whoshue/src/analysis/mod.rs

//! Analysis always uses source pixels, never the scaled preview.
use std::collections::HashMap;

use crate::capture::Frame;

pub const HUE_BINS: usize = 36;
pub const NEUTRAL_SATURATION: f32 = 0.05;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Region {
    pub x: u32,
    pub y: u32,
    pub width: u32,
    pub height: u32,
}

impl Region {
    pub fn full(frame: &Frame) -> Self {
        Self {
            x: 0,
            y: 0,
            width: frame.width,
            height: frame.height,
        }
    }

    pub fn crop(self, frame: &Frame) -> Vec<u8> {
        let mut pixels = Vec::new();
        for y in self.y..self.y.saturating_add(self.height).min(frame.height) {
            let start =
                ((y as usize * frame.width as usize) + self.x.min(frame.width) as usize) * 4;
            let end = ((y as usize * frame.width as usize)
                + self.x.saturating_add(self.width).min(frame.width) as usize)
                * 4;
            pixels.extend_from_slice(&frame.rgba[start..end]);
        }
        pixels
    }
}

#[derive(Clone, Debug)]
pub struct Swatch {
    pub rgb: [u8; 3],
    pub count: u64,
}

pub struct Analysis {
    pub palette: Vec<Swatch>,
    pub pixels: u64,
    pub neutral_pixels: u64,
    pub neutral_colors: u64,
    pub hue_pixels: [u64; HUE_BINS],
    pub hue_colors: [u64; HUE_BINS],
}

impl Default for Analysis {
    fn default() -> Self {
        Self {
            palette: Vec::new(),
            pixels: 0,
            neutral_pixels: 0,
            neutral_colors: 0,
            hue_pixels: [0; HUE_BINS],
            hue_colors: [0; HUE_BINS],
        }
    }
}

/// HSV hue in degrees, saturation and value in 0..=1.
pub fn hsv(rgb: [u8; 3]) -> [f32; 3] {
    let [r, g, b] = rgb.map(|v| v as f32 / 255.0);
    let max = r.max(g).max(b);
    let min = r.min(g).min(b);
    let delta = max - min;
    if delta == 0.0 {
        return [0.0, 0.0, max];
    }
    let hue = if max == r {
        ((g - b) / delta).rem_euclid(6.0)
    } else if max == g {
        (b - r) / delta + 2.0
    } else {
        (r - g) / delta + 4.0
    };
    [hue * 60.0, delta / max, max]
}

pub fn analyze(rgba: &[u8]) -> Analysis {
    let mut counts = HashMap::<[u8; 3], u64>::new();
    for pixel in rgba.as_chunks::<4>().0 {
        // Ignore fully transparent pixels; count other captured RGB values exactly.
        if pixel[3] != 0 {
            *counts.entry([pixel[0], pixel[1], pixel[2]]).or_default() += 1;
        }
    }
    let mut result = Analysis::default();
    for (rgb, count) in counts {
        result.pixels += count;
        let [h, s, _] = hsv(rgb);
        if s < NEUTRAL_SATURATION {
            result.neutral_pixels += count;
            result.neutral_colors += 1;
        } else {
            let bin = (h / 10.0).floor() as usize % HUE_BINS;
            result.hue_pixels[bin] += count;
            result.hue_colors[bin] += 1;
        }
        result.palette.push(Swatch { rgb, count });
    }
    result
        .palette
        .sort_unstable_by(|a, b| b.count.cmp(&a.count).then(a.rgb.cmp(&b.rgb)));
    result
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn primary_hues_and_wraparound() {
        assert_eq!(hsv([255, 0, 0]), [0.0, 1.0, 1.0]);
        assert_eq!(hsv([0, 255, 0])[0], 120.0);
        assert_eq!(hsv([0, 0, 255])[0], 240.0);
        assert!(hsv([255, 0, 1])[0] > 359.0);
        assert_eq!(hsv([0, 0, 0]), [0.0, 0.0, 0.0]);
    }

    #[test]
    fn frequency_distinct_weights_neutrals_and_transparency() {
        let data = [
            255, 0, 0, 255, 255, 0, 0, 255, 128, 0, 0, 255, 0, 255, 0, 255, 128, 128, 128, 255,
            255, 0, 255, 0,
        ];
        let a = analyze(&data);
        assert_eq!(a.pixels, 5);
        assert_eq!(a.palette.len(), 4);
        assert_eq!(a.palette[0].rgb, [255, 0, 0]);
        assert_eq!(a.hue_pixels[0], 3);
        assert_eq!(a.hue_colors[0], 2);
        assert_eq!(a.neutral_pixels, 1);
        assert_eq!(
            a.hue_pixels.iter().sum::<u64>() + a.neutral_pixels,
            a.pixels
        );
    }

    #[test]
    fn crop_uses_source_coordinates_and_clamps() {
        let frame = Frame {
            seq: 0,
            width: 3,
            height: 2,
            rgba: (0..24).collect(),
        };
        let r = Region {
            x: 1,
            y: 0,
            width: 1,
            height: 2,
        };
        assert_eq!(r.crop(&frame), [4, 5, 6, 7, 16, 17, 18, 19]);
        let edge = Region {
            x: 2,
            y: 1,
            width: 10,
            height: 10,
        };
        assert_eq!(edge.crop(&frame), [20, 21, 22, 23]);
    }
}