Resolve variations on fallback faces

vendor/cosmic-text/src/attrs.rs

@@ -331,6 +331,14 @@ pub struct Attrs<'a> {
     /// A specific database face selected by the caller. Font fallback remains
     /// available when that face does not contain a requested glyph.
     pub font_id_opt: Option<fontdb::ID>,
+    /// High-level CSS `font-weight` coordinate, applied only when the actual
+    /// shaped face provides a `wght` axis.
+    pub font_weight_axis_opt: Option<VariationValue>,
+    /// Automatic optical-size coordinate derived from the used font size.
+    /// `None` represents `font-optical-sizing: none`.
+    pub font_optical_size_opt: Option<VariationValue>,
+    /// Whether high-level font style requests an italic variable instance.
+    pub font_italic_axis: bool,
     pub stretch: Stretch,
     pub style: Style,
     pub weight: Weight,
@@ -352,6 +360,9 @@ impl<'a> Attrs<'a> {
             color_opt: None,
             family: Family::SansSerif,
             font_id_opt: None,
+            font_weight_axis_opt: None,
+            font_optical_size_opt: None,
+            font_italic_axis: false,
             stretch: Stretch::Normal,
             style: Style::Normal,
             weight: Weight::NORMAL,
@@ -382,6 +393,21 @@ impl<'a> Attrs<'a> {
         self
     }
 
+    pub fn font_weight_axis(mut self, value: f32) -> Self {
+        self.font_weight_axis_opt = Some(VariationValue(value));
+        self
+    }
+
+    pub fn font_optical_size(mut self, value: f32) -> Self {
+        self.font_optical_size_opt = Some(VariationValue(value));
+        self
+    }
+
+    pub fn font_italic_axis(mut self, italic: bool) -> Self {
+        self.font_italic_axis = italic;
+        self
+    }
+
     /// Set [Stretch]
     pub fn stretch(mut self, stretch: Stretch) -> Self {
         self.stretch = stretch;
@@ -453,6 +479,9 @@ impl<'a> Attrs<'a> {
     pub fn compatible(&self, other: &Self) -> bool {
         self.family == other.family
             && self.font_id_opt == other.font_id_opt
+            && self.font_weight_axis_opt == other.font_weight_axis_opt
+            && self.font_optical_size_opt == other.font_optical_size_opt
+            && self.font_italic_axis == other.font_italic_axis
             && self.stretch == other.stretch
             && self.style == other.style
             && self.weight == other.weight
@@ -487,6 +516,9 @@ pub struct AttrsOwned {
     pub color_opt: Option<Color>,
     pub family_owned: FamilyOwned,
     pub font_id_opt: Option<fontdb::ID>,
+    pub font_weight_axis_opt: Option<VariationValue>,
+    pub font_optical_size_opt: Option<VariationValue>,
+    pub font_italic_axis: bool,
     pub stretch: Stretch,
     pub style: Style,
     pub weight: Weight,
@@ -505,6 +537,9 @@ impl AttrsOwned {
             color_opt: attrs.color_opt,
             family_owned: FamilyOwned::new(attrs.family),
             font_id_opt: attrs.font_id_opt,
+            font_weight_axis_opt: attrs.font_weight_axis_opt,
+            font_optical_size_opt: attrs.font_optical_size_opt,
+            font_italic_axis: attrs.font_italic_axis,
             stretch: attrs.stretch,
             style: attrs.style,
             weight: attrs.weight,
@@ -522,6 +557,9 @@ impl AttrsOwned {
             color_opt: self.color_opt,
             family: self.family_owned.as_family(),
             font_id_opt: self.font_id_opt,
+            font_weight_axis_opt: self.font_weight_axis_opt,
+            font_optical_size_opt: self.font_optical_size_opt,
+            font_italic_axis: self.font_italic_axis,
             stretch: self.stretch,
             style: self.style,
             weight: self.weight,

vendor/cosmic-text/src/layout.rs

@@ -22,6 +22,14 @@ pub struct LayoutGlyph {
     pub font_id: fontdb::ID,
     /// Font id of the glyph
     pub glyph_id: u16,
+    /// Whether the selected font face has variation axes.
+    pub font_is_variable: bool,
+    /// Automatic `wght` axis value requested by the span.
+    pub font_weight_axis_opt: Option<f32>,
+    /// Automatic `opsz` axis value requested by the span.
+    pub font_optical_size_opt: Option<f32>,
+    /// Whether the span requests an italic variation axis.
+    pub font_italic_axis: bool,
     /// X offset of hitbox
     pub x: f32,
     /// Y offset of hitbox

