1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
use crate::Blend;
use pix::{
Alpha, AlphaMode, AssocRgb, Channel, Format, GammaMode, Rgb, Translucent,
};
impl<C, A, M, G> Blend for Rgb<C, A, M, G>
where
C: Channel,
A: Alpha<Chan = C>,
A: From<C>,
M: AlphaMode,
G: GammaMode,
{
fn over_fallback<B, H>(dst: &mut [Self], src: &[B], clr: Self)
where
B: Format<Chan = H>,
C: From<H>,
H: Channel,
H: From<C>,
{
let clr: AssocRgb<H, Translucent<H>, G> = clr.convert();
for (bot, top) in dst.iter_mut().zip(src) {
let src: AssocRgb<H, Translucent<H>, G> = top.convert();
let src = clr * src;
*bot = Self::over(*bot, src);
}
}
fn over<B, H>(dst: Self, src: B) -> Self
where
B: Format<Chan = H>,
C: From<H>,
H: Channel,
H: From<C>,
{
let dst: AssocRgb<H, Translucent<H>, G> = dst.convert();
let src: AssocRgb<H, Translucent<H>, G> = src.convert();
let one_minus_src_a = H::MAX - src.alpha().value();
let a = src.alpha().value() + dst.alpha().value() * one_minus_src_a;
let r = src.red() + dst.red() * one_minus_src_a;
let g = src.green() + dst.green() * one_minus_src_a;
let b = src.blue() + dst.blue() * one_minus_src_a;
AssocRgb::<C, Translucent<C>, G>::with_alpha(r, g, b, a).convert()
}
}
#[cfg(test)]
mod tests {
use super::Blend;
#[test]
fn rgba8_transparent() {
let t = pix::AssocSRgba8::with_alpha(0x00, 0x00, 0x00, 0x00);
let p = pix::AssocSRgba8::with_alpha(20, 40, 80, 160);
let r1 = Blend::over(t, p);
let r2 = Blend::over(p, t);
assert_eq!(r1, p);
assert_eq!(r1, r2);
}
#[test]
fn transparent_over_white() {
let t = pix::AssocSRgba8::with_alpha(0x00, 0x00, 0x00, 0x00);
let p = pix::AssocSRgba8::new(0xFF, 0xFF, 0xFF);
let r = Blend::over(p, t);
assert_eq!(r, p);
}
}