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use super::Pixel;
struct VQBox<'a> {
pixels: &'a mut [Pixel],
max: Pixel,
min: Pixel,
}
fn avg_u8(a: u8, b: u8) -> u8 {
(a & b) + ((a ^ b) >> 1)
}
impl<'a> VQBox<'a> {
fn new(pixels: &'a mut [Pixel]) -> Self {
let mut max = Pixel{ r: 0, g: 0, b: 0 };
let mut min = Pixel{ r: 255, g: 255, b: 255 };
for pix in pixels.iter() {
max = max.max(*pix);
min = min.min(*pix);
}
Self { pixels, max, min }
}
fn can_split(&self) -> bool {
let dr = self.max.r - self.min.r;
let dg = self.max.g - self.min.g;
let db = self.max.b - self.min.b;
(dr | dg | db) != 0
}
fn sort<F>(arr: &mut [Pixel], idx: F) -> usize where F: Fn(&Pixel) -> usize {
let mut buckets: Vec<Vec<Pixel>> = Vec::with_capacity(256);
let mut counts = [0; 256];
for pix in arr.iter() {
counts[idx(pix)] += 1;
}
for i in 0..256 {
buckets.push(Vec::with_capacity(counts[i]));
}
for pix in arr.iter() {
buckets[idx(pix)].push(*pix);
}
let mut start = 0;
let mut pivot = 0;
let mut cand1 = 0;
for bucket in buckets.iter() {
let end = bucket.len();
if (start > 0) && (start <= arr.len() / 2) {
pivot = start + end;
cand1 = start;
}
arr[start..][..end].copy_from_slice(bucket.as_slice());
start += end;
}
for bucket in buckets.iter() {
if pivot != 0 {
break;
}
pivot += bucket.len();
}
if pivot < arr.len() || cand1 == 0 {
pivot
} else {
cand1
}
}
fn calc_min_and_max(pixels: &[Pixel]) -> (Pixel, Pixel) {
let mut max = Pixel{ r: 0, g: 0, b: 0 };
let mut min = Pixel{ r: 255, g: 255, b: 255 };
for pix in pixels.iter() {
max = max.max(*pix);
min = min.min(*pix);
}
(min, max)
}
fn split(self) -> (VQBox<'a>, VQBox<'a>) {
let dr = self.max.r - self.min.r;
let dg = self.max.g - self.min.g;
let db = self.max.b - self.min.b;
let box0;
let box1;
if (dr > dg) && (dr >= db) {
let pivot = Self::sort(self.pixels, |pix| pix.r as usize);
let (part0, part1) = self.pixels.split_at_mut(pivot);
let (min0, max0) = Self::calc_min_and_max(part0);
let (min1, max1) = Self::calc_min_and_max(part1);
box0 = VQBox { pixels: part0, max: max0, min: min0 };
box1 = VQBox { pixels: part1, max: max1, min: min1 };
} else if (db > dr) && (db > dg) {
let pivot = Self::sort(self.pixels, |pix| pix.b as usize);
let (part0, part1) = self.pixels.split_at_mut(pivot);
let (min0, max0) = Self::calc_min_and_max(part0);
let (min1, max1) = Self::calc_min_and_max(part1);
box0 = VQBox { pixels: part0, max: max0, min: min0 };
box1 = VQBox { pixels: part1, max: max1, min: min1 };
} else {
let pivot = Self::sort(self.pixels, |pix| pix.g as usize);
let (part0, part1) = self.pixels.split_at_mut(pivot);
let (min0, max0) = Self::calc_min_and_max(part0);
let (min1, max1) = Self::calc_min_and_max(part1);
box0 = VQBox { pixels: part0, max: max0, min: min0 };
box1 = VQBox { pixels: part1, max: max1, min: min1 };
}
(box0, box1)
}
}
pub fn quantise_median_cut(src: &[Pixel], pal: &mut [[u8; 3]; 256]) -> usize {
let mut pixels = Vec::with_capacity(src.len());
pixels.extend_from_slice(src);
VQBox::sort(pixels.as_mut_slice(), |pix| pix.r as usize);
VQBox::sort(pixels.as_mut_slice(), |pix| pix.g as usize);
VQBox::sort(pixels.as_mut_slice(), |pix| pix.b as usize);
let box0 = VQBox::new(pixels.as_mut_slice());
let mut boxes: Vec<VQBox> = Vec::with_capacity(256);
boxes.push(box0);
let mut changed = true;
while changed && boxes.len() < 256 {
let end = boxes.len();
changed = false;
let mut split_largest = false;
for _ in 0..end {
let curbox = boxes.remove(0);
if curbox.can_split() {
let (box0, box1) = curbox.split();
boxes.push(box0);
boxes.push(box1);
changed = true;
} else {
boxes.push(curbox);
split_largest = true;
break;
}
if boxes.len() == 256 {
break;
}
}
if split_largest {
let mut maxidx = 0;
let mut lcount = 0;
for (i, cbox) in boxes.iter().enumerate() {
if cbox.can_split() && cbox.pixels.len() > lcount {
lcount = cbox.pixels.len();
maxidx = i;
}
}
if lcount > 0 {
let curbox = boxes.remove(maxidx);
let (box0, box1) = curbox.split();
boxes.push(box0);
boxes.push(box1);
changed = true;
}
}
}
for (curbox, palentry) in boxes.iter().zip(pal.iter_mut()) {
palentry[0] = avg_u8(curbox.min.r, curbox.max.r);
palentry[1] = avg_u8(curbox.min.g, curbox.max.g);
palentry[2] = avg_u8(curbox.min.b, curbox.max.b);
}
boxes.len()
}
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