Remove skrifa from vello's public API #747

nicoburns · 2024-11-28T00:45:06Z

The motivation for this is two-fold:

To align vello's representation of "normalized coordinates" with that of swash/parley (avoiding a boilerplatey conversion when integrating parley with vello)
To make skrifa version bumps in vello non-breaking changes.

nicoburns · 2024-11-28T00:46:43Z

vello/src/scene.rs

@@ -400,7 +400,7 @@ impl<'a> DrawGlyphs<'a> {
    }

    /// Sets the normalized design space coordinates for a variable font instance.
-    pub fn normalized_coords(mut self, coords: &[NormalizedCoord]) -> Self {
+    pub fn normalized_coords(mut self, coords: impl Iterator<Item = i16>) -> Self {


We could require ExactSizeIterator here if we want to.

I don’t think it would hurt to have a pub type NormalizedCoord = i16 in vello_encoding

What does ExactSizeIterator win us?

I think we definitely should document this slightly better, even if just to say "this will be provided by your text layout implementation". The current format is quite unactionable.

What does ExactSizeIterator win us?

Potentially slightly cheaper allocation. But I suspect size_hint will work even without ExactSizeIterator, and that even if it doesn't the cost will be small.

dfrg · 2024-11-28T01:13:10Z

Note this type is still visible from vello_encoding:

vello/vello_encoding/src/encoding.rs

Line 548 in e6ead09

pub normalized_coords: Vec<NormalizedCoord>,

This is a bit more tricky because skrifa actually wants a &[NormalizedCoord] type. We can either keep an internal buffer in the resolver and do a copy or just use bytemuck to cast the slice (font_types::F2Dot14 impls the necessary traits)

DJMcNab

Looks good. This also needs a CHANGELOG entry

examples/scenes/src/simple_text.rs

DJMcNab · 2024-11-28T09:20:56Z

examples/scenes/src/simple_text.rs

@@ -210,7 +217,7 @@ impl SimpleText {
 }

 fn to_font_ref(font: &Font) -> Option<FontRef<'_>> {
-    use vello::skrifa::raw::FileRef;
+    use skrifa::raw::FileRef;


Is there much advantage to this import being here rather than at the top of the file?

I don't think so. That was where it already was, but I've moved it to the top.

Ah, apologies. I probably didn't originally notice that this was only a change and not an addition.

DJMcNab · 2024-11-28T09:22:55Z

vello/src/scene.rs

@@ -400,7 +400,7 @@ impl<'a> DrawGlyphs<'a> {
    }

    /// Sets the normalized design space coordinates for a variable font instance.
-    pub fn normalized_coords(mut self, coords: &[NormalizedCoord]) -> Self {
+    pub fn normalized_coords(mut self, coords: impl Iterator<Item = i16>) -> Self {


What does ExactSizeIterator win us?

DJMcNab · 2024-11-28T09:23:31Z

vello/src/scene.rs

@@ -400,7 +400,7 @@ impl<'a> DrawGlyphs<'a> {
    }

    /// Sets the normalized design space coordinates for a variable font instance.
-    pub fn normalized_coords(mut self, coords: &[NormalizedCoord]) -> Self {
+    pub fn normalized_coords(mut self, coords: impl Iterator<Item = i16>) -> Self {


I think we definitely should document this slightly better, even if just to say "this will be provided by your text layout implementation". The current format is quite unactionable.

waywardmonkeys · 2024-12-04T03:09:27Z

@nicoburns Can we wrap this one up and land it? I'd like to make sure this is in our upcoming release.

Signed-off-by: Nico Burns <[email protected]>

nicoburns · 2024-12-10T08:21:39Z

How much do we still care about this being public in vello_encoding? Seems to me that it's probably less important to do semver compatible releases there? It's easy enough to change everything to i16, but it involves changing a lot of the internal uses of NormalizedCoord into i16 which seems like somewhat of a code quality regression from a readability / type safety point of view.

Signed-off-by: Nico Burns <[email protected]>

DJMcNab · 2024-12-10T10:18:02Z

I don't hate making vello_encoding intentionally not follow semver, but we'd need to do two things:

Document that being the case
Use an = dependency specification on it from Vello.

nicoburns · 2024-12-10T10:21:17Z

I don't hate making vello_encoding intentionally not follow semver, but we'd need to do two things:

Document that being the case

Use an = dependency specification on it from Vello.

My suggestion would be for vello_encoding to continue to follow semver, but to aggressively bump it's version number beyond that of the main vello crate's (as required). I feel like "you're using the low-level API, so you have to deal with breaking changes more often" is kinda reasonable, especially if the "breaking change" is just a dep bump. Also, I believe most users of vello_encoding are unlikely to have large crates.io dep trees. So conflicting versions is likely to be less of an issue.

DJMcNab · 2024-12-10T11:10:04Z

Looking again, I'm not sure that would be practical; Vello itself exposes vello_encoding as public API. I don't know the right answer here

DJMcNab · 2024-12-18T14:28:59Z

I'd probably suggest making our own NormalizedCoord type, and then as Chad says, using bytemuck as/when needed.

nicoburns added the dependencies Pull requests that update a dependency file label Nov 28, 2024

nicoburns commented Nov 28, 2024

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DJMcNab reviewed Nov 28, 2024

View reviewed changes

nicoburns added 2 commits December 10, 2024 19:58

Remove skrifa from vello's public API

6275e29

Signed-off-by: Nico Burns <[email protected]>

Move imports to top of file

aa5ee66

Add changelog entry

e847f5f

Signed-off-by: Nico Burns <[email protected]>

nicoburns force-pushed the private-skrifa branch from d7005bb to e847f5f Compare December 10, 2024 08:22

cargo fmt

e152003

Signed-off-by: Nico Burns <[email protected]>

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Remove skrifa from vello's public API #747

Remove skrifa from vello's public API #747

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DJMcNab commented Dec 18, 2024

Remove skrifa from vello's public API #747

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Remove skrifa from vello's public API #747

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