physis/bcn/
bc3.rs

1// SPDX-FileCopyrightText: 2023 Rudolf Kolbe
2// SPDX-License-Identifier: MIT
3
4use super::bc1::decode_bc1_block;
5
6#[inline]
7pub fn decode_bc3_alpha(data: &[u8], outbuf: &mut [u32], channel: usize) {
8    // use u16 to avoid overflow and replicate equivalent behavior to C++ code
9    let mut a: [u16; 8] = [data[0] as u16, data[1] as u16, 0, 0, 0, 0, 0, 0];
10    if a[0] > a[1] {
11        a[2] = (a[0] * 6 + a[1]) / 7;
12        a[3] = (a[0] * 5 + a[1] * 2) / 7;
13        a[4] = (a[0] * 4 + a[1] * 3) / 7;
14        a[5] = (a[0] * 3 + a[1] * 4) / 7;
15        a[6] = (a[0] * 2 + a[1] * 5) / 7;
16        a[7] = (a[0] + a[1] * 6) / 7;
17    } else {
18        a[2] = (a[0] * 4 + a[1]) / 5;
19        a[3] = (a[0] * 3 + a[1] * 2) / 5;
20        a[4] = (a[0] * 2 + a[1] * 3) / 5;
21        a[5] = (a[0] + a[1] * 4) / 5;
22        a[6] = 0;
23        a[7] = 255;
24    }
25
26    let mut d: usize = (u64::from_le_bytes(data[..8].try_into().unwrap()) >> 16) as usize;
27
28    let channel_shift = channel * 8;
29    let channel_mask = 0xFFFFFFFF ^ (0xFF << channel_shift);
30    outbuf.iter_mut().for_each(|p| {
31        *p = (*p & channel_mask) | ((a[d & 7] as u32) << channel_shift);
32        d >>= 3;
33    });
34}
35
36#[inline]
37pub fn decode_bc3_block(data: &[u8], outbuf: &mut [u32]) {
38    decode_bc1_block(&data[8..], outbuf);
39    decode_bc3_alpha(data, outbuf, 3);
40}
physis/bcn/bc3.rs

physis/bcn/
bc3.rs
