Add the ability to parse Fontra components

fontra2fontir/Cargo.toml

@@ -16,8 +16,6 @@ fontir = { version = "0.0.1", path = "../fontir" }
 
 write-fonts.workspace = true
 
-percent-encoding = "2.3.1"
-
 log.workspace = true
 env_logger.workspace = true
 

fontra2fontir/src/fontra.rs

@@ -3,21 +3,105 @@
 //! See <https://github.com/googlefonts/fontra/blob/main/src/fontra/core/classes.py>
 
 use std::{
-    collections::HashMap,
+    collections::{BTreeMap, HashMap},
     fs,
     path::{Path, PathBuf},
 };
 
 use fontdrasil::types::GlyphName;
 use fontir::error::Error;
-use percent_encoding::{utf8_percent_encode, NON_ALPHANUMERIC};
 use serde::Deserialize;
 use write_fonts::types::Tag;
 
+const SEPARATOR_CHAR: char = '^';
+
+fn is_reserved_char(c: char) -> bool {
+    let c = c as u32;
+    match c {
+        _ if c < 32 => true,
+        _ if c == 0x7F => true,
+        _ if c == SEPARATOR_CHAR as u32 => true,
+        _ => false,
+    }
+}
+
+fn is_reserved_filename(name: &str) -> bool {
+    matches!(
+        name.to_ascii_uppercase().as_str(),
+        "CON"
+            | "PRN"
+            | "AUX"
+            | "CLOCK$"
+            | "NUL"
+            | "COM1"
+            | "LPT1"
+            | "LPT2"
+            | "LPT3"
+            | "COM2"
+            | "COM3"
+            | "COM4"
+    )
+}
+
+const BASE_32_CHARS: [char; 32] = [
+    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I',
+    'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
+];
+
+/// Matches <https://github.com/googlefonts/fontra/blob/15bc0b8401054390484cfb86d509d633d29657a1/src/fontra/backends/filenames.py#L40-L64>
+fn string_to_filename(string: &str, suffix: &str) -> String {
+    let mut code_digits: Vec<_> = (0..string.len())
+        .step_by(5)
+        .map(|i| {
+            let mut digit = 0;
+            let mut bit = 1;
+            for c in string[i..(i + 5).min(string.len())].chars() {
+                if c.is_ascii_uppercase() {
+                    digit |= bit
+                }
+                bit <<= 1;
+            }
+            digit
+        })
+        .collect();
+    while let Some(0) = code_digits.last() {
+        code_digits.pop();
+    }
+
+    let mut filename = Vec::new();
+    for (i, c) in string.chars().enumerate() {
+        if i == 0 && c == '.' {
+            filename.extend("%2E".chars());
+        } else if !is_reserved_char(c) {
+            filename.push(c);
+        } else {
+            let c = c as u32;
+            for c in format!("{c:02X}").chars() {
+                filename.push(c);
+            }
+        }
+    }
+
+    if code_digits.is_empty() && is_reserved_filename(string) {
+        code_digits.push(0);
+    }
+
+    if !code_digits.is_empty() {
+        filename.push(SEPARATOR_CHAR);
+        for d in code_digits {
+            assert!(d < 32, "We've made a terrible mistake");
+            filename.push(BASE_32_CHARS[d]);
+        }
+    }
+
+    for c in suffix.chars() {
+        filename.push(c);
+    }
+    filename.into_iter().collect()
+}
+
 pub(crate) fn glyph_file(glyph_dir: &Path, glyph: GlyphName) -> PathBuf {
-    // TODO(https://github.com/googlefonts/fontc/issues/688): fontra string => filename algorithm
-    let filename = utf8_percent_encode(glyph.as_str(), NON_ALPHANUMERIC);
-    glyph_dir.join(filename.to_string() + ".json")
+    glyph_dir.join(string_to_filename(glyph.as_str(), ".json"))
 }
 
