read_fonts/tables/
cvar.rs

1//! The [cvar (CVT Variations)](https://learn.microsoft.com/en-us/typography/opentype/spec/cvar)
2//! table.
3
4include!("../../generated/generated_cvar.rs");
5
6use super::variations::{
7    PackedPointNumbers, TupleDelta, TupleVariationCount, TupleVariationData, TupleVariationHeader,
8};
9
10/// Variation data specialized for the CVT variation table.
11pub type CvtVariationData<'a> = TupleVariationData<'a, CvtDelta>;
12
13impl<'a> Cvar<'a> {
14    /// Returns the variation data containing the tuples and deltas for the
15    /// control value table.
16    ///
17    /// This table doesn't contain an axis count field so this must be provided
18    /// by the user and can be read from the `fvar` table.
19    pub fn variation_data(&self, axis_count: u16) -> Result<CvtVariationData<'a>, ReadError> {
20        let count = self.tuple_variation_count();
21        let data = self.data()?;
22        let header_data = self.raw_tuple_header_data();
23        // if there are shared point numbers, get them now
24        let (shared_point_numbers, serialized_data) = if count.shared_point_numbers() {
25            let (packed, data) = PackedPointNumbers::split_off_front(data);
26            (Some(packed), data)
27        } else {
28            (None, data)
29        };
30        Ok(CvtVariationData {
31            tuple_count: count,
32            axis_count,
33            shared_tuples: None,
34            shared_point_numbers,
35            header_data,
36            serialized_data,
37            _marker: std::marker::PhantomData,
38        })
39    }
40
41    /// Computes the accumulated deltas for the given set of normalized
42    /// coordinates and stores them in `deltas`.
43    ///
44    /// The `axis_count` parameter expects the value from the `fvar`
45    /// table.
46    ///
47    /// The `deltas` slice should have a length greater than or equal
48    /// to the number of values in the `cvt` table. The values are
49    /// computed in 16.16 format.
50    pub fn deltas(
51        &self,
52        axis_count: u16,
53        coords: &[F2Dot14],
54        deltas: &mut [i32],
55    ) -> Result<(), ReadError> {
56        let var_data = self.variation_data(axis_count)?;
57        for (tuple, scalar) in var_data.active_tuples_at(coords) {
58            for delta in tuple.deltas() {
59                let ix = delta.position as usize;
60                if let Some(value) = deltas.get_mut(ix) {
61                    *value += delta.apply_scalar(scalar).to_bits();
62                }
63            }
64        }
65        Ok(())
66    }
67
68    fn raw_tuple_header_data(&self) -> FontData<'a> {
69        let range = self.shape.tuple_variation_headers_byte_range();
70        self.data.split_off(range.start).unwrap()
71    }
72}
73
74/// Delta for an entry in the control value table.
75#[derive(Clone, Copy, Debug, PartialEq, Eq)]
76pub struct CvtDelta {
77    /// The index in the CVT.
78    pub position: u16,
79    /// The delta to apply to the value in the CVT.
80    pub value: i32,
81}
82
83impl CvtDelta {
84    /// Applies a tuple scalar to this delta.
85    pub fn apply_scalar(self, scalar: Fixed) -> Fixed {
86        Fixed::from_i32(self.value) * scalar
87    }
88}
89
90impl TupleDelta for CvtDelta {
91    fn is_point() -> bool {
92        false
93    }
94
95    fn new(position: u16, x: i32, _y: i32) -> Self {
96        Self { position, value: x }
97    }
98}
99
100#[cfg(test)]
101mod tests {
102    use font_types::F2Dot14;
103
104    use crate::{FontRef, TableProvider};
105
106    #[test]
107    fn scaled_deltas() {
108        let font = FontRef::new(font_test_data::CVAR).unwrap();
109        // Elements are ([coords], [deltas]) where deltas are fixed point
110        // values.
111        // These were generated by fancy printf debugging in FreeType.
