Implement subpixel glyph positioning and scaling

The latest `cosmic-text` release performs bucketing calculations after
layouting. This allows us to provide proper subpixel offsets, as well as
scale any buffer thanks to its linear layout properties.

See https://github.com/pop-os/cosmic-text/pull/143.

Cargo.toml

@@ -10,7 +10,7 @@ license = "MIT OR Apache-2.0 OR Zlib"
 [dependencies]
 wgpu = "0.16"
 etagere = "0.2.8"
-cosmic-text = "0.8"
+cosmic-text = "0.9"
 lru = "0.9"
 
 [dev-dependencies]

examples/hello-world.rs

@@ -1,6 +1,6 @@
 use glyphon::{
-    Attrs, Buffer, Color, Family, FontSystem, Metrics, Resolution, SwashCache, TextArea, TextAtlas,
-    TextBounds, TextRenderer,
+    Attrs, Buffer, Color, Family, FontSystem, Metrics, Resolution, Shaping, SwashCache, TextArea,
+    TextAtlas, TextBounds, TextRenderer,
 };
 use wgpu::{
     CommandEncoderDescriptor, CompositeAlphaMode, DeviceDescriptor, Features, Instance,
@@ -73,7 +73,7 @@ async fn run() {
     let physical_height = (height as f64 * scale_factor) as f32;
 
     buffer.set_size(&mut font_system, physical_width, physical_height);
-    buffer.set_text(&mut font_system, "Hello world! 👋\nThis is rendered with 🦅 glyphon 🦁\nThe text below should be partially clipped.\na b c d e f g h i j k l m n o p q r s t u v w x y z", Attrs::new().family(Family::SansSerif));
+    buffer.set_text(&mut font_system, "Hello world! 👋\nThis is rendered with 🦅 glyphon 🦁\nThe text below should be partially clipped.\na b c d e f g h i j k l m n o p q r s t u v w x y z", Attrs::new().family(Family::SansSerif), Shaping::Advanced);
     buffer.shape_until_scroll(&mut font_system);
 
     event_loop.run(move |event, _, control_flow| {
@@ -103,8 +103,9 @@ async fn run() {
                         },
                         [TextArea {
                             buffer: &buffer,
-                            left: 10,
-                            top: 10,
+                            left: 10.0,
+                            top: 10.0,
+                            scale: 1.0,
                             bounds: TextBounds {
                                 left: 0,
                                 top: 0,

src/lib.rs

@@ -19,7 +19,8 @@ pub use cosmic_text::{
     self, fontdb, Action, Affinity, Attrs, AttrsList, AttrsOwned, Buffer, BufferLine, CacheKey,
     Color, Command, Cursor, Edit, Editor, Family, FamilyOwned, Font, FontSystem, LayoutCursor,
     LayoutGlyph, LayoutLine, LayoutRun, LayoutRunIter, Metrics, ShapeGlyph, ShapeLine, ShapeSpan,
-    ShapeWord, Stretch, Style, SubpixelBin, SwashCache, SwashContent, SwashImage, Weight, Wrap,
+    ShapeWord, Shaping, Stretch, Style, SubpixelBin, SwashCache, SwashContent, SwashImage, Weight,
+    Wrap,
 };
 
 use etagere::AllocId;
@@ -101,9 +102,11 @@ pub struct TextArea<'a> {
     /// The buffer containing the text to be rendered.
     pub buffer: &'a Buffer,
     /// The left edge of the buffer.
-    pub left: i32,
+    pub left: f32,
     /// The top edge of the buffer.
-    pub top: i32,
+    pub top: f32,
+    /// The scaling to apply to the buffer.
+    pub scale: f32,
     /// The visible bounds of the text area. This is used to clip the text and doesn't have to
     /// match the `left` and `top` values.
     pub bounds: TextBounds,

src/text_render.rs

@@ -93,13 +93,24 @@ impl TextRenderer {
         for text_area in text_areas {
             for run in text_area.buffer.layout_runs() {
                 for glyph in run.glyphs.iter() {
-                    if atlas.mask_atlas.glyph_cache.contains(&glyph.cache_key) {
-                        atlas.mask_atlas.promote(glyph.cache_key);
-                    } else if atlas.color_atlas.glyph_cache.contains(&glyph.cache_key) {
-                        atlas.color_atlas.promote(glyph.cache_key);
+                    let physical_glyph =
+                        glyph.physical((text_area.left, text_area.top), text_area.scale);
+
+                    if atlas
+                        .mask_atlas
+                        .glyph_cache
+                        .contains(&physical_glyph.cache_key)
+                    {
+                        atlas.mask_atlas.promote(physical_glyph.cache_key);
+                    } else if atlas
+                        .color_atlas
+                        .glyph_cache
+                        .contains(&physical_glyph.cache_key)
+                    {
+                        atlas.color_atlas.promote(physical_glyph.cache_key);
                     } else {
                         let Some(image) = cache
-                            .get_image_uncached(font_system, glyph.cache_key) else { continue };
+                            .get_image_uncached(font_system, physical_glyph.cache_key) else { continue };
 
                         let content_type = match image.content {
                             SwashContent::Color => ContentType::Color,
@@ -178,7 +189,7 @@ impl TextRenderer {
                         };
 
                         inner.put(
-                            glyph.cache_key,
+                            physical_glyph.cache_key,
                             GlyphDetails {
                                 width: width as u16,
                                 height: height as u16,
@@ -190,11 +201,11 @@ impl TextRenderer {
                         );
                     }
 
-                    let details = atlas.glyph(&glyph.cache_key).unwrap();
+                    let details = atlas.glyph(&physical_glyph.cache_key).unwrap();
 
-                    let mut x = glyph.x_int + details.left as i32 + text_area.left;
-                    let mut y =
-                        run.line_y as i32 + glyph.y_int - details.top as i32 + text_area.top;
+                    let mut x = physical_glyph.x + details.left as i32;
+                    let mut y = (run.line_y * text_area.scale).round() as i32 + physical_glyph.y
+                        - details.top as i32;
 
                     let (mut atlas_x, mut atlas_y, content_type) = match details.gpu_cache {
                         GpuCacheStatus::InAtlas { x, y, content_type } => (x, y, content_type),