Cache rustybuzz shape plans.

src/glyph_cache.rs

@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+/// Key for building a glyph cache
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub struct CacheKey {
+    /// Font ID
+    pub font_id: fontdb::ID,
+    /// Glyph ID
+    pub glyph_id: u16,
+    /// `f32` bits of font size
+    pub font_size_bits: u32,
+    /// Binning of fractional X offset
+    pub x_bin: SubpixelBin,
+    /// Binning of fractional Y offset
+    pub y_bin: SubpixelBin,
+}
+
+impl CacheKey {
+    pub fn new(
+        font_id: fontdb::ID,
+        glyph_id: u16,
+        font_size: f32,
+        pos: (f32, f32),
+    ) -> (Self, i32, i32) {
+        let (x, x_bin) = SubpixelBin::new(pos.0);
+        let (y, y_bin) = SubpixelBin::new(pos.1);
+        (
+            Self {
+                font_id,
+                glyph_id,
+                font_size_bits: font_size.to_bits(),
+                x_bin,
+                y_bin,
+            },
+            x,
+            y,
+        )
+    }
+}
+
+/// Binning of subpixel position for cache optimization
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub enum SubpixelBin {
+    Zero,
+    One,
+    Two,
+    Three,
+}
+
+impl SubpixelBin {
+    pub fn new(pos: f32) -> (i32, Self) {
+        let (fract, truncf) = libm::modff(pos);
+        let trunc = truncf as i32;
+        if pos.is_sign_negative() {
+            if fract > -0.125 {
+                (trunc, Self::Zero)
+            } else if fract > -0.375 {
+                (trunc - 1, Self::Three)
+            } else if fract > -0.625 {
+                (trunc - 1, Self::Two)
+            } else if fract > -0.875 {
+                (trunc - 1, Self::One)
+            } else {
+                (trunc - 1, Self::Zero)
+            }
+        } else {
+            #[allow(clippy::collapsible_else_if)]
+            if fract < 0.125 {
+                (trunc, Self::Zero)
+            } else if fract < 0.375 {
+                (trunc, Self::One)
+            } else if fract < 0.625 {
+                (trunc, Self::Two)
+            } else if fract < 0.875 {
+                (trunc, Self::Three)
+            } else {
+                (trunc + 1, Self::Zero)
+            }
+        }
+    }
+
+    pub fn as_float(&self) -> f32 {
+        match self {
+            Self::Zero => 0.0,
+            Self::One => 0.25,
+            Self::Two => 0.5,
+            Self::Three => 0.75,
+        }
+    }
+}
+
+#[test]
+fn test_subpixel_bins() {
+    // POSITIVE TESTS
+
+    // Maps to 0.0
+    assert_eq!(SubpixelBin::new(0.0), (0, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(0.124), (0, SubpixelBin::Zero));
+
+    // Maps to 0.25
+    assert_eq!(SubpixelBin::new(0.125), (0, SubpixelBin::One));
+    assert_eq!(SubpixelBin::new(0.25), (0, SubpixelBin::One));
+    assert_eq!(SubpixelBin::new(0.374), (0, SubpixelBin::One));
+
+    // Maps to 0.5
+    assert_eq!(SubpixelBin::new(0.375), (0, SubpixelBin::Two));
+    assert_eq!(SubpixelBin::new(0.5), (0, SubpixelBin::Two));
+    assert_eq!(SubpixelBin::new(0.624), (0, SubpixelBin::Two));
+
+    // Maps to 0.75
+    assert_eq!(SubpixelBin::new(0.625), (0, SubpixelBin::Three));
+    assert_eq!(SubpixelBin::new(0.75), (0, SubpixelBin::Three));
+    assert_eq!(SubpixelBin::new(0.874), (0, SubpixelBin::Three));
+
+    // Maps to 1.0
+    assert_eq!(SubpixelBin::new(0.875), (1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(0.999), (1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(1.0), (1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(1.124), (1, SubpixelBin::Zero));
+
+    // NEGATIVE TESTS
+
+    // Maps to 0.0
+    assert_eq!(SubpixelBin::new(-0.0), (0, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(-0.124), (0, SubpixelBin::Zero));
+
+    // Maps to 0.25
+    assert_eq!(SubpixelBin::new(-0.125), (-1, SubpixelBin::Three));
+    assert_eq!(SubpixelBin::new(-0.25), (-1, SubpixelBin::Three));
+    assert_eq!(SubpixelBin::new(-0.374), (-1, SubpixelBin::Three));
+
+    // Maps to 0.5
+    assert_eq!(SubpixelBin::new(-0.375), (-1, SubpixelBin::Two));
+    assert_eq!(SubpixelBin::new(-0.5), (-1, SubpixelBin::Two));
+    assert_eq!(SubpixelBin::new(-0.624), (-1, SubpixelBin::Two));
+
+    // Maps to 0.75
+    assert_eq!(SubpixelBin::new(-0.625), (-1, SubpixelBin::One));
+    assert_eq!(SubpixelBin::new(-0.75), (-1, SubpixelBin::One));
+    assert_eq!(SubpixelBin::new(-0.874), (-1, SubpixelBin::One));
+
+    // Maps to 1.0
+    assert_eq!(SubpixelBin::new(-0.875), (-1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(-0.999), (-1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(-1.0), (-1, SubpixelBin::Zero));
+    assert_eq!(SubpixelBin::new(-1.124), (-1, SubpixelBin::Zero));
+}