blekin/crates/ericrfb/src/codec/hextile.rs

use std::io::Read;

use crate::framebuffer::Framebuffer;
use crate::proto::{self, read_exact, read_u8};

// Subencoding flag bits — ByteColorRFBRenderer.int(), line 192
const RAW: u8 = 1;
const BACKGROUND_SPECIFIED: u8 = 2;
const FOREGROUND_SPECIFIED: u8 = 4;
const ANY_SUBRECTS: u8 = 8;
const SUBRECTS_COLOURED: u8 = 16;

/// Decode a Hextile-encoded rectangle into the framebuffer.
///
/// The rectangle is divided into 16x16 tiles (edge tiles may be smaller).
/// Background and foreground colors persist across tiles within one call.
///
/// Reference: ByteColorRFBRenderer.int() line 169.
pub fn decode_hextile(
    r: &mut impl Read,
    fb: &mut Framebuffer,
    rx: u16,
    ry: u16,
    rw: u16,
    rh: u16,
) -> proto::Result<()> {
    let mut bg: u8 = 0;
    let mut fg: u8 = 0;

    let mut ty = ry;
    while ty < ry + rh {
        let tile_h = (ry + rh - ty).min(16);
        let mut tx = rx;
        while tx < rx + rw {
            let tile_w = (rx + rw - tx).min(16);
            let flags = read_u8(r)?;

            if flags & RAW != 0 {
                // Raw tile: read tile_w * tile_h bytes
                let size = tile_w as usize * tile_h as usize;
                let data = read_exact(r, size)?;
                fb.apply_raw(tx, ty, tile_w, tile_h, &data);
                tx += 16;
                continue;
            }

            if flags & BACKGROUND_SPECIFIED != 0 {
                bg = read_u8(r)?;
            }

            // Fill tile with background
            fb.fill_rect(tx, ty, tile_w, tile_h, bg);

            if flags & FOREGROUND_SPECIFIED != 0 {
                fg = read_u8(r)?;
            }

            if flags & ANY_SUBRECTS != 0 {
                let num_subrects = read_u8(r)?;
                let coloured = flags & SUBRECTS_COLOURED != 0;

                for _ in 0..num_subrects {
                    let color = if coloured { read_u8(r)? } else { fg };
                    let xy = read_u8(r)?;
                    let wh = read_u8(r)?;
                    let sx = (xy >> 4) as u16;
                    let sy = (xy & 0x0F) as u16;
                    let sw = ((wh >> 4) + 1) as u16;
                    let sh = ((wh & 0x0F) + 1) as u16;
                    fb.fill_rect(tx + sx, ty + sy, sw, sh, color);
                }
            }

            tx += 16;
        }
        ty += 16;
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::Cursor;

    #[test]
    fn test_hextile_raw_tile() {
        let mut fb = Framebuffer::new(16, 16);
        // One 16x16 tile, Raw subencoding
        let mut data = vec![RAW]; // flags
        data.extend_from_slice(&[0x42u8; 256]); // 16*16 raw pixels
        let mut c = Cursor::new(data);
        decode_hextile(&mut c, &mut fb, 0, 0, 16, 16).unwrap();
        assert_eq!(fb.pixels[0], 0x42);
        assert_eq!(fb.pixels[255], 0x42);
    }

    #[test]
    fn test_hextile_bg_fill() {
        let mut fb = Framebuffer::new(16, 16);
        // One tile: background=0x09, no subrects
        let data = vec![BACKGROUND_SPECIFIED, 0x09];
        let mut c = Cursor::new(data);
        decode_hextile(&mut c, &mut fb, 0, 0, 16, 16).unwrap();
        assert!(fb.pixels.iter().all(|&p| p == 0x09));
    }

    #[test]
    fn test_hextile_subrects_coloured() {
        let mut fb = Framebuffer::new(16, 16);
        // Background=0x00, 1 coloured subrect at (2,3) size 4x5 color 0xFF
        let data = vec![
            BACKGROUND_SPECIFIED | ANY_SUBRECTS | SUBRECTS_COLOURED,
            0x00, // bg
            1,    // num_subrects
            0xFF, // subrect color
            0x23, // xy: x=2, y=3
            0x34, // wh: w=3+1=4, h=4+1=5
        ];
        let mut c = Cursor::new(data);
        decode_hextile(&mut c, &mut fb, 0, 0, 16, 16).unwrap();
        assert_eq!(fb.pixels[0], 0x00); // background
        assert_eq!(fb.pixels[3 * 16 + 2], 0xFF); // subrect at (2,3)
        assert_eq!(fb.pixels[7 * 16 + 5], 0xFF); // subrect at (5,7)
        assert_eq!(fb.pixels[8 * 16 + 2], 0x00); // below subrect
    }

    #[test]
    fn test_hextile_fg_subrects() {
        let mut fb = Framebuffer::new(16, 16);
        // Background=0x00, foreground=0xAA, 1 subrect at (0,0) size 2x2
        let data = vec![
            BACKGROUND_SPECIFIED | FOREGROUND_SPECIFIED | ANY_SUBRECTS,
            0x00, // bg
            0xAA, // fg
            1,    // num_subrects
            0x00, // xy: x=0, y=0
            0x11, // wh: w=1+1=2, h=1+1=2
        ];
        let mut c = Cursor::new(data);
        decode_hextile(&mut c, &mut fb, 0, 0, 16, 16).unwrap();
        assert_eq!(fb.pixels[0], 0xAA);
        assert_eq!(fb.pixels[1], 0xAA);
        assert_eq!(fb.pixels[16], 0xAA);
        assert_eq!(fb.pixels[17], 0xAA);
        assert_eq!(fb.pixels[2], 0x00);
    }
}