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//! Utility functions related to handling of
//! [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm).
/// Describes which stage of
/// [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm)
/// applies to a decoded row.
///
/// See also [Reader.next_interlaced_row](crate::decoder::Reader::next_interlaced_row).
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Adam7Info {
pub(crate) pass: u8,
pub(crate) line: u32,
pub(crate) width: u32,
}
impl Adam7Info {
/// Creates a new `Adam7Info`. May panic if the arguments are out of range (e.g. if `pass` is
/// 0 or greater than 8).
///
/// * `pass` corresponds to a pass of the
/// [the Adam7 algorithm](https://en.wikipedia.org/wiki/Adam7_algorithm)
/// * `line` is the number of a line within a pass (starting with 0). For example,
/// in an image of height 8, `line` can be beteween `0..4` in the 7th `pass`
/// (those 4 interlaced rows correspond to 2nd, 4th, 6th, and 8th row of the full image).
/// * `width` describes how many pixels are in an interlaced row. For example,
/// in the 7th `pass`, the `width` is be the same as full image width, but in
/// in the 1st `pass`, the `width` is be 1/8th of the image width (rounded up as
/// necessary).
///
/// Note that in typical usage, `Adam7Info`s are returned by [Reader.next_interlaced_row]
/// and there is no need to create them by calling `Adam7Info::new`. `Adam7Info::new` is
/// nevertheless exposed as a public API, because it helps to provide self-contained example
/// usage of [expand_interlaced_row](crate::expand_interlaced_row).
pub fn new(pass: u8, line: u32, width: u32) -> Self {
assert!(1 <= pass && pass <= 7);
assert!(width > 0);
Self { pass, line, width }
}
}
/// This iterator iterates over the different passes of an image Adam7 encoded
/// PNG image
/// The pattern is:
/// 16462646
/// 77777777
/// 56565656
/// 77777777
/// 36463646
/// 77777777
/// 56565656
/// 77777777
///
#[derive(Clone)]
pub(crate) struct Adam7Iterator {
line: u32,
lines: u32,
line_width: u32,
current_pass: u8,
width: u32,
height: u32,
}
impl Adam7Iterator {
pub fn new(width: u32, height: u32) -> Adam7Iterator {
let mut this = Adam7Iterator {
line: 0,
lines: 0,
line_width: 0,
current_pass: 1,
width,
height,
};
this.init_pass();
this
}
/// Calculates the bounds of the current pass
fn init_pass(&mut self) {
let w = f64::from(self.width);
let h = f64::from(self.height);
let (line_width, lines) = match self.current_pass {
1 => (w / 8.0, h / 8.0),
2 => ((w - 4.0) / 8.0, h / 8.0),
3 => (w / 4.0, (h - 4.0) / 8.0),
4 => ((w - 2.0) / 4.0, h / 4.0),
5 => (w / 2.0, (h - 2.0) / 4.0),
6 => ((w - 1.0) / 2.0, h / 2.0),
7 => (w, (h - 1.0) / 2.0),
_ => unreachable!(),
};
self.line_width = line_width.ceil() as u32;
self.lines = lines.ceil() as u32;
self.line = 0;
}
}
/// Iterates over `Adam7Info`s.
impl Iterator for Adam7Iterator {
type Item = Adam7Info;
fn next(&mut self) -> Option<Self::Item> {
if self.line < self.lines && self.line_width > 0 {
let this_line = self.line;
self.line += 1;
Some(Adam7Info {
pass: self.current_pass,
line: this_line,
width: self.line_width,
})
} else if self.current_pass < 7 {
self.current_pass += 1;
self.init_pass();
self.next()
} else {
None
}
}
}
fn subbyte_pixels(scanline: &[u8], bits_pp: usize) -> impl Iterator<Item = u8> + '_ {
(0..scanline.len() * 8)
.step_by(bits_pp)
.map(move |bit_idx| {
let byte_idx = bit_idx / 8;
// sub-byte samples start in the high-order bits
let rem = 8 - bit_idx % 8 - bits_pp;
match bits_pp {
// evenly divides bytes
1 => (scanline[byte_idx] >> rem) & 1,
2 => (scanline[byte_idx] >> rem) & 3,
4 => (scanline[byte_idx] >> rem) & 15,
_ => unreachable!(),
}
})
}
/// Given `row_stride`, interlace `info`, and bits-per-pixel, produce an iterator of bit positions
/// of pixels to copy from the input scanline to the image buffer. The positions are expressed as
/// bit offsets from position (0,0) in the frame that is currently being decoded.