vendor/cosmic-text/src/shape.rs

@@ -144,10 +144,41 @@ fn shape_fallback(
     // requests non-default variation coordinates, then use the varied face for
     // metrics, plan construction, and shaping so advances and glyph selection
     // are derived from the same instance.
-    let varied_face = if attrs.font_variations.is_empty() {
+    let varied_face = if !font.rustybuzz().is_variable()
+        || (attrs.font_variations.is_empty()
+            && attrs.font_weight_axis_opt.is_none()
+            && attrs.font_optical_size_opt.is_none()
+            && !attrs.font_italic_axis)
+    {
         None
     } else {
         let mut face = font.rustybuzz().clone();
+        if let Some(value) = attrs
+            .font_weight_axis_opt
+            .map(|value| value.0)
+            .filter(|value| value.is_finite())
+        {
+            let _ = face.set_variation(rustybuzz::ttf_parser::Tag::from_bytes(b"wght"), value);
+        }
+        if let Some(value) = attrs
+            .font_optical_size_opt
+            .map(|value| value.0)
+            .filter(|value| value.is_finite())
+        {
+            let _ = face.set_variation(rustybuzz::ttf_parser::Tag::from_bytes(b"opsz"), value);
+        }
+        if attrs.font_italic_axis {
+            let italic = rustybuzz::ttf_parser::Tag::from_bytes(b"ital");
+            if face
+                .variation_axes()
+                .into_iter()
+                .any(|axis| axis.tag == italic)
+            {
+                let _ = face.set_variation(italic, 1.0);
+            } else {
+                let _ = face.set_variation(rustybuzz::ttf_parser::Tag::from_bytes(b"slnt"), -14.0);
+            }
+        }
         for variation in attrs
             .font_variations
             .iter()
@@ -257,6 +288,10 @@ fn shape_fallback(
             font_monospace_em_width: font.monospace_em_width(),
             font_id: font.id(),
             glyph_id: info.glyph_id.try_into().expect("failed to cast glyph ID"),
+            font_is_variable: face.is_variable(),
+            font_weight_axis_opt: attrs.font_weight_axis_opt.map(|value| value.0),
+            font_optical_size_opt: attrs.font_optical_size_opt.map(|value| value.0),
+            font_italic_axis: attrs.font_italic_axis,
             //TODO: color should not be related to shaping
             color_opt: attrs.color_opt,
             metadata: attrs.metadata,
@@ -539,6 +574,7 @@ fn shape_skip(
         .expect("no default font found");
     let font_id = font.id();
     let font_monospace_em_width = font.monospace_em_width();
+    let font_is_variable = font.rustybuzz().is_variable();
     let font = font.as_swash();
 
     let charmap = font.charmap();
@@ -569,6 +605,10 @@ fn shape_skip(
                     font_monospace_em_width,
                     font_id,
                     glyph_id,
+                    font_is_variable,
+                    font_weight_axis_opt: attrs.font_weight_axis_opt.map(|value| value.0),
+                    font_optical_size_opt: attrs.font_optical_size_opt.map(|value| value.0),
+                    font_italic_axis: attrs.font_italic_axis,
                     color_opt: attrs.color_opt,
                     metadata: attrs.metadata,
                     cache_key_flags: attrs.cache_key_flags,
@@ -592,6 +632,10 @@ pub struct ShapeGlyph {
     pub font_monospace_em_width: Option<f32>,
     pub font_id: fontdb::ID,
     pub glyph_id: u16,
+    pub font_is_variable: bool,
+    pub font_weight_axis_opt: Option<f32>,
+    pub font_optical_size_opt: Option<f32>,
+    pub font_italic_axis: bool,
     pub color_opt: Option<Color>,
     pub metadata: usize,
     pub cache_key_flags: CacheKeyFlags,
@@ -615,6 +659,10 @@ impl ShapeGlyph {
             line_height_opt,
             font_id: self.font_id,
             glyph_id: self.glyph_id,
+            font_is_variable: self.font_is_variable,
+            font_weight_axis_opt: self.font_weight_axis_opt,
+            font_optical_size_opt: self.font_optical_size_opt,
+            font_italic_axis: self.font_italic_axis,
             x,
             y,
             w,