftover highlight bits when clearing the selection.
Created attachment 91812 [details]
Account for non-integral anchor point coordinates
Fixed in r85411 <http://trac.webkit.org/changeset/85411>