fn expand_adam7_bits(
row_stride_in_bytes: usize,
info: &Adam7Info,
bits_pp: usize,
) -> impl Iterator<Item = usize> {
let line_no = info.line as usize;
let pass = info.pass;
let interlaced_width = info.width as usize;
let (line_mul, line_off, samp_mul, samp_off) = match pass {
1 => (8, 0, 8, 0),
2 => (8, 0, 8, 4),
3 => (8, 4, 4, 0),
4 => (4, 0, 4, 2),
5 => (4, 2, 2, 0),
6 => (2, 0, 2, 1),
7 => (2, 1, 1, 0),
_ => {
// `Adam7Info.pass` is a non-`pub`lic field. `InterlaceInfo` is expected
// to maintain an invariant that `pass` is valid.
panic!("Invalid `Adam7Info.pass`");
}
};
// the equivalent line number in progressive scan
let prog_line = line_mul * line_no + line_off;
let line_start = prog_line * row_stride_in_bytes * 8;
(0..interlaced_width)
.map(move |i| i * samp_mul + samp_off)
.map(move |i| i * bits_pp)
.map(move |bits_offset| bits_offset + line_start)
}
/// Copies pixels from `interlaced_row` into the right location in `img`.
///
/// First bytes of `img` should belong to the top-left corner of the currently decoded frame.
///
/// `img_row_stride` specifies an offset in bytes between subsequent rows of `img`.
/// This can be the width of the current frame being decoded, but this is not required - a bigger
/// stride may be useful if the frame being decoded is a sub-region of `img`.
///
/// `interlaced_row` and `interlace_info` typically come from
/// [crate::decoder::Reader::next_interlaced_row], but this is not required. In particular, before
/// calling `expand_interlaced_row` one may need to expand the decoded row, so that its format and
/// `bits_per_pixel` matches that of `img`. Note that in initial Adam7 passes the `interlaced_row`
/// may contain less pixels that the width of the frame being decoded (e.g. it contains only 1/8th
/// of pixels in the initial pass).
///
/// Example:
///
/// ```
/// use png::{expand_interlaced_row, Adam7Info};
/// let info = Adam7Info::new(5, 0, 4); // 1st line of 5th pass has 4 pixels.
/// let mut img = vec![0; 8 * 8];
/// let row = vec![1, 2, 3, 4];
/// expand_interlaced_row(&mut img, 8, &row, &info, 8);
/// assert_eq!(&img, &[
/// 0, 0, 0, 0, 0, 0, 0, 0,
/// 0, 0, 0, 0, 0, 0, 0, 0,
/// 1, 0, 2, 0, 3, 0, 4, 0, // <= this is where the 1st line of 5s appears
/// 0, 0, 0, 0, 0, 0, 0, 0, // in the schematic drawing of the passes at
/// 0, 0, 0, 0, 0, 0, 0, 0, // https://en.wikipedia.org/wiki/Adam7_algorithm
/// 0, 0, 0, 0, 0, 0, 0, 0,
/// 0, 0, 0, 0, 0, 0, 0, 0,
/// 0, 0, 0, 0, 0, 0, 0, 0,
/// ]);
/// ```
pub fn expand_pass(
img: &mut [u8],
img_row_stride: usize,
interlaced_row: &[u8],
interlace_info: &Adam7Info,
bits_per_pixel: u8,
) {
let bits_pp = bits_per_pixel as usize;
let bit_indices = expand_adam7_bits(img_row_stride, interlace_info, bits_pp);
if bits_pp < 8 {
for (pos, px) in bit_indices.zip(subbyte_pixels(interlaced_row, bits_pp)) {
let rem = 8 - pos % 8 - bits_pp;
img[pos / 8] |= px << rem as u8;
}
} else {
let bytes_pp = bits_pp / 8;
for (bitpos, px) in bit_indices.zip(interlaced_row.chunks(bytes_pp)) {
for (offset, val) in px.iter().enumerate() {
img[bitpos / 8 + offset] = *val;
}
}
}
}
#[test]
fn test_adam7() {
/*
1646
7777
5656
7777
*/
let it = Adam7Iterator::new(4, 4);
let passes: Vec<_> = it.collect();
assert_eq!(
&*passes,
&[
Adam7Info {
pass: 1,
line: 0,
width: 1
},
Adam7Info {
pass: 4,
line: 0,
width: 1
},
Adam7Info {
pass: 5,
line: 0,
width: 2
},
Adam7Info {
pass: 6,
line: 0,
width: 2
},
Adam7Info {
pass: 6,
line: 1,
width: 2
},
Adam7Info {
pass: 7,
line: 0,
width: 4
},
Adam7Info {
pass: 7,
line: 1,
width: 4
}
]
);
}
#[test]
fn test_subbyte_pixels() {
let scanline = &[0b10101010, 0b10101010];
let pixels = subbyte_pixels(scanline, 1).collect::<Vec<_>>();
assert_eq!(pixels.len(), 16);
assert_eq!(pixels, [1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0]);
}
#[test]
fn test_expand_adam7_bits() {
let width = 32;
let bits_pp = 1;
let stride = width / 8;
let info = |pass, line, img_width| create_adam7_info_for_tests(pass, line as u32, img_width);
let expected = |offset: usize, step: usize, count: usize| {
(0..count)
.map(move |i| step * i + offset)
