Export for GlyphExtents and UnicodeBuffer internals

[asibahi]

Hello

I am trying to redo the wasm shaper for HarfRust but as an external crate on top of it and skrifa. I am still on the phase of trying to port the code and I have not kept up with the changes from rustybuzz to HarfRust.

A few roadblocks are the following:

1. Getting the GlyphExtents data: One of the functions require Glyph Extents. This does not seem to be exposed. It might be just as simple as adding it to a pub use to lib.rs.

2. Getting the internals of UnicodeBuffer. This needs to be reset this from raw data coming from the module. IF there is a better way to do this I am all ears.

store_data.buffer.len = buffer.length as usize;

store_data.buffer.info.clear();
store_data.buffer.info.extend_from_slice(bytemuck::cast_slice(
	&mem_data[buffer.info as usize..buffer.info as usize + array_length],
));

store_data.buffer.pos.clear();
store_data.buffer.pos.extend_from_slice(bytemuck::cast_slice(
	&mem_data[buffer.position as usize..buffer.position as usize + array_length],
));

3. Last and least: hb_font_t, exported as Shaper, seems to have lost the inquiries about specific glyphs and tables. I am not quite sure how to access these. (I have not thought about this too much, and it might be as simple as just passing the FontRef from read_fonts separately.

Am I missing something obvious in regards to these points or are they something the crate can export?

[behdad]

Hello hello.

Before you spend much time on this, I like to update you on my current plans for the wasm shaper. Basically, a full rehaul.

1. Get rid of the font_t abstraction. Everything will be in font units, like the rest of the font.
2. Rename the API to use a prefix. Not sure what. Following up in Prefix wasm objects and functions with *something* harfbuzz#4457

[asibahi]

My immediate current plan is to just port the impl. I want to experiment with the API a bit too at a later stage.

[dfrg]

I’d definitely like to include whatever is needed to support this. What if we add a new RawBuffer type that exposes the necessary operations? Perhaps with the caveat that this lacks the stability guarantees of the other buffer types.

As for metrics, I’d prefer not to expose any of the internal methods right now. I’m currently working on adding more comprehensive support for this to read-fonts and we also want to allow metrics overrides in harfrust to handle things like hinting. Hopefully these changes will be sufficient to meet the needs of the wasm shaper. In the meantime, I’d suggest using skrifa/read-fonts directly.

[asibahi]

I am unclear on how I would get the hb_glyph_extents_t data from skrifa or read_fonts. It seems internal to HR?

[dfrg]

Skrifa has the GlyphMetrics::bounds method which is currently more accurate than the internal extents code we use in HR since it supports CFF fonts and variations.