Add capability to synthesize italic

Cargo.toml

@@ -10,6 +10,7 @@ repository = "https://github.com/pop-os/cosmic-text"
 rust-version = "1.65"
 
 [dependencies]
+bitflags = "2.4.1"
 cosmic_undo_2 = { version = "0.2.0", optional = true }
 fontdb = { version = "0.16.0", default-features = false }
 hashbrown = { version = "0.14.1", optional = true, default-features = false }

examples/rich-text/src/main.rs

@@ -1,8 +1,8 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
 use cosmic_text::{
-    Action, Attrs, Buffer, Color, Edit, Editor, Family, FontSystem, Metrics, Motion, Shaping,
-    Style, SwashCache, Weight,
+    Action, Attrs, Buffer, CacheKeyFlags, Color, Edit, Editor, Family, FontSystem, Metrics, Motion,
+    Shaping, Style, SwashCache, Weight,
 };
 use orbclient::{EventOption, Renderer, Window, WindowFlag};
 use std::{
@@ -63,6 +63,10 @@ fn main() {
         ("Sans-Serif Normal ", attrs),
         ("Sans-Serif Bold ", attrs.weight(Weight::BOLD)),
         ("Sans-Serif Italic ", attrs.style(Style::Italic)),
+        (
+            "Sans-Serif Fake Italic ",
+            attrs.cache_key_flags(CacheKeyFlags::FAKE_ITALIC),
+        ),
         (
             "Sans-Serif Bold Italic\n",
             attrs.weight(Weight::BOLD).style(Style::Italic),

src/attrs.rs

@@ -6,9 +6,11 @@ use alloc::{
     vec::Vec,
 };
 use core::ops::Range;
+use rangemap::RangeMap;
+
+use crate::CacheKeyFlags;
 
 pub use fontdb::{Family, Stretch, Style, Weight};
-use rangemap::RangeMap;
 
 /// Text color
 #[derive(Clone, Copy, Debug, PartialOrd, Ord, Eq, Hash, PartialEq)]
@@ -109,6 +111,7 @@ pub struct Attrs<'a> {
     pub style: Style,
     pub weight: Weight,
     pub metadata: usize,
+    pub cache_key_flags: CacheKeyFlags,
 }
 
 impl<'a> Attrs<'a> {
@@ -123,6 +126,7 @@ impl<'a> Attrs<'a> {
             style: Style::Normal,
             weight: Weight::NORMAL,
             metadata: 0,
+            cache_key_flags: CacheKeyFlags::empty(),
         }
     }
 
@@ -162,6 +166,12 @@ impl<'a> Attrs<'a> {
         self
     }
 
+    /// Set [`CacheKeyFlags`]
+    pub fn cache_key_flags(mut self, cache_key_flags: CacheKeyFlags) -> Self {
+        self.cache_key_flags = cache_key_flags;
+        self
+    }
+
     /// Check if font matches
     pub fn matches(&self, face: &fontdb::FaceInfo) -> bool {
         //TODO: smarter way of including emoji
@@ -190,6 +200,7 @@ pub struct AttrsOwned {
     pub style: Style,
     pub weight: Weight,
     pub metadata: usize,
+    pub cache_key_flags: CacheKeyFlags,
 }
 
 impl AttrsOwned {
@@ -201,6 +212,7 @@ impl AttrsOwned {
             style: attrs.style,
             weight: attrs.weight,
             metadata: attrs.metadata,
+            cache_key_flags: attrs.cache_key_flags,
         }
     }
 
@@ -212,6 +224,7 @@ impl AttrsOwned {
             style: self.style,
             weight: self.weight,
             metadata: self.metadata,
+            cache_key_flags: self.cache_key_flags,
         }
     }
 }

src/glyph_cache.rs

@@ -1,5 +1,15 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
+bitflags::bitflags! {
+    /// Flags that change rendering
+    #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+    #[repr(transparent)]
+    pub struct CacheKeyFlags: u32 {
+        /// Skew by 14 degrees to synthesize italic
+        const FAKE_ITALIC = 1;
+    }
+}
+
 /// Key for building a glyph cache
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct CacheKey {
@@ -13,6 +23,8 @@ pub struct CacheKey {
     pub x_bin: SubpixelBin,
     /// Binning of fractional Y offset
     pub y_bin: SubpixelBin,
+    /// [`CacheKeyFlags`]
+    pub flags: CacheKeyFlags,
 }
 
