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lzw encoding/decoding now reads/writes the min_code_size byte

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as such, lzw_decode now no longer needs min_code_size as a function
parameter since it just reads it from the source bytes
This commit is contained in:
Gered 2022-12-30 11:47:13 -05:00
parent 803b31d8c8
commit 88f8cbe1ad
2 changed files with 17 additions and 10 deletions
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6
libretrogd/src/graphics/bitmap/gif.rs
View file

@ -366,10 +366,9 @@ fn load_image_section<T: ReadBytesExt>(
palette = None; // we expect to find a local color table later
}
let lzw_minimum_code_size = reader.read_u8()?;
let mut bitmap = Bitmap::new(gif_header.screen_width as u32, gif_header.screen_height as u32).unwrap();
let mut writer = bitmap.pixels_mut();
lzw_decode(reader, &mut writer, lzw_minimum_code_size as usize)?;
lzw_decode(reader, &mut writer)?;
Ok((bitmap, palette))
}
@ -388,8 +387,9 @@ fn save_image_section<T: WriteBytesExt>(
};
image_descriptor.write(writer)?;
// todo: allow this to changed based on the input palette, if/when we allow gifs to be
// saved with smaller than 256 colour palettes
let lzw_minimum_code_size = 8;
writer.write_u8(lzw_minimum_code_size)?;
let mut reader = bitmap.pixels();
lzw_encode(&mut reader, writer, lzw_minimum_code_size as usize)?;

21
libretrogd/src/utils/lzw.rs
View file

@ -383,6 +383,8 @@ impl LzwBytesReader {
}
}
/// Encodes data read from the `src` using LZW (GIF-variant) compression, writing the encoded
/// data out to `dest`. The LZW minimum code bit size is specified via `min_code_size`.
pub fn lzw_encode<S, D>(
src: &mut S,
dest: &mut D,
@ -411,7 +413,9 @@ where
let mut max_code_value_for_bit_size = get_max_code_value_for_bits(current_bit_size);
let mut next_code = initial_table_size as LzwCode + 2;
// begin the output code stream
// begin the output code stream. always write the min_code_size first as a normal byte. then
// write out the clear_code, being sure to encode it using our normal dynamic bit sizing
dest.write_u8(min_code_size as u8)?;
let mut writer = LzwBytesWriter::new(current_bit_size)?;
writer.write_code(dest, clear_code)?;
@ -507,15 +511,18 @@ where
Ok(())
}
/// Decodes data read from the `src` using LZW (GIF-variant) decompression, writing the decoded
/// data out to `dest`.
pub fn lzw_decode<S, D>(
src: &mut S,
dest: &mut D,
min_code_size: usize
) -> Result<(), LzwError>
where
S: ReadBytesExt,
D: WriteBytesExt
{
let min_code_size = src.read_u8()? as usize;
if !is_valid_gif_min_code_size_bits(min_code_size) {
return Err(LzwError::UnsupportedCodeSizeBits(min_code_size));
}
@ -650,17 +657,17 @@ mod tests {
static LZW_TEST_DATA: &[LzwTestData] = &[
LzwTestData {
min_code_size: 2,
packed: &[0x16, 0x8c, 0x2d, 0x99, 0x87, 0x2a, 0x1c, 0xdc, 0x33, 0xa0, 0x02, 0x75, 0xec, 0x95, 0xfa, 0xa8, 0xde, 0x60, 0x8c, 0x04, 0x91, 0x4c, 0x01, 0x00],
packed: &[0x02, 0x16, 0x8c, 0x2d, 0x99, 0x87, 0x2a, 0x1c, 0xdc, 0x33, 0xa0, 0x02, 0x75, 0xec, 0x95, 0xfa, 0xa8, 0xde, 0x60, 0x8c, 0x04, 0x91, 0x4c, 0x01, 0x00],
unpacked: &[1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 0, 0, 0, 0, 2, 2, 2, 1, 1, 1, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1],
},
LzwTestData {
min_code_size: 4,
packed: &[0x21, 0x70, 0x49, 0x79, 0x6a, 0x9d, 0xcb, 0x39, 0x7b, 0xa6, 0xd6, 0x96, 0xa4, 0x3d, 0x0f, 0xd8, 0x8d, 0x64, 0xb9, 0x1d, 0x28, 0xa9, 0x2d, 0x15, 0xfa, 0xc2, 0xf1, 0x37, 0x71, 0x33, 0xc5, 0x61, 0x4b, 0x04, 0x00],
packed: &[0x04, 0x21, 0x70, 0x49, 0x79, 0x6a, 0x9d, 0xcb, 0x39, 0x7b, 0xa6, 0xd6, 0x96, 0xa4, 0x3d, 0x0f, 0xd8, 0x8d, 0x64, 0xb9, 0x1d, 0x28, 0xa9, 0x2d, 0x15, 0xfa, 0xc2, 0xf1, 0x37, 0x71, 0x33, 0xc5, 0x61, 0x4b, 0x04, 0x00],
unpacked: &[11, 11, 11, 11, 11, 7, 7, 7, 7, 7, 11, 11, 11, 11, 14, 14, 7, 7, 7, 7, 11, 11, 11, 14, 14, 14, 14, 7, 7, 7, 11, 11, 14, 14, 15, 15, 14, 14, 7, 7, 11, 14, 14, 15, 15, 15, 15, 14, 14, 7, 7, 14, 14, 15, 15, 15, 15, 14, 14, 11, 7, 7, 14, 14, 15, 15, 14, 14, 11, 11, 7, 7, 7, 14, 14, 14, 14, 11, 11, 11, 7, 7, 7, 7, 14, 14, 11, 11, 11, 11, 7, 7, 7, 7, 7, 11, 11, 11, 11, 11],
},
LzwTestData {
min_code_size: 8,
packed: &[0x0b, 0x00, 0x51, 0xfc, 0x1b, 0x28, 0x70, 0xa0, 0xc1, 0x83, 0x01, 0x01, 0x00],
packed: &[0x08, 0x0b, 0x00, 0x51, 0xfc, 0x1b, 0x28, 0x70, 0xa0, 0xc1, 0x83, 0x01, 0x01, 0x00],
unpacked: &[0x28, 0xff, 0xff, 0xff, 0x28, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff],
}
];
@ -679,10 +686,10 @@ mod tests {
#[test]
fn lzw_decompresses() -> Result<(), LzwError> {
for LzwTestData { packed, unpacked, min_code_size } in LZW_TEST_DATA {
for LzwTestData { packed, unpacked, min_code_size: _ } in LZW_TEST_DATA {
let mut src = Cursor::new(*packed);
let mut dest = vec![0u8; 0];
lzw_decode(&mut src, &mut dest, *min_code_size)?;
lzw_decode(&mut src, &mut dest)?;
assert_eq!(dest, *unpacked);
}