142 lines
4.6 KiB
Rust
142 lines
4.6 KiB
Rust
use crate::error::PngError;
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pub fn filter_line(filter: u8, bpp: usize, data: &[u8], last_line: &[u8], buf: &mut Vec<u8>) {
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assert!(data.len() >= bpp);
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assert!(last_line.is_empty() || data.len() == last_line.len());
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buf.reserve(data.len());
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match filter {
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0 => {
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buf.extend_from_slice(data);
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}
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1 => {
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buf.extend_from_slice(&data[0..bpp]);
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buf.extend(
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data.iter()
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.skip(bpp)
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.zip(data.iter())
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.map(|(cur, last)| cur.wrapping_sub(*last)),
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);
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}
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2 => {
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if last_line.is_empty() {
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buf.extend_from_slice(data);
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} else {
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assert_eq!(data.len(), last_line.len());
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buf.extend(
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data.iter()
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.zip(last_line.iter())
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.map(|(cur, last)| cur.wrapping_sub(*last)),
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);
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};
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}
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3 => {
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for (i, byte) in data.iter().enumerate() {
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if last_line.is_empty() {
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buf.push(match i.checked_sub(bpp) {
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Some(x) => byte.wrapping_sub(data[x] >> 1),
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None => *byte,
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});
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} else {
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buf.push(match i.checked_sub(bpp) {
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Some(x) => byte.wrapping_sub(
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((u16::from(data[x]) + u16::from(last_line[i])) >> 1) as u8,
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),
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None => byte.wrapping_sub(last_line[i] >> 1),
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});
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};
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}
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}
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4 => {
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for (i, byte) in data.iter().enumerate() {
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if last_line.is_empty() {
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buf.push(match i.checked_sub(bpp) {
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Some(x) => byte.wrapping_sub(data[x]),
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None => *byte,
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});
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} else {
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buf.push(match i.checked_sub(bpp) {
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Some(x) => {
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byte.wrapping_sub(paeth_predictor(data[x], last_line[i], last_line[x]))
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}
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None => byte.wrapping_sub(last_line[i]),
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});
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};
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}
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}
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_ => unreachable!(),
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}
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}
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pub fn unfilter_line(
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filter: u8,
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bpp: usize,
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data: &[u8],
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last_line: &[u8],
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buf: &mut Vec<u8>,
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) -> Result<(), PngError> {
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buf.clear();
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buf.reserve(data.len());
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assert!(data.len() >= bpp);
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assert_eq!(data.len(), last_line.len());
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match filter {
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0 => {
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buf.extend_from_slice(data);
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}
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1 => {
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for (i, &cur) in data.iter().enumerate() {
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let prev_byte = i.checked_sub(bpp).and_then(|x| buf.get(x).copied());
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buf.push(match prev_byte {
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Some(b) => cur.wrapping_add(b),
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None => cur,
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});
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}
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}
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2 => {
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buf.extend(
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data.iter()
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.zip(last_line)
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.map(|(&cur, &last)| cur.wrapping_add(last)),
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);
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}
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3 => {
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for (i, (&cur, &last)) in data.iter().zip(last_line).enumerate() {
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let prev_byte = i.checked_sub(bpp).and_then(|x| buf.get(x).copied());
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buf.push(match prev_byte {
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Some(b) => cur.wrapping_add(((u16::from(b) + u16::from(last)) >> 1) as u8),
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None => cur.wrapping_add(last >> 1),
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});
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}
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}
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4 => {
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for (i, (&cur, &up)) in data.iter().zip(last_line).enumerate() {
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buf.push(
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match i
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.checked_sub(bpp)
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.map(|x| (buf.get(x).copied(), last_line.get(x).copied()))
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{
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Some((Some(left), Some(left_up))) => {
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cur.wrapping_add(paeth_predictor(left, up, left_up))
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}
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_ => cur.wrapping_add(up),
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},
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);
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}
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}
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_ => return Err(PngError::InvalidData),
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}
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Ok(())
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}
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fn paeth_predictor(a: u8, b: u8, c: u8) -> u8 {
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let p = i32::from(a) + i32::from(b) - i32::from(c);
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let pa = (p - i32::from(a)).abs();
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let pb = (p - i32::from(b)).abs();
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let pc = (p - i32::from(c)).abs();
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if pa <= pb && pa <= pc {
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a
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} else if pb <= pc {
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b
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} else {
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c
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}
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}
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