 impl CacheKey {
@@ -21,6 +33,7 @@ impl CacheKey {
         glyph_id: u16,
         font_size: f32,
         pos: (f32, f32),
+        flags: CacheKeyFlags,
     ) -> (Self, i32, i32) {
         let (x, x_bin) = SubpixelBin::new(pos.0);
         let (y, y_bin) = SubpixelBin::new(pos.1);
@@ -31,6 +44,7 @@ impl CacheKey {
                 font_size_bits: font_size.to_bits(),
                 x_bin,
                 y_bin,
+                flags,
             },
             x,
             y,

src/layout.rs

@@ -5,7 +5,7 @@ use core::fmt::Display;
 #[cfg(not(feature = "std"))]
 use alloc::vec::Vec;
 
-use crate::{CacheKey, Color};
+use crate::{CacheKey, CacheKeyFlags, Color};
 
 /// A laid out glyph
 #[derive(Clone, Debug)]
@@ -50,6 +50,8 @@ pub struct LayoutGlyph {
     pub color_opt: Option<Color>,
     /// Metadata from `Attrs`
     pub metadata: usize,
+    /// [`CacheKeyFlags`]
+    pub cache_key_flags: CacheKeyFlags,
 }
 
 #[derive(Clone, Debug)]
@@ -75,6 +77,7 @@ impl LayoutGlyph {
                 (self.x + x_offset) * scale + offset.0,
                 libm::truncf((self.y - y_offset) * scale + offset.1), // Hinting in Y axis
             ),
+            self.cache_key_flags,
         );
 
         PhysicalGlyph { cache_key, x, y }

src/shape.rs

@@ -13,7 +13,8 @@ use unicode_segmentation::UnicodeSegmentation;
 
 use crate::fallback::FontFallbackIter;
 use crate::{
-    Align, AttrsList, Color, Font, FontSystem, LayoutGlyph, LayoutLine, ShapePlanCache, Wrap,
+    Align, AttrsList, CacheKeyFlags, Color, Font, FontSystem, LayoutGlyph, LayoutLine,
+    ShapePlanCache, Wrap,
 };
 
 /// The shaping strategy of some text.
@@ -148,6 +149,7 @@ fn shape_fallback(
             //TODO: color should not be related to shaping
             color_opt: attrs.color_opt,
             metadata: attrs.metadata,
+            cache_key_flags: attrs.cache_key_flags,
         });
     }
 
@@ -373,6 +375,7 @@ fn shape_skip(
                     glyph_id,
                     color_opt: attrs.color_opt,
                     metadata: attrs.metadata,
+                    cache_key_flags: attrs.cache_key_flags,
                 }
             }),
     );
@@ -393,6 +396,7 @@ pub struct ShapeGlyph {
     pub glyph_id: u16,
     pub color_opt: Option<Color>,
     pub metadata: usize,
+    pub cache_key_flags: CacheKeyFlags,
 }
 
 impl ShapeGlyph {
@@ -418,6 +422,7 @@ impl ShapeGlyph {
             y_offset: self.y_offset,
             color_opt: self.color_opt,
             metadata: self.metadata,
+            cache_key_flags: self.cache_key_flags,
         }
     }
 }

src/swash.rs

@@ -7,10 +7,10 @@ use swash::scale::{image::Content, ScaleContext};
 use swash::scale::{Render, Source, StrikeWith};
 use swash::zeno::{Format, Vector};
 
-use crate::{CacheKey, Color, FontSystem, HashMap};
+use crate::{CacheKey, CacheKeyFlags, Color, FontSystem, HashMap};
 
 pub use swash::scale::image::{Content as SwashContent, Image as SwashImage};
-pub use swash::zeno::{Command, Placement};
+pub use swash::zeno::{Angle, Command, Placement, Transform};
 
 fn swash_image(
     font_system: &mut FontSystem,
@@ -49,6 +49,14 @@ fn swash_image(
     .format(Format::Alpha)
     // Apply the fractional offset
     .offset(offset)
+    .transform(if cache_key.flags.contains(CacheKeyFlags::FAKE_ITALIC) {
+        Some(Transform::skew(
+            Angle::from_degrees(14.0),
+            Angle::from_degrees(0.0),
+        ))
+    } else {
+        None
+    })
     // Render the image
     .render(&mut scaler, cache_key.glyph_id)
 }