[vello_encoding] Move the encoding module into its own crate

This change moves the vello encoding logic to a new crate under
crates/encoding. Combined with the `vello_shaders` crate, this enables
lightweight integration of the Vello pipelines into renderers that don't
depend on wgpu (or perhaps written in languages other than Rust).

The Scene/Fragment API currently remain the vello crate.

Cargo.toml

@@ -2,6 +2,7 @@
 resolver = "2"
 
 members = [
+    "crates/encoding",
     "crates/shaders",
 
     "integrations/vello_svg",
@@ -40,17 +41,20 @@ hot_reload = []
 buffer_labels = []
 
 [dependencies]
+bytemuck = { workspace = true }
+fello = { workspace = true }
+peniko = { workspace = true }
 wgpu = { workspace = true }
 raw-window-handle = "0.5"
 futures-intrusive = "0.5.0"
 parking_lot = "0.12"
-bytemuck = { version = "1.12.1", features = ["derive"] }
 smallvec = "1.8.0"
-fello = { git = "https://github.com/dfrg/fount", rev = "58a284eaae67512fb61cf76177c5d33238d79cb1" }
-peniko = { git = "https://github.com/linebender/peniko", rev = "cafdac9a211a0fb2fec5656bd663d1ac770bcc81" }
-guillotiere = "0.6.2"
+vello_encoding = { path = "crates/encoding" }
 
 [workspace.dependencies]
+bytemuck = { version = "1.12.1", features = ["derive"] }
+fello = { git = "https://github.com/dfrg/fount", rev = "58a284eaae67512fb61cf76177c5d33238d79cb1" }
+peniko = { git = "https://github.com/linebender/peniko", rev = "cafdac9a211a0fb2fec5656bd663d1ac770bcc81" }
 wgpu = "0.15"
 
 # Used for examples

crates/encoding/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "vello_encoding"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+bytemuck = { workspace = true }
+fello = { workspace = true }
+peniko = { workspace = true }
+guillotiere = "0.6.2"

crates/encoding/src/encoding.rs

@@ -14,11 +14,9 @@
 //
 // Also licensed under MIT license, at your choice.
 
-use crate::encoding::DrawImage;
-
 use super::{
-    resolve::Patch, DrawColor, DrawLinearGradient, DrawRadialGradient, DrawTag, Glyph, GlyphRun,
-    PathEncoder, PathTag, Transform,
+    resolve::Patch, DrawColor, DrawImage, DrawLinearGradient, DrawRadialGradient, DrawTag, Glyph,
+    GlyphRun, PathEncoder, PathTag, Transform,
 };
 
 use fello::NormalizedCoord;

crates/encoding/src/glyph_cache.rs

@@ -59,11 +59,11 @@ impl GlyphCache {
                 Style::Fill(Fill::EvenOdd) => encoding_cache.encode_linewidth(-2.0),
                 Style::Stroke(stroke) => encoding_cache.encode_linewidth(stroke.width),
             }
-            let mut path = crate::glyph::PathEncoderPen(encoding_cache.encode_path(is_fill));
+            let mut path = encoding_cache.encode_path(is_fill);
             scaler
                 .outline(GlyphId::new(key.glyph_id as u16), &mut path)
                 .ok()?;
-            if path.0.finish(false) == 0 {
+            if path.finish(false) == 0 {
                 return None;
             }
             let end = encoding_cache.stream_offsets();

crates/encoding/src/path.rs

@@ -381,3 +381,25 @@ impl<'a> PathEncoder<'a> {
         self.n_encoded_segments
     }
 }
+
+impl fello::scale::Pen for PathEncoder<'_> {
+    fn move_to(&mut self, x: f32, y: f32) {
+        self.move_to(x, y)
+    }
+
+    fn line_to(&mut self, x: f32, y: f32) {
+        self.line_to(x, y)
+    }
+
+    fn quad_to(&mut self, cx0: f32, cy0: f32, x: f32, y: f32) {
+        self.quad_to(cx0, cy0, x, y)
+    }
+
+    fn curve_to(&mut self, cx0: f32, cy0: f32, cx1: f32, cy1: f32, x: f32, y: f32) {
+        self.cubic_to(cx0, cy0, cx1, cy1, x, y)
+    }
+
+    fn close(&mut self) {
+        self.close()
+    }
+}

crates/encoding/src/resolve.rs

@@ -25,7 +25,6 @@ use super::{
     ramp_cache::{RampCache, Ramps},
     DrawTag, Encoding, PathTag, StreamOffsets, Transform,
 };
-use crate::shaders;
 
 /// Layout of a packed encoding.
 #[derive(Clone, Copy, Debug, Default, Zeroable, Pod)]
@@ -161,6 +160,7 @@ impl Resolver {
         &'a mut self,
         encoding: &Encoding,
         packed: &mut Vec<u8>,
+        workgroup_size: u32,
     ) -> (Layout, Ramps<'a>, Images<'a>) {
         let sizes = self.resolve_patches(encoding);
         self.resolve_pending_images();
@@ -172,7 +172,7 @@ impl Resolver {
         // Compute size of data buffer
         let n_path_tags =
             encoding.path_tags.len() + sizes.path_tags + encoding.n_open_clips as usize;
-        let path_tag_padded = align_up(n_path_tags, 4 * shaders::PATHTAG_REDUCE_WG);
+        let path_tag_padded = align_up(n_path_tags, 4 * workgroup_size);
         let capacity = path_tag_padded
             + slice_size_in_bytes(&encoding.path_data, sizes.path_data)
             + slice_size_in_bytes(

examples/scenes/Cargo.toml

@@ -12,6 +12,7 @@ repository.workspace = true
 
 [dependencies]
 vello = { path = "../../" }
+vello_encoding = { path = "../../crates/encoding" }
 vello_svg = { path = "../../integrations/vello_svg" }
 anyhow = { workspace = true }
 clap = { workspace = true, features = ["derive"] }

examples/scenes/src/simple_text.rs

@@ -17,7 +17,6 @@
 use std::sync::Arc;
 
 use vello::{
-    encoding::Glyph,
     fello::meta::MetadataProvider,
     fello::raw::FontRef,
     glyph::GlyphContext,
@@ -25,6 +24,7 @@ use vello::{
     peniko::{Blob, Brush, BrushRef, Font, StyleRef},
     SceneBuilder,
 };
+use vello_encoding::Glyph;
 
