Fast specialized CPU glyph rasterization

[nicoburns]

emilk/egui#8093 notes that glyph rasterization in egui is slower using skrifa+vello_cpu compared to the old rendering using ab_glyph. To some extent that is expected and reflects that skrifa+vello_cpu renders glyphs at higher quality.

Nevertheless, vello_cpu is a generalized rasterisation pipeline that is slower than it could be for the task of rendering glyph outlines, and we may want to consider creating an optimised pipeline specifically for glyph rasterization.

I am assuming that this rasterizer would be only for regular "outline" glyphs and COLR glyphs would still use the regular vello_cpu pipeline. We may also want to consider whether we could/should support subpixel rendering.

Prior Art

Potential sources of inspiration for such a renderer

• Raph's https://github.com/raphlinus/font-rs (blog post)
• Chad's https://github.com/dfrg/zeno (used in swash)
• Behdad's https://github.com/harfbuzz/harfbuzz/blob/main/src/hb-raster-draw.cc (zulip thread)
• FreeType's rasterizer
• Vello CPU

[LaurenzV]

Yep, I had the same thought on the weekend, I agree we should consider having something like this. 👍

[waywardmonkeys]

I'm in the process of building things where I wouldn't be using glifo and will be building glyph atlases and rendering from them ... so this is something on my mind as well.