game-toolkit-dosvideo 0.3.0

DOS-era PC graphics and sound for game-toolkit: VGA, Mode X, EGA, CGA, Hercules, Tandy and VESA SVGA at the register level, a beam-accurate CRT, a CRT shader and the PC speaker
Documentation 
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

//! A tiny dependency-free PNG encoder (stored deflate blocks), for screenshots.

fn crc32(data: &[u8], mut crc: u32) -> u32 {
    for &b in data {
        crc ^= b as u32;
        for _ in 0..8 {
            crc = if crc & 1 != 0 {
                0xEDB8_8320 ^ (crc >> 1)
            } else {
                crc >> 1
            };
        }
    }
    crc
}

fn chunk(out: &mut Vec<u8>, kind: &[u8; 4], data: &[u8]) {
    out.extend_from_slice(&(data.len() as u32).to_be_bytes());
    out.extend_from_slice(kind);
    out.extend_from_slice(data);
    let c = crc32(data, crc32(kind, 0xFFFF_FFFF)) ^ 0xFFFF_FFFF;
    out.extend_from_slice(&c.to_be_bytes());
}

/// Encode RGBA8 pixels as a PNG file.
pub fn encode_rgba(width: u32, height: u32, rgba: &[u8]) -> Vec<u8> {
    let mut raw = Vec::with_capacity((width as usize * 4 + 1) * height as usize);
    for row in rgba.chunks_exact(width as usize * 4).take(height as usize) {
        raw.push(0);
        raw.extend_from_slice(row);
    }
    let mut z = vec![0x78, 0x01];
    let mut blocks = raw.chunks(65535).peekable();
    if blocks.peek().is_none() {
        z.extend_from_slice(&[1, 0, 0, 0xFF, 0xFF]);
    }
    while let Some(b) = blocks.next() {
        z.push(u8::from(blocks.peek().is_none()));
        let n = b.len() as u16;
        z.extend_from_slice(&n.to_le_bytes());
        z.extend_from_slice(&(!n).to_le_bytes());
        z.extend_from_slice(b);
    }
    let (mut a, mut bb) = (1u32, 0u32);
    for &x in &raw {
        a = (a + x as u32) % 65521;
        bb = (bb + a) % 65521;
    }
    z.extend_from_slice(&((bb << 16) | a).to_be_bytes());
    let mut out = b"\x89PNG\r\n\x1a\n".to_vec();
    let mut ihdr = Vec::with_capacity(13);
    ihdr.extend_from_slice(&width.to_be_bytes());
    ihdr.extend_from_slice(&height.to_be_bytes());
    ihdr.extend_from_slice(&[8, 6, 0, 0, 0]);
    chunk(&mut out, b"IHDR", &ihdr);
    chunk(&mut out, b"IDAT", &z);
    chunk(&mut out, b"IEND", &[]);
    out
}

impl crate::crt::FrameView<'_> {
    /// The frame as a PNG file.
    pub fn to_png(&self) -> Vec<u8> {
        encode_rgba(self.width, self.height, self.rgba)
    }
}