Embolden

[behdad]

Fixes #3883

[behdad]

Todo:

• Relicense the code from FreeType authors (contacted),
• Docs.
• Add hb_font_t API and hook it up. Currently embolden amount hardcoded.
• Adapt advances
• Adapt shaping to it. No one else does. Ignore for now.
• Figure out if parent-draw adapter needs any changes; well. We probably are not going to change bolding between parent/child... Or maybe we do. Humm. Emboldening happens at the hb-ot-font layer; seems like it wouldn't need any changes there.
• Glyph extents.
• Font extents. The rest of metrics we're not going to try.

[matthiasclasen]

I've added some docs.

[behdad]

@khaledhosny rightly pointed out that adjusting the advance-widths unfortunately breaks Arabic fonts that use rounded edges for their connecting strokes. We can't ignore that unfortunately. So I'm stuck as to how to proceed. Khaled also mentioned that in LibreOffice he uses unadjusted advance-widths and so far no one complained.

If using unadjusted advance-widths though, I think we should NOT shift the glyph shape horizontally then. Which I can do. But then we should also unshift the FreeType outlines in hb-ft. I think we should still shift them vertically such that they sit on the baseline.

All of this ends up who knows where in vertical writing....

[khaledhosny]

@khaledhosny rightly pointed out that adjusting the advance-widths unfortunately breaks Arabic fonts that use rounded edges for their connecting strokes. We can't ignore that unfortunately. So I'm stuck as to how to proceed. Khaled also mentioned that in LibreOffice he uses unadjusted advance-widths and so far no one complained.

If using unadjusted advance-widths though, I think we should NOT shift the glyph shape horizontally then. Which I can do. But then we should also unshift the FreeType outlines in hb-ft. I think we should still shift them vertically such that they sit on the baseline.

All of this ends up who knows where in vertical writing....

There are other cases where keeping advance width is desired like monospace fonts or using emboldening to achieve something like grade. I think it might be worth while to add an option or a flag to control advance adjustment and shift in both directions.

[behdad]

There are other cases where keeping advance width is desired like monospace fonts or using emboldening to achieve something like grade. I think it might be worth while to add an option or a flag to control advance adjustment and shift in both directions.

Matthias had the same idea. Okay I'm convinced.

[behdad]

Okay so then to hb-view I'll add --font-bold and --font-grade?

[behdad]

@khaledhosny @matthiasclasen How does this look?

[behdad]

• Glyph extents.
• Font extents. The rest of metrics we're not going to try.

Working on these.

[behdad]

Should grade shift glyphs up or not? Currently it does. @khaledhosny @davelab6

[behdad]

• Glyph extents.
• Font extents. The rest of metrics we're not going to try.

Working on these.

Done. I think this is good to land now. I can work on hb-ot-metrics later.

[matthiasclasen]

Looks good to me apart from those two comments.

[matthiasclasen]

Thanks for the explanation!