.collect::<Vec<_>>()
};
for line_no in 0..8 {
let start = 8 * line_no * width;
assert_eq!(
expand_adam7_bits(stride, &info(1, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 8, 4)
);
let start = start + 4;
assert_eq!(
expand_adam7_bits(stride, &info(2, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 8, 4)
);
let start = (8 * line_no + 4) * width;
assert_eq!(
expand_adam7_bits(stride, &info(3, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 4, 8)
);
}
for line_no in 0..16 {
let start = 4 * line_no * width + 2;
assert_eq!(
expand_adam7_bits(stride, &info(4, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 4, 8)
);
let start = (4 * line_no + 2) * width;
assert_eq!(
expand_adam7_bits(stride, &info(5, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 2, 16)
)
}
for line_no in 0..32 {
let start = 2 * line_no * width + 1;
assert_eq!(
expand_adam7_bits(stride, &info(6, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 2, 16),
"line_no: {}",
line_no
);
let start = (2 * line_no + 1) * width;
assert_eq!(
expand_adam7_bits(stride, &info(7, line_no, width), bits_pp).collect::<Vec<_>>(),
expected(start, 1, 32)
);
}
}
#[test]
fn test_expand_adam7_bits_independent_row_stride() {
let pass = 1;
let line_no = 1;
let width = 32;
let bits_pp = 8;
let info = create_adam7_info_for_tests;
{
let stride = width;
assert_eq!(
expand_adam7_bits(stride, &info(pass, line_no, width), bits_pp).collect::<Vec<_>>(),
vec![2048, 2112, 2176, 2240],
);
}
{
let stride = 10000;
assert_eq!(
expand_adam7_bits(stride, &info(pass, line_no, width), bits_pp).collect::<Vec<_>>(),
vec![640000, 640064, 640128, 640192],
);
}
}
#[test]
fn test_expand_pass_subbyte() {
let mut img = [0u8; 8];
let width = 8;
let stride = width / 8;
let bits_pp = 1;
let info = create_adam7_info_for_tests;
expand_pass(&mut img, stride, &[0b10000000], &info(1, 0, width), bits_pp);
assert_eq!(img, [0b10000000u8, 0, 0, 0, 0, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b10000000], &info(2, 0, width), bits_pp);
assert_eq!(img, [0b10001000u8, 0, 0, 0, 0, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b11000000], &info(3, 0, width), bits_pp);
assert_eq!(img, [0b10001000u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b11000000], &info(4, 0, width), bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b11000000], &info(4, 1, width), bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10101010, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b11110000], &info(5, 0, width), bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0, 0]);
expand_pass(&mut img, stride, &[0b11110000], &info(5, 1, width), bits_pp);
assert_eq!(
img,
[0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, stride, &[0b11110000], &info(6, 0, width), bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, stride, &[0b11110000], &info(6, 1, width), bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b11111111, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, stride, &[0b11110000], &info(6, 2, width), bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b10101010, 0]
);
expand_pass(&mut img, stride, &[0b11110000], &info(6, 3, width), bits_pp);
assert_eq!(
[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b11111111, 0],
img
);
expand_pass(&mut img, stride, &[0b11111111], &info(7, 0, width), bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0,
0b11111111,
0,
0b11111111,
0
],
img
);
expand_pass(&mut img, stride, &[0b11111111], &info(7, 1, width), bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0,
0b11111111,
0
],
img
);
expand_pass(&mut img, stride, &[0b11111111], &info(7, 2, width), bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0
],
img
);
expand_pass(&mut img, stride, &[0b11111111], &info(7, 3, width), bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111
],
img
);
}
#[cfg(test)]
fn create_adam7_info_for_tests(pass: u8, line: u32, img_width: usize) -> Adam7Info {
let width = {
let img_height = 8;
Adam7Iterator::new(img_width as u32, img_height)
.filter(|info| info.pass == pass)
.map(|info| info.width)
.next()
.unwrap()
};
Adam7Info { pass, line, width }
}