 fn from_file<T>(p: &Path) -> Result<T, Error>
@@ -66,8 +150,26 @@ pub(crate) struct FontraAxis {
 #[allow(dead_code)] // TEMPORARY
 pub(crate) struct FontraGlyph {
     pub(crate) name: GlyphName,
+    /// Variable component, or glyph-local, axes
+    #[serde(default)]
+    pub(crate) axes: Vec<FontraGlyphAxis>,
     pub(crate) sources: Vec<FontraSource>,
-    pub(crate) layers: HashMap<String, FontraLayer>,
+    pub(crate) layers: BTreeMap<String, FontraLayer>,
+}
+
+/// An axis specific to a glyph meant to be used as a variable component
+///
+/// <https://github.com/googlefonts/fontra/blob/15bc0b8401054390484cfb86d509d633d29657a1/src/fontra/core/classes.py#L96-L101>
+#[derive(Debug, Clone, Deserialize)]
+#[allow(dead_code)] // TEMPORARY
+pub(crate) struct FontraGlyphAxis {
+    pub(crate) name: String,
+    #[serde(rename = "minValue")]
+    pub(crate) min_value: f64,
+    #[serde(rename = "defaultValue")]
+    pub(crate) default_value: f64,
+    #[serde(rename = "maxValue")]
+    pub(crate) max_value: f64,
 }
 
 /// <https://github.com/googlefonts/fontra/blob/a4edd06837118e583804fd963c22ed806a315b04/src/fontra/core/classes.py#L119-L126>
@@ -78,7 +180,7 @@ pub(crate) struct FontraSource {
     #[serde(rename = "layerName")]
     pub(crate) layer_name: String,
     #[serde(default)]
-    pub(crate) location: HashMap<Tag, f64>,
+    pub(crate) location: HashMap<String, f64>,
     // TODO: locationBase
     #[serde(default)]
     pub(crate) inactive: bool,
@@ -100,6 +202,8 @@ pub(crate) struct FontraGlyphInstance {
     // TODO: Fontra has two representations, packed and unpacked. This only covers one.
     #[serde(default)]
     pub(crate) path: FontraPath,
+    #[serde(default)]
+    pub(crate) components: Vec<FontraComponent>,
 }
 
 impl FontraGlyph {
@@ -113,6 +217,7 @@ impl FontraGlyph {
 #[derive(Default, Debug, Clone, Deserialize)]
 #[allow(dead_code)] // TEMPORARY
 pub(crate) struct FontraPath {
+    #[serde(default)]
     pub(crate) contours: Vec<FontraContour>,
 }
 
@@ -173,6 +278,51 @@ impl PointType {
     }
 }
 
+/// <https://github.com/googlefonts/fontra/blob/a4edd06837118e583804fd963c22ed806a315b04/src/fontra/core/classes.py#L154-L158>
+#[derive(Debug, Clone, Deserialize)]
+#[allow(dead_code)] // TEMPORARY
+pub(crate) struct FontraComponent {
+    pub(crate) name: GlyphName,
+    #[serde(default)]
+    pub(crate) transformation: FontraTransform,
+    // This location is in terms of axes defined by the referenced glyph
+    #[serde(default)]
+    pub(crate) location: HashMap<String, f64>,
+}
+
+/// What FontTools calls a DecomposedTransform
+///
+/// <https://github.com/fonttools/fonttools/blob/0572f7871823bdef3ceceaf41dedd0a6bd100995/Lib/fontTools/misc/transform.py#L410-L424>
+#[derive(Default, Debug, Clone, Deserialize)]
+#[allow(dead_code)] // TEMPORARY
+pub(crate) struct FontraTransform {
+    #[serde(rename = "translateX", default)]
+    translate_x: f64,
+    #[serde(rename = "translateY", default)]
+    translate_y: f64,
+    /// in degrees counter-clockwise in font coordinate space
+    #[serde(default)]
+    rotation: f64,
+    #[serde(rename = "scaleX", default = "float_one")]
+    scale_x: f64,
+    #[serde(rename = "scaleY", default = "float_one")]
+    scale_y: f64,
+    /// in degrees clockwise in font coordinate space
+    #[serde(rename = "skewX", default)]
+    skew_x: f64,
+    /// in degrees counter-clockwise in font coordinate space
+    #[serde(rename = "skewY", default)]
+    skew_y: f64,
+    #[serde(rename = "tCenterX", default)]
+    t_center_x: f64,
+    #[serde(rename = "tCenterY", default)]
+    t_center_y: f64,
+}
+
+fn float_one() -> f64 {
+    1.0
+}
+
 #[cfg(test)]
 mod tests {
     use std::collections::HashSet;
@@ -200,6 +350,22 @@ mod tests {
             .collect::<Vec<_>>()
     }
 
