image/math/
utils.rs

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1//! Shared mathematical utility functions.
2
3use std::cmp::max;
4
5/// Calculates the width and height an image should be resized to.
6/// This preserves aspect ratio, and based on the `fill` parameter
7/// will either fill the dimensions to fit inside the smaller constraint
8/// (will overflow the specified bounds on one axis to preserve
9/// aspect ratio), or will shrink so that both dimensions are
10/// completely contained within the given `width` and `height`,
11/// with empty space on one axis.
12pub(crate) fn resize_dimensions(
13    width: u32,
14    height: u32,
15    nwidth: u32,
16    nheight: u32,
17    fill: bool,
18) -> (u32, u32) {
19    let wratio = f64::from(nwidth) / f64::from(width);
20    let hratio = f64::from(nheight) / f64::from(height);
21
22    let ratio = if fill {
23        f64::max(wratio, hratio)
24    } else {
25        f64::min(wratio, hratio)
26    };
27
28    let nw = max((f64::from(width) * ratio).round() as u64, 1);
29    let nh = max((f64::from(height) * ratio).round() as u64, 1);
30
31    if nw > u64::from(u32::MAX) {
32        let ratio = f64::from(u32::MAX) / f64::from(width);
33        (u32::MAX, max((f64::from(height) * ratio).round() as u32, 1))
34    } else if nh > u64::from(u32::MAX) {
35        let ratio = f64::from(u32::MAX) / f64::from(height);
36        (max((f64::from(width) * ratio).round() as u32, 1), u32::MAX)
37    } else {
38        (nw as u32, nh as u32)
39    }
40}
41
42#[cfg(test)]
43mod test {
44    quickcheck! {
45        fn resize_bounds_correctly_width(old_w: u32, new_w: u32) -> bool {
46            if old_w == 0 || new_w == 0 { return true; }
47            // In this case, the scaling is limited by scaling of height.
48            // We could check that case separately but it does not conform to the same expectation.
49            if u64::from(new_w) * 400u64 >= u64::from(old_w) * u64::from(u32::MAX) { return true; }
50
51            let result = super::resize_dimensions(old_w, 400, new_w, u32::MAX, false);
52            let exact = (400_f64 * f64::from(new_w) / f64::from(old_w)).round() as u32;
53            result.0 == new_w && result.1 == exact.max(1)
54        }
55    }
56
57    quickcheck! {
58        fn resize_bounds_correctly_height(old_h: u32, new_h: u32) -> bool {
59            if old_h == 0 || new_h == 0 { return true; }
60            // In this case, the scaling is limited by scaling of width.
61            // We could check that case separately but it does not conform to the same expectation.
62            if 400u64 * u64::from(new_h) >= u64::from(old_h) * u64::from(u32::MAX) { return true; }
63
64            let result = super::resize_dimensions(400, old_h, u32::MAX, new_h, false);
65            let exact = (400_f64 * f64::from(new_h) / f64::from(old_h)).round() as u32;
66            result.1 == new_h && result.0 == exact.max(1)
67        }
68    }
69
70    #[test]
71    fn resize_handles_fill() {
72        let result = super::resize_dimensions(100, 200, 200, 500, true);
73        assert!(result.0 == 250);
74        assert!(result.1 == 500);
75
76        let result = super::resize_dimensions(200, 100, 500, 200, true);
77        assert!(result.0 == 500);
78        assert!(result.1 == 250);
79    }
80
81    #[test]
82    fn resize_never_rounds_to_zero() {
83        let result = super::resize_dimensions(1, 150, 128, 128, false);
84        assert!(result.0 > 0);
85        assert!(result.1 > 0);
86    }
87
88    #[test]
89    fn resize_handles_overflow() {
90        let result = super::resize_dimensions(100, u32::MAX, 200, u32::MAX, true);
91        assert!(result.0 == 100);
92        assert!(result.1 == u32::MAX);
93
94        let result = super::resize_dimensions(u32::MAX, 100, u32::MAX, 200, true);
95        assert!(result.0 == u32::MAX);
96        assert!(result.1 == 100);
97    }
98
99    #[test]
100    fn resize_rounds() {
101        // Only truncation will result in (3840, 2229) and (2160, 3719)
102        let result = super::resize_dimensions(4264, 2476, 3840, 2160, true);
103        assert_eq!(result, (3840, 2230));
104
105        let result = super::resize_dimensions(2476, 4264, 2160, 3840, false);
106        assert_eq!(result, (2160, 3720));
107    }
108
109    #[test]
110    fn resize_handles_zero() {
111        let result = super::resize_dimensions(0, 100, 100, 100, false);
112        assert_eq!(result, (1, 100));
113
114        let result = super::resize_dimensions(100, 0, 100, 100, false);
115        assert_eq!(result, (100, 1));
116
117        let result = super::resize_dimensions(100, 100, 0, 100, false);
118        assert_eq!(result, (1, 1));
119
120        let result = super::resize_dimensions(100, 100, 100, 0, false);
121        assert_eq!(result, (1, 1));
122    }
123}
image/math/utils.rs

image/math/
utils.rs