 // This is very much a hack to get things working.
 // On Windows, can set this to "c:\\Windows\\Fonts\\seguiemj.ttf" to get color emoji

src/glyph.rs

@@ -16,18 +16,17 @@
 
 //! Support for glyph rendering.
 
-use fello::scale::Pen;
-
-use crate::encoding::{Encoding, PathEncoder};
 use crate::scene::{SceneBuilder, SceneFragment};
-use peniko::kurbo::Affine;
-use peniko::{Brush, Color, Fill, Style};
-
-use fello::{
-    raw::types::GlyphId,
-    raw::FontRef,
-    scale::{Context, Scaler},
-    FontKey, Setting, Size,
+use {
+    fello::{
+        raw::types::GlyphId,
+        raw::FontRef,
+        scale::{Context, Pen, Scaler},
+        FontKey, Setting, Size,
+    },
+    peniko::kurbo::Affine,
+    peniko::{Brush, Color, Fill, Style},
+    vello_encoding::Encoding,
 };
 
 /// General context for creating scene fragments for glyph outlines.
@@ -105,9 +104,9 @@ impl<'a> GlyphProvider<'a> {
             Style::Fill(Fill::EvenOdd) => encoding.encode_linewidth(-2.0),
             Style::Stroke(stroke) => encoding.encode_linewidth(stroke.width),
         }
-        let mut path = PathEncoderPen(encoding.encode_path(matches!(style, Style::Fill(_))));
+        let mut path = encoding.encode_path(matches!(style, Style::Fill(_)));
         self.scaler.outline(GlyphId::new(gid), &mut path).ok()?;
-        if path.0.finish(false) != 0 {
+        if path.finish(false) != 0 {
             Some(())
         } else {
             None
@@ -144,27 +143,3 @@ impl Pen for BezPathPen {
         self.0.close_path()
     }
 }
-
-pub(crate) struct PathEncoderPen<'a>(pub PathEncoder<'a>);
-
-impl Pen for PathEncoderPen<'_> {
-    fn move_to(&mut self, x: f32, y: f32) {
-        self.0.move_to(x, y)
-    }
-
-    fn line_to(&mut self, x: f32, y: f32) {
-        self.0.line_to(x, y)
-    }
-
-    fn quad_to(&mut self, cx0: f32, cy0: f32, x: f32, y: f32) {
-        self.0.quad_to(cx0, cy0, x, y)
-    }
-
-    fn curve_to(&mut self, cx0: f32, cy0: f32, cx1: f32, cy1: f32, x: f32, y: f32) {
-        self.0.cubic_to(cx0, cy0, cx1, cy1, x, y)
-    }
-
-    fn close(&mut self) {
-        self.0.close()
-    }
-}

src/render.rs

@@ -1,13 +1,15 @@
 //! Take an encoded scene and create a graph to render it
 
-use bytemuck::{Pod, Zeroable};
-
 use crate::{
-    encoding::{Config, Encoding, Layout},
     engine::{BufProxy, ImageFormat, ImageProxy, Recording, ResourceProxy},
     shaders::{self, FullShaders, Shaders},
     RenderParams, Scene,
 };
+use {
+    bytemuck::{Pod, Zeroable},
+    vello_encoding::{Config, Encoding, Layout},
+};
+
 
 /// State for a render in progress.
 pub struct Render {
@@ -213,11 +215,11 @@ impl Render {
         params: &RenderParams,
         robust: bool,
     ) -> Recording {
-        use crate::encoding::Resolver;
+        use vello_encoding::Resolver;
         let mut recording = Recording::default();
         let mut resolver = Resolver::new();
         let mut packed = vec![];
-        let (layout, ramps, images) = resolver.resolve(encoding, &mut packed);
+        let (layout, ramps, images) = resolver.resolve(encoding, &mut packed, shaders::PATHTAG_REDUCE_WG);
         let gradient_image = if ramps.height == 0 {
             ResourceProxy::new_image(1, 1, ImageFormat::Rgba8)
         } else {
@@ -245,7 +247,7 @@ impl Render {
         let new_height = next_multiple_of(params.height, 16);
 
         let info_size = layout.bin_data_start;
-        let config = crate::encoding::Config {
+        let config = vello_encoding::Config {
             width_in_tiles: new_width / 16,
             height_in_tiles: new_height / 16,
             target_width: params.width,

src/scene.rs

@@ -17,8 +17,7 @@
 use fello::NormalizedCoord;
 use peniko::kurbo::{Affine, Rect, Shape};
 use peniko::{BlendMode, BrushRef, Color, Fill, Font, Image, Stroke, StyleRef};
-
-use crate::encoding::{Encoding, Glyph, GlyphRun, Patch, Transform};
+use vello_encoding::{Encoding, Glyph, GlyphRun, Patch, Transform};
 
 /// Encoded definition of a scene and associated resources.
 #[derive(Default)]