hayro-syntax 0.8.0

//! Taken from the png crate, see <https://github.com/image-rs/image-png/blob/master/src/filter/mod.rs>

use core::convert::TryInto;

mod paeth;

#[derive(Debug, Clone, Copy)]
#[repr(u8)]
pub(crate) enum BytesPerPixel {
    One = 1,
    Two = 2,
    Three = 3,
    Four = 4,
    Six = 6,
    Eight = 8,
}

// Note: This impl is not from the png crate.
impl BytesPerPixel {
    pub(crate) fn from_row_len(row_len: usize, bpp: usize) -> Option<Self> {
        if !row_len.is_multiple_of(bpp) {
            return None;
        }

        match bpp {
            1 => Some(Self::One),
            2 => Some(Self::Two),
            3 => Some(Self::Three),
            4 => Some(Self::Four),
            6 => Some(Self::Six),
            8 => Some(Self::Eight),
            _ => None,
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub(crate) enum RowFilter {
    NoFilter = 0,
    Sub = 1,
    Up = 2,
    Avg = 3,
    Paeth = 4,
}

impl RowFilter {
    pub(crate) fn from_u8(n: u8) -> Option<Self> {
        match n {
            0 => Some(Self::NoFilter),
            1 => Some(Self::Sub),
            2 => Some(Self::Up),
            3 => Some(Self::Avg),
            4 => Some(Self::Paeth),
            _ => None,
        }
    }
}

pub(crate) fn unfilter(
    mut filter: RowFilter,
    tbpp: BytesPerPixel,
    previous: &[u8],
    current: &mut [u8],
) {
    use self::RowFilter::*;

    // If the previous row is empty, then treat it as if it were filled with zeros.
    if previous.is_empty() {
        if filter == Paeth {
            filter = Sub;
        } else if filter == Up {
            filter = NoFilter;
        }
    }

