tiny_skia/
fixed_point.rs

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1// Copyright 2006 The Android Open Source Project
2// Copyright 2020 Yevhenii Reizner
3//
4// Use of this source code is governed by a BSD-style license that can be
5// found in the LICENSE file.
6
7// Skia uses fixed points pretty chaotically, therefore we cannot use
8// strongly typed wrappers. Which is unfortunate.
9
10use tiny_skia_path::SaturateCast;
11
12use crate::math::{bound, left_shift, left_shift64};
13
14/// A 26.6 fixed point.
15pub type FDot6 = i32;
16
17/// A 24.8 fixed point.
18pub type FDot8 = i32;
19
20/// A 16.16 fixed point.
21pub type FDot16 = i32;
22
23pub mod fdot6 {
24    use super::*;
25    use core::convert::TryFrom;
26
27    pub const ONE: FDot6 = 64;
28
29    pub fn from_i32(n: i32) -> FDot6 {
30        debug_assert!(n as i16 as i32 == n);
31        n << 6
32    }
33
34    pub fn from_f32(n: f32) -> FDot6 {
35        (n * 64.0) as i32
36    }
37
38    pub fn floor(n: FDot6) -> FDot6 {
39        n >> 6
40    }
41
42    pub fn ceil(n: FDot6) -> FDot6 {
43        (n + 63) >> 6
44    }
45
46    pub fn round(n: FDot6) -> FDot6 {
47        (n + 32) >> 6
48    }
49
50    pub fn to_fdot16(n: FDot6) -> FDot16 {
51        debug_assert!((left_shift(n, 10) >> 10) == n);
52        left_shift(n, 10)
53    }
54
55    pub fn div(a: FDot6, b: FDot6) -> FDot16 {
56        debug_assert_ne!(b, 0);
57
58        if i16::try_from(a).is_ok() {
59            left_shift(a, 16) / b
60        } else {
61            fdot16::div(a, b)
62        }
63    }
64
65    pub fn can_convert_to_fdot16(n: FDot6) -> bool {
66        let max_dot6 = i32::MAX >> (16 - 6);
67        n.abs() <= max_dot6
68    }
69
70    pub fn small_scale(value: u8, dot6: FDot6) -> u8 {
71        debug_assert!(dot6 as u32 <= 64);
72        ((value as i32 * dot6) >> 6) as u8
73    }
74}
75
76pub mod fdot8 {
77    use super::*;
78
79    // Extracted from SkScan_Antihair.cpp
80
81    pub fn from_fdot16(x: FDot16) -> FDot8 {
82        (x + 0x80) >> 8
83    }
84}
85
86pub mod fdot16 {
87    use super::*;
88
89    pub const HALF: FDot16 = (1 << 16) / 2;
90    pub const ONE: FDot16 = 1 << 16;
91
92    // `from_f32` seems to lack a rounding step. For all fixed-point
93    // values, this version is as accurate as possible for (fixed -> float -> fixed). Rounding reduces
94    // accuracy if the intermediate floats are in the range that only holds integers (adding 0.5 to an
95    // odd integer then snaps to nearest even). Using double for the rounding math gives maximum
96    // accuracy for (float -> fixed -> float), but that's usually overkill.
97    pub fn from_f32(x: f32) -> FDot16 {
98        i32::saturate_from(x * ONE as f32)
99    }
100
101    pub fn floor_to_i32(x: FDot16) -> i32 {
102        x >> 16
103    }
104
105    pub fn ceil_to_i32(x: FDot16) -> i32 {
106        (x + ONE - 1) >> 16
107    }
108
109    pub fn round_to_i32(x: FDot16) -> i32 {
110        (x + HALF) >> 16
111    }
112
113    // The divide may exceed 32 bits. Clamp to a signed 32 bit result.
114    pub fn mul(a: FDot16, b: FDot16) -> FDot16 {
115        ((i64::from(a) * i64::from(b)) >> 16) as FDot16
116    }
117
118    // The divide may exceed 32 bits. Clamp to a signed 32 bit result.
119    pub fn div(numer: FDot6, denom: FDot6) -> FDot16 {
120        let v = left_shift64(numer as i64, 16) / denom as i64;
121        let n = bound(i32::MIN as i64, v, i32::MAX as i64);
122        n as i32
123    }
124
125    pub fn fast_div(a: FDot6, b: FDot6) -> FDot16 {
126        debug_assert!((left_shift(a, 16) >> 16) == a);
127        debug_assert!(b != 0);
128        left_shift(a, 16) / b
129    }
130}
tiny_skia/fixed_point.rs

tiny_skia/
fixed_point.rs
