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Fix: wrapping, store previous pixel value

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The wrapping wasn't working properly, clearly, but I forgot about the
previous pixel entirely.

I'll add some more explicit tests for the previous pixel behavior. I
think it's still broken for RGB and RGBA, because I'm dumb.
This commit is contained in:
Robert Garrett
2024-05-07 09:48:35 -05:00
parent 62b35b5aba
commit b05daa503e
1 changed files with 22 additions and 18 deletions
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40
src/main.rs
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@@ -134,29 +134,33 @@ where
return Some(self.back_buffer[idx]);
}
QOI_OP_DIFF => {
let dr = ((byte & 0b0011_0000) >> 4) - 2;
let dg = ((byte & 0b0000_1100) >> 2) - 2;
let db = (byte & 0b0000_0011) - 2;
return Some(PixelRGBA {
r: self.prev_pixel.r + dr,
g: self.prev_pixel.g + dg,
b: self.prev_pixel.b + db,
let dr = ((byte & 0b0011_0000) >> 4).wrapping_sub(2);
let dg = ((byte & 0b0000_1100) >> 2).wrapping_sub(2);
let db = (byte & 0b0000_0011).wrapping_sub(2);
let result = PixelRGBA {
r: self.prev_pixel.r.wrapping_add(dr),
g: self.prev_pixel.g.wrapping_add(dg),
b: self.prev_pixel.b.wrapping_add(db),
a: self.prev_pixel.a,
});
};
self.prev_pixel = result;
return Some(result);
}
QOI_OP_LUMA => {
let dg = (byte & !QOI_OP_SMALL_MASK) - 32;
let dg = (byte & !QOI_OP_SMALL_MASK).wrapping_sub(32);
let packed = self.bytes.next()?;
let drdg = ((packed & 0b1111_0000) >> 4) - 8;
let dbdg = (packed & 0b0000_1111) - 8;
let dr = drdg + dg;
let db = dbdg + dg;
return Some(PixelRGBA {
r: self.prev_pixel.r + dr,
g: self.prev_pixel.g + dg,
b: self.prev_pixel.b + db,
let drdg = ((packed & 0b1111_0000) >> 4).wrapping_sub(8);
let dbdg = (packed & 0b0000_1111).wrapping_sub(8);
let dr = drdg.wrapping_add(dg);
let db = dbdg.wrapping_add(dg);
let result = PixelRGBA {
r: self.prev_pixel.r.wrapping_add(dr),
g: self.prev_pixel.g.wrapping_add(dg),
b: self.prev_pixel.b.wrapping_add(db),
a: self.prev_pixel.a,
});
};
self.prev_pixel = result;
return Some(result);
}
QOI_OP_RUN => {
self.run_len = byte & !QOI_OP_SMALL_MASK;