    match filter {
        NoFilter => {}
        Sub => match tbpp {
            BytesPerPixel::One => {
                current.iter_mut().reduce(|&mut prev, curr| {
                    *curr = curr.wrapping_add(prev);
                    curr
                });
            }
            BytesPerPixel::Two => {
                let mut prev = [0; 2];
                for chunk in current.chunks_exact_mut(2) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0]),
                        chunk[1].wrapping_add(prev[1]),
                    ];
                    *TryInto::<&mut [u8; 2]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Three => {
                let mut prev = [0; 3];
                for chunk in current.chunks_exact_mut(3) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0]),
                        chunk[1].wrapping_add(prev[1]),
                        chunk[2].wrapping_add(prev[2]),
                    ];
                    *TryInto::<&mut [u8; 3]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Four => {
                let mut prev = [0; 4];
                for chunk in current.chunks_exact_mut(4) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0]),
                        chunk[1].wrapping_add(prev[1]),
                        chunk[2].wrapping_add(prev[2]),
                        chunk[3].wrapping_add(prev[3]),
                    ];
                    *TryInto::<&mut [u8; 4]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Six => {
                let mut prev = [0; 6];
                for chunk in current.chunks_exact_mut(6) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0]),
                        chunk[1].wrapping_add(prev[1]),
                        chunk[2].wrapping_add(prev[2]),
                        chunk[3].wrapping_add(prev[3]),
                        chunk[4].wrapping_add(prev[4]),
                        chunk[5].wrapping_add(prev[5]),
                    ];
                    *TryInto::<&mut [u8; 6]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Eight => {
                let mut prev = [0; 8];
                for chunk in current.chunks_exact_mut(8) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0]),
                        chunk[1].wrapping_add(prev[1]),
                        chunk[2].wrapping_add(prev[2]),
                        chunk[3].wrapping_add(prev[3]),
                        chunk[4].wrapping_add(prev[4]),
                        chunk[5].wrapping_add(prev[5]),
                        chunk[6].wrapping_add(prev[6]),
                        chunk[7].wrapping_add(prev[7]),
                    ];
                    *TryInto::<&mut [u8; 8]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
        },
        Up => {
            for (curr, &above) in current.iter_mut().zip(previous) {
                *curr = curr.wrapping_add(above);
            }
        }
        Avg if previous.is_empty() => match tbpp {
            BytesPerPixel::One => {
                current.iter_mut().reduce(|&mut prev, curr| {
                    *curr = curr.wrapping_add(prev / 2);
                    curr
                });
            }
            BytesPerPixel::Two => {
                let mut prev = [0; 2];
                for chunk in current.chunks_exact_mut(2) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0] / 2),
                        chunk[1].wrapping_add(prev[1] / 2),
                    ];
                    *TryInto::<&mut [u8; 2]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Three => {
                let mut prev = [0; 3];
                for chunk in current.chunks_exact_mut(3) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0] / 2),
                        chunk[1].wrapping_add(prev[1] / 2),
                        chunk[2].wrapping_add(prev[2] / 2),
                    ];
                    *TryInto::<&mut [u8; 3]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Four => {
                let mut prev = [0; 4];
                for chunk in current.chunks_exact_mut(4) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0] / 2),
                        chunk[1].wrapping_add(prev[1] / 2),
                        chunk[2].wrapping_add(prev[2] / 2),
                        chunk[3].wrapping_add(prev[3] / 2),
                    ];
                    *TryInto::<&mut [u8; 4]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Six => {
                let mut prev = [0; 6];
                for chunk in current.chunks_exact_mut(6) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0] / 2),
                        chunk[1].wrapping_add(prev[1] / 2),
                        chunk[2].wrapping_add(prev[2] / 2),
                        chunk[3].wrapping_add(prev[3] / 2),
                        chunk[4].wrapping_add(prev[4] / 2),
                        chunk[5].wrapping_add(prev[5] / 2),
                    ];
                    *TryInto::<&mut [u8; 6]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
            BytesPerPixel::Eight => {
                let mut prev = [0; 8];
                for chunk in current.chunks_exact_mut(8) {
                    let new_chunk = [
                        chunk[0].wrapping_add(prev[0] / 2),
                        chunk[1].wrapping_add(prev[1] / 2),
                        chunk[2].wrapping_add(prev[2] / 2),
                        chunk[3].wrapping_add(prev[3] / 2),
                        chunk[4].wrapping_add(prev[4] / 2),
                        chunk[5].wrapping_add(prev[5] / 2),
                        chunk[6].wrapping_add(prev[6] / 2),
                        chunk[7].wrapping_add(prev[7] / 2),
                    ];
                    *TryInto::<&mut [u8; 8]>::try_into(chunk).unwrap() = new_chunk;
                    prev = new_chunk;
                }
            }
        },
        Avg => match tbpp {
            BytesPerPixel::One => {
                let mut lprev = [0; 1];
                for (chunk, above) in current.chunks_exact_mut(1).zip(previous.chunks_exact(1)) {
                    let new_chunk =
                        [chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8)];
                    *TryInto::<&mut [u8; 1]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
            BytesPerPixel::Two => {
                let mut lprev = [0; 2];
                for (chunk, above) in current.chunks_exact_mut(2).zip(previous.chunks_exact(2)) {
                    let new_chunk = [
                        chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8),
                        chunk[1].wrapping_add(((above[1] as u16 + lprev[1] as u16) / 2) as u8),
                    ];
                    *TryInto::<&mut [u8; 2]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
            BytesPerPixel::Three => {
                let mut lprev = [0; 3];
                for (chunk, above) in current.chunks_exact_mut(3).zip(previous.chunks_exact(3)) {
                    let new_chunk = [
                        chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8),
                        chunk[1].wrapping_add(((above[1] as u16 + lprev[1] as u16) / 2) as u8),
                        chunk[2].wrapping_add(((above[2] as u16 + lprev[2] as u16) / 2) as u8),
                    ];
                    *TryInto::<&mut [u8; 3]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
            BytesPerPixel::Four => {
                let mut lprev = [0; 4];
                for (chunk, above) in current.chunks_exact_mut(4).zip(previous.chunks_exact(4)) {
                    let new_chunk = [
                        chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8),
                        chunk[1].wrapping_add(((above[1] as u16 + lprev[1] as u16) / 2) as u8),
                        chunk[2].wrapping_add(((above[2] as u16 + lprev[2] as u16) / 2) as u8),
                        chunk[3].wrapping_add(((above[3] as u16 + lprev[3] as u16) / 2) as u8),
                    ];
                    *TryInto::<&mut [u8; 4]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
            BytesPerPixel::Six => {
                let mut lprev = [0; 6];
                for (chunk, above) in current.chunks_exact_mut(6).zip(previous.chunks_exact(6)) {
                    let new_chunk = [
                        chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8),
                        chunk[1].wrapping_add(((above[1] as u16 + lprev[1] as u16) / 2) as u8),
                        chunk[2].wrapping_add(((above[2] as u16 + lprev[2] as u16) / 2) as u8),
                        chunk[3].wrapping_add(((above[3] as u16 + lprev[3] as u16) / 2) as u8),
                        chunk[4].wrapping_add(((above[4] as u16 + lprev[4] as u16) / 2) as u8),
                        chunk[5].wrapping_add(((above[5] as u16 + lprev[5] as u16) / 2) as u8),
                    ];
                    *TryInto::<&mut [u8; 6]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
            BytesPerPixel::Eight => {
                let mut lprev = [0; 8];
                for (chunk, above) in current.chunks_exact_mut(8).zip(previous.chunks_exact(8)) {
                    let new_chunk = [
                        chunk[0].wrapping_add(((above[0] as u16 + lprev[0] as u16) / 2) as u8),
                        chunk[1].wrapping_add(((above[1] as u16 + lprev[1] as u16) / 2) as u8),
                        chunk[2].wrapping_add(((above[2] as u16 + lprev[2] as u16) / 2) as u8),
                        chunk[3].wrapping_add(((above[3] as u16 + lprev[3] as u16) / 2) as u8),
                        chunk[4].wrapping_add(((above[4] as u16 + lprev[4] as u16) / 2) as u8),
                        chunk[5].wrapping_add(((above[5] as u16 + lprev[5] as u16) / 2) as u8),
                        chunk[6].wrapping_add(((above[6] as u16 + lprev[6] as u16) / 2) as u8),
                        chunk[7].wrapping_add(((above[7] as u16 + lprev[7] as u16) / 2) as u8),
                    ];
                    *TryInto::<&mut [u8; 8]>::try_into(chunk).unwrap() = new_chunk;
                    lprev = new_chunk;
                }
            }
        },
        Paeth => paeth::unfilter(tbpp, previous, current),
    }
}