From 62e0fec044b5727efa1841138f44d9a1d9537bcf Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Sat, 2 May 2020 13:48:07 -0400
Subject: color/order: Implement color orderings

---
 src/color/order.rs | 196 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 196 insertions(+)
 create mode 100644 src/color/order.rs

(limited to 'src/color')

diff --git a/src/color/order.rs b/src/color/order.rs
new file mode 100644
index 0000000..300a556
--- /dev/null
+++ b/src/color/order.rs
@@ -0,0 +1,196 @@
+//! Linear orders for colors.
+
+use super::source::ColorSource;
+use super::Rgb8;
+
+use crate::hilbert::hilbert_point;
+
+use rand::seq::SliceRandom;
+use rand::Rng;
+
+use std::cmp::Ordering;
+
+/// An iterator over all colors from a source.
+#[derive(Debug)]
+struct ColorSourceIter<S> {
+    source: S,
+    coords: Vec<usize>,
+}
+
+impl<S: ColorSource> From<S> for ColorSourceIter<S> {
+    fn from(source: S) -> Self {
+        let coords = vec![0; source.dimensions().len()];
+
+        Self { source, coords }
+    }
+}
+
+impl<S: ColorSource> Iterator for ColorSourceIter<S> {
+    type Item = Rgb8;
+
+    fn next(&mut self) -> Option<Rgb8> {
+        if self.coords.is_empty() {
+            return None;
+        }
+
+        let color = self.source.get_color(&self.coords);
+
+        let dims = self.source.dimensions();
+        for i in 0..dims.len() {
+            self.coords[i] += 1;
+            if self.coords[i] < dims[i] {
+                break;
+            } else if i == dims.len() - 1 {
+                self.coords.clear();
+            } else {
+                self.coords[i] = 0;
+            }
+        }
+
+        Some(color)
+    }
+}
+
+/// Wrapper for sorting colors by hue.
+#[derive(Debug, Eq, PartialEq)]
+struct Hue {
+    /// The quadrant of the hue angle.
+    quad: i32,
+    /// The numerator of the hue calculation.
+    num: i32,
+    /// The denominator of the hue calculation.
+    denom: i32,
+}
+
+impl From<Rgb8> for Hue {
+    fn from(rgb8: Rgb8) -> Self {
+        // The hue angle is atan2(sqrt(3) * (G - B), 2 * R - G - B).  We avoid actually computing
+        // the atan2() as an optimization.
+        let r = rgb8[0] as i32;
+        let g = rgb8[1] as i32;
+        let b = rgb8[2] as i32;
+
+        let num = g - b;
+        let mut denom = 2 * r - g - b;
+        if num == 0 && denom == 0 {
+            denom = 1;
+        }
+
+        let quad = match (num >= 0, denom >= 0) {
+            (true, true) => 0,
+            (true, false) => 1,
+            (false, false) => 2,
+            (false, true) => 3,
+        };
+
+        Self { quad, num, denom }
+    }
+}
+
+impl Ord for Hue {
+    fn cmp(&self, other: &Self) -> Ordering {
+        // Within the same quadrant,
+        //
+        //     atan2(n1, d1) < atan2(n2, d2)  iff
+        //           n1 / d1 < n2 / d2        iff
+        //           n1 * d2 < n2 * d1
+        self.quad
+            .cmp(&other.quad)
+            .then_with(|| (self.num * other.denom).cmp(&(other.num * self.denom)))
+    }
+}
+
+impl PartialOrd for Hue {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+/// Iterate over colors sorted by their hue.
+pub fn hue_sorted<S: ColorSource>(source: S) -> Vec<Rgb8> {
+    let mut colors: Vec<_> = ColorSourceIter::from(source).collect();
+    colors.sort_by_key(|c| Hue::from(*c));
+    colors
+}
+
+/// Iterate over colors in random order.
+pub fn shuffled<S: ColorSource, R: Rng>(source: S, rng: &mut R) -> Vec<Rgb8> {
+    let mut colors: Vec<_> = ColorSourceIter::from(source).collect();
+    colors.shuffle(rng);
+    colors
+}
+
+/// ceil(log_2(n)). for rounding up to powers of 2.
+fn log2(n: usize) -> u32 {
+    let nbits = 8 * std::mem::size_of::<usize>() as u32;
+    nbits - (n - 1).leading_zeros()
+}
+
+/// Iterate over colors in Morton order (Z-order).
+pub fn morton<S: ColorSource>(source: S) -> Vec<Rgb8> {
+    let mut colors = Vec::new();
+
+    let dims = source.dimensions();
+    let ndims = dims.len();
+
+    let nbits = ndims * dims.iter().map(|n| log2(*n) as usize).max().unwrap();
+
+    let size = 1usize << nbits;
+    let mut coords = vec![0; ndims];
+    for i in 0..size {
+        for x in &mut coords {
+            *x = 0;
+        }
+        for j in 0..nbits {
+            let bit = (i >> j) & 1;
+            coords[j % ndims] |= bit << (j / ndims);
+        }
+        if coords.iter().zip(dims.iter()).all(|(x, n)| x < n) {
+            colors.push(source.get_color(&coords));
+        }
+    }
+
+    colors
+}
+
+/// Iterate over colors in Hilbert curve order.
+pub fn hilbert<S: ColorSource>(source: S) -> Vec<Rgb8> {
+    let mut colors = Vec::new();
+
+    let dims = source.dimensions();
+    let ndims = dims.len();
+
+    let bits: Vec<_> = dims.iter().map(|n| log2(*n)).collect();
+    let nbits: u32 = bits.iter().sum();
+    let size = 1usize << nbits;
+
+    let mut coords = vec![0; ndims];
+
+    for i in 0..size {
+        hilbert_point(i, &bits, &mut coords);
+        if coords.iter().zip(dims.iter()).all(|(x, n)| x < n) {
+            colors.push(source.get_color(&coords));
+        }
+    }
+
+    colors
+}
+
+/// Stripe an ordered list of colors, to reduce artifacts in the generated image.
+///
+/// The striped ordering gives every other item first, then every other item from the remaining
+/// items, etc. For example, the striped form of `0..16` is
+/// `[0, 2, 4, 6, 8, 10, 12, 14, 1, 5, 9, 13, 3, 11, 7, 15]`.
+pub fn striped(colors: Vec<Rgb8>) -> Vec<Rgb8> {
+    let len = colors.len();
+    let mut result = Vec::with_capacity(len);
+    let mut stripe = 1;
+    while stripe <= len {
+        for i in ((stripe - 1)..len).step_by(2 * stripe) {
+            result.push(colors[i]);
+        }
+        stripe *= 2;
+    }
+
+    result
+}
-- 
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