112        let cases = &[
113            (
114                [0.5, 0.5],
115                [
116                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
117                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
118                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 720896, 3276800, 1179648, 0, 0, 0, 0, 0,
119                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 622592, 0, 1179648, 0, 0, 0, 0, 0, 622592,
120                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
121                ],
122            ),
123            (
124                [-0.5, 0.5],
125                [
126                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
127                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
128                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1441792, -2162688, -1277952, 0, 0, 0,
129                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -917504, 0, -1277952, 0, 0, 0, 0, 0,
130                    -720896, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
131                    0, 0, 0,
132                ],
133            ),
134            (
135                [0.5, -0.5],
136                [
137                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
138                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
139                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1900544, 2621440, 2129920, 0, 0, 0, 0,
140                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 360448, 0, 1015808, 0, 0, 0, 0, 0,
141                    524288, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
142                    0, 0,
143                ],
144            ),
145            (
146                [-0.5, -0.5],
147                [
148                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
149                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
150                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1212416, -2293760, -1130496, 0, 0, 0,
151                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1097728, 0, -1277952, 0, 0, 0, 0, 0,
152                    -737280, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
153                    0, 0, 0,
154                ],
155            ),
156            (
157                [-1.0, -1.0],
158                [
159                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
160                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
161                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2490368, -4325376, -2490368, 0, 0, 0,
162                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1835008, 0, -2555904, 0, 0, 0, 0, 0,
163                    -1441792, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
164                    0, 0, 0,
165                ],
166            ),
167            (
168                [1.0, 1.0],
169                [
170                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
171                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
172                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1441792, 6553600, 2359296, 0, 0, 0, 0,
173                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1245184, 0, 2359296, 0, 0, 0, 0, 0,
174                    1245184, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
175                    0, 0, 0,
176                ],
177            ),
178            (
179                [-1.0, 1.0],
180                [
181                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
182                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
183                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -2883584, -4325376, -2555904, 0, 0, 0,
184                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1835008, 0, -2555904, 0, 0, 0, 0, 0,
185                    -1441792, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
186                    0, 0, 0,
187                ],
188            ),
189            (
190                [1.0, -1.0],
191                [
192                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
193                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
194                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5636096, 4456448, 5636096, 0, 0, 0, 0,
195                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 917504, 0, 1703936, 0, 0, 0, 0, 0,
196                    917504, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
197                    0, 0,
198                ],
199            ),
200        ];
201        let cvar = font.cvar().unwrap();
202        let axis_count = font.fvar().unwrap().axis_count();
203        let cvar_data = cvar.variation_data(axis_count).unwrap();
204        for (coords, expected_deltas) in cases {
205            let coords = coords.map(F2Dot14::from_f32);
206            let mut deltas = vec![0; expected_deltas.len()];
207            for tuple in cvar_data.tuples() {
208                let Some(scalar) = tuple.compute_scalar(&coords) else {
209                    continue;
210                };
211                for delta in tuple.deltas() {
212                    let scaled_delta = delta.apply_scalar(scalar);
213                    deltas[delta.position as usize] += scaled_delta.to_bits();
214                }
215            }
216            assert_eq!(&deltas, expected_deltas);
217        }
218    }
219
220    #[test]
221    fn raw_tuple_deltas() {
222        let font = FontRef::new(font_test_data::CVAR).unwrap();
223        let cvar = font.cvar().unwrap();
224        let axis_count = font.fvar().unwrap().axis_count();
225        let cvar_data = cvar.variation_data(axis_count).unwrap();
226        // An array of slices of (point number, delta) pairs, one for each
227        // tuple.
228        // These were taken directly from the ttx
229        let expected = [
230            &[(65, 8), (66, -8), (67, 8), (85, -11), (87, 0), (93, -1)],
231            &[(65, -2), (66, 8), (67, -7), (85, 11), (87, 0), (93, 1)],
232            &[(65, 56), (66, -24), (67, 42), (85, 6), (87, -10), (93, -4)],
233            &[
234                (65, -44),
235                (66, -66),
236                (67, -39),
237                (85, -28),
238                (87, -39),
239                (93, -22),
240            ],
241            &[(65, 22), (66, 100), (67, 36), (85, 19), (87, 36), (93, 19)],
242            &[(65, 8), (66, 0), (67, 8), (85, -43), (87, -49), (93, -32)],
243            &[(65, -8), (66, 0), (67, -8), (85, 11), (87, 9), (93, 1)],
244            &[(65, -80), (66, 0), (67, -90), (85, -6), (87, -47), (93, 4)],
245            &[(65, -16), (66, 0), (67, -21), (85, 28), (87, 39), (93, 22)],
246            &[
247                (65, -46),
248                (66, 0),
249                (67, -22),
250                (85, -19),
251                (87, 35),
252                (93, -19),
253            ],
254            &[(65, 2), (66, 0), (67, 7), (85, -11), (87, -9), (93, -1)],
255        ];
256        let mut count = 0;
257        for (tuple, expected) in cvar_data.tuples().zip(&expected) {
258            count += 1;
259            let deltas = tuple
260                .deltas()
261                .map(|delta| (delta.position, delta.value))
262                .collect::<Vec<_>>();
263            assert_eq!(&deltas, expected);
264        }
265        assert_eq!(count, expected.len());
266    }
267}
read_fonts/tables/cvar.rs

read_fonts/tables/
cvar.rs
