Pure Rust font stack for wr_glyph_rasterizer

[declantsien]

#498 (comment)

[2e0byo]

Isn't this down to automatic composition not being implemented ?

[declantsien]

2e0byo ***@***.***> writes:

Isn't this down to automatic composition [not being implemented](https://github.com/emacs-ng/emacs-ng/blob/master/rust_src/crates/webrender/src/draw_canvas.rs#L434) ? -- Reply to this email directly or view it on GitHub: #498 (comment) You are receiving this because you authored the thread. Message ID: ***@***.***>

Seems like that is the case.

[declantsien]

Hit this WR bug. WebRender currently does not work with Noto Color Emoji.

2023-03-15T02:04:03.872358Z ERROR wr_glyph_rasterizer::platform::unix::font: Unable to set glyph size and transform: 23
2023-03-15T02:04:03.872373Z DEBUG wr_glyph_rasterizer::platform::unix::font:    [662] for size 16.0 and scale (1.0, 1.0) from font FontKey(IdNamespace(1), 5)
2023-03-15T02:04:03.872393Z ERROR wr_glyph_rasterizer::platform::unix::font: Unable to set glyph size and transform: 23
2023-03-15T02:04:03.872404Z DEBUG wr_glyph_rasterizer::platform::unix::font:    [260158] for size 16.0 and scale (1.0, 1.0) from font FontKey(IdNamespace(1), 5)```

[declantsien]

Code path for color font is not limited to glyph automatic composite.
It used for glyph_type::CHAR_GLYPH too.

Better if WebRender GlyphInstance adds supports for this, otherwise we have to manually draw font png/svg images.

While waiting for WebRender adding support for Color Font. I am happy with just disable Noto Color Emoji for now.

[declantsien]

I recently realized that WebRender has a hard C dependencies (freetype2/harfbuzz), while we'd prefer font stack using Rust(fontdb/ttf_parser/rustybuzz/fontdue/swash etc).

I've experimenting with replacing WebRender wr_glyph_rasterizer with fontdue. It turns out doable. My WebRender branch using fontdue is here and ng branch here.

Tasks:

• Make sure wr_glyph_rasterizer fontdue backend works well with WebRender's distribute_across_threads

• Patch fontdue to work with ttf_parser's glyph_raster_image and glyph_svg_image. This is for color emojis.
  Working since declantsien@0e8429e

• Patch fontdue for font shaping(ligatures etc) support
  Ligature support- pairing with other libraries mooman219/fontdue#127

• What about WebRender Mono FontRenderMode

• Some WR FontInstanceFlags is not implemented, also we haven't use them in Emacs

There are some font concepts I am not sure whether there are involved here.

• Font kerning ? https://github.com/keiya01/font-kerning.git
• Glyph cache using GPU(atlas?) https://github.com/ryanisaacg/elefont.git
• Text layout is not necessary since Emacs redisplay is doing all the calculation?
  ...

[declantsien]

png/svg fonts is working using patched wr_glyph_rasterizer.

[rice7th]

perhaps Cosmic text?

[declantsien]

perhaps Cosmic text?

Cosmic text doesn't really fit into Emacs IMO. Emacs layout text itself.
However the glyph rendering library swash they use is what we need which also support complex text shaping.
I manage to make the emoji and shaping working here #564.

Choosing swash over fontdue which I mentioned in other comments, is that fontdue doesn't support emoji rendering, also we have to find another rust shaping library.

Interestingly, we have this elisp OTF/TTF font loader and renderer which is inspired by fontdue.

[declantsien]

[rice7th]

Allsortrs by yeslogic seems to be a powerful shaping library

[declantsien]

Allsortrs by yeslogic seems to be a powerful shaping library

I think we wouldn't mind having a new Emacs font driver implemented in Allsort!
If someone is willing to write the code for it 🙂

[rice7th]

Oh well I don't have that much experience with font shaping libraries 😅 but if I find enough time maybe this summer I can give it a look