//! Utility functions
use std::iter::StepBy;
use std::ops::Range;
/// 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;
}
/// The current pass#.
pub fn current_pass(&self) -> u8 {
self.current_pass
}
}
/// Iterates over the (passes, lines, widths)
impl Iterator for Adam7Iterator {
type Item = (u8, u32, u32);
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((self.current_pass, this_line, 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 pass, image width, and line number, produce an iterator of bit positions of pixels to copy
/// from the input scanline to the image buffer.
fn expand_adam7_bits(
pass: u8,
width: usize,
line_no: usize,
bits_pp: usize,
) -> StepBy<Range<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),
_ => panic!("Adam7 pass out of range: {}", pass),
};
// the equivalent line number in progressive scan
let prog_line = line_mul * line_no + line_off;
// line width is rounded up to the next byte
let line_width = (width * bits_pp + 7) & !7;
let line_start = prog_line * line_width;
let start = line_start + (samp_off * bits_pp);
let stop = line_start + (width * bits_pp);
(start..stop).step_by(bits_pp * samp_mul)
}
/// Expands an Adam 7 pass
pub fn expand_pass(
img: &mut [u8],
width: u32,
scanline: &[u8],
pass: u8,
line_no: u32,
bits_pp: u8,
) {
let width = width as usize;
let line_no = line_no as usize;
let bits_pp = bits_pp as usize;
// pass is out of range but don't blow up
if pass == 0 || pass > 7 {
return;
}
let bit_indices = expand_adam7_bits(pass, width, line_no, bits_pp);
if bits_pp < 8 {
for (pos, px) in bit_indices.zip(subbyte_pixels(scanline, 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(scanline.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,
&[
(1, 0, 1),
(4, 0, 1),
(5, 0, 2),
(6, 0, 2),
(6, 1, 2),
(7, 0, 4),
(7, 1, 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 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(1, width, line_no, bits_pp).collect::<Vec<_>>(),
expected(start, 8, 4)
);
let start = start + 4;
assert_eq!(
expand_adam7_bits(2, width, line_no, bits_pp).collect::<Vec<_>>(),
expected(start, 8, 4)
);
let start = (8 * line_no + 4) * width;
assert_eq!(
expand_adam7_bits(3, width, line_no, 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(4, width, line_no, bits_pp).collect::<Vec<_>>(),
expected(start, 4, 8)
);
let start = (4 * line_no + 2) * width;
assert_eq!(
expand_adam7_bits(5, width, line_no, 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(6, width, line_no, bits_pp).collect::<Vec<_>>(),
expected(start, 2, 16),
"line_no: {}",
line_no
);
let start = (2 * line_no + 1) * width;
assert_eq!(
expand_adam7_bits(7, width, line_no, bits_pp).collect::<Vec<_>>(),
expected(start, 1, 32)
);
}
}
#[test]
fn test_expand_pass_subbyte() {
let mut img = [0u8; 8];
let width = 8;
let bits_pp = 1;
expand_pass(&mut img, width, &[0b10000000], 1, 0, bits_pp);
assert_eq!(img, [0b10000000u8, 0, 0, 0, 0, 0, 0, 0]);
expand_pass(&mut img, width, &[0b10000000], 2, 0, bits_pp);
assert_eq!(img, [0b10001000u8, 0, 0, 0, 0, 0, 0, 0]);
expand_pass(&mut img, width, &[0b11000000], 3, 0, bits_pp);
assert_eq!(img, [0b10001000u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
expand_pass(&mut img, width, &[0b11000000], 4, 0, bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10001000, 0, 0, 0]);
expand_pass(&mut img, width, &[0b11000000], 4, 1, bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0, 0, 0b10101010, 0, 0, 0]);
expand_pass(&mut img, width, &[0b11110000], 5, 0, bits_pp);
assert_eq!(img, [0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0, 0]);
expand_pass(&mut img, width, &[0b11110000], 5, 1, bits_pp);
assert_eq!(
img,
[0b10101010u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, width, &[0b11110000], 6, 0, bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b10101010, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, width, &[0b11110000], 6, 1, bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b11111111, 0, 0b10101010, 0, 0b10101010, 0]
);
expand_pass(&mut img, width, &[0b11110000], 6, 2, bits_pp);
assert_eq!(
img,
[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b10101010, 0]
);
expand_pass(&mut img, width, &[0b11110000], 6, 3, bits_pp);
assert_eq!(
[0b11111111u8, 0, 0b11111111, 0, 0b11111111, 0, 0b11111111, 0],
img
);
expand_pass(&mut img, width, &[0b11111111], 7, 0, bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0,
0b11111111,
0,
0b11111111,
0
],
img
);
expand_pass(&mut img, width, &[0b11111111], 7, 1, bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0,
0b11111111,
0
],
img
);
expand_pass(&mut img, width, &[0b11111111], 7, 2, bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0
],
img
);
expand_pass(&mut img, width, &[0b11111111], 7, 3, bits_pp);
assert_eq!(
[
0b11111111u8,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111,
0b11111111
],
img
);
}
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