375762 - Make platform textrun implementations return real inked glyph extents

Status: NEW

(Core :: Graphics: Text, defect)

Description

[Robert O'Callahan (:roc) (email my personal email if necessary)]

gfxTextRun exports glyph bounds information which layout needs, especially when glyph extents overflow the font-box for the glyph. The challenge is to do this fast; since glyph extent overflow is uncommon, it's probably enough to have a fast way to detect that glyph extents do not overflow the font-box. Currently we do return glyph extents on Pango (although it's probably really slow) but not on Mac or Windows. Unfortunately the platform APIs for this seem to suck.

This need not block turning on new textframe, however, since our existing code always assumes glyphs fit in the font-box so turning on new textframe would not regress in this regard.