+    fn glyph_axis_tuples(glyph: &FontraGlyph) -> Vec<(&str, f64, f64, f64)> {
+        glyph
+            .axes
+            .iter()
+            .map(|a| (a.name.as_str(), a.min_value, a.default_value, a.max_value))
+            .collect::<Vec<_>>()
+    }
+
+    fn read_test_glyph(fontra_dir: &str, glyph_name: &str) -> FontraGlyph {
+        let file = testdata_dir()
+            .join(fontra_dir)
+            .join("glyphs")
+            .join(string_to_filename(glyph_name, ".json"));
+        FontraGlyph::from_file(&file).unwrap_or_else(|e| panic!("Unable to read {file:?}: {e}"))
+    }
+
     #[test]
     fn fontdata_of_minimal() {
         let font_data =
@@ -238,9 +404,7 @@ mod tests {
 
     #[test]
     fn read_notdef() {
-        let glyph =
-            FontraGlyph::from_file(&testdata_dir().join("minimal.fontra/glyphs/%2Enotdef.json"))
-                .unwrap();
+        let glyph = read_test_glyph("minimal.fontra", ".notdef");
         assert_eq!(GlyphName::new(".notdef"), glyph.name, "{glyph:#?}");
         assert_eq!(
             1000.0, glyph.layers["foreground"].glyph.x_advance,
@@ -249,10 +413,24 @@ mod tests {
     }
 
     #[test]
-    fn read_u20089() {
-        let glyph =
-            FontraGlyph::from_file(&testdata_dir().join("2glyphs.fontra/glyphs/u20089.json"))
-                .unwrap();
+    fn read_varc_axes() {
+        let glyph = read_test_glyph("component.fontra", "VG_4E00_00");
+        assert_eq!(
+            vec![
+                ("width", 200.0, 1000.0, 1000.0),
+                ("weight", 10.0, 33.0, 50.0),
+                ("serif_height", -50.0, 0.0, 100.0),
+                ("serif_width", -100.0, 0.0, 100.0),
+                ("serif_top_moveH", -50.0, 0.0, 50.0),
+                ("H_L_length", -800.0, 0.0, 800.0),
+            ],
+            glyph_axis_tuples(&glyph),
+        )
+    }
+
+    #[test]
+    fn read_simple_contours() {
+        let glyph = read_test_glyph("2glyphs.fontra", "u20089");
         assert_eq!(GlyphName::new("u20089"), glyph.name, "{glyph:#?}");
         let mut layer_names: Vec<_> = glyph.layers.keys().map(|n| n.as_str()).collect();
         layer_names.sort();
@@ -278,4 +456,46 @@ mod tests {
             contour.points[2].point_type().unwrap()
         );
     }
+
+    #[test]
+    fn read_simple_component() {
+        let glyph = read_test_glyph("component.fontra", "uni4E00");
+        assert_eq!(GlyphName::new("uni4E00"), glyph.name, "{glyph:#?}");
+        assert_eq!(
+            vec![
+                ("foreground".to_string(), GlyphName::new("VG_4E00_00")),
+                ("wght=1".to_string(), GlyphName::new("VG_4E00_00"))
+            ],
+            glyph
+                .layers
+                .iter()
+                .flat_map(|(n, l)| l
+                    .glyph
+                    .components
+                    .iter()
+                    .map(|c| (n.clone(), c.name.clone())))
+                .collect::<Vec<_>>(),
+        );
+    }
+
+    #[test]
+    fn match_python_string_to_filename() {
+        // expected is as observed in Python with .json appended
+        let exemplars = vec![
+            ("AUX", "AUX^7.json"),
+            (".notdef", "%2Enotdef.json"),
+            ("4E00", "4E00^2.json"),
+            ("VG_4E00_01", "VG_4E00_01^J.json"),
+        ];
+        let mut errors = Vec::new();
+        for (input, expected) in exemplars {
+            let actual = string_to_filename(input, ".json");
+            if expected != actual {
+                errors.push(format!(
+                    "\"{input}\" should convert to \"{expected}\" not \"{actual}\""
+                ));
+            }
+        }
+        assert_eq!(0, errors.len(), "{errors:#?}");
+    }
 }