pi-frame-server/src/imageproc.rs

use image::RgbImage;

use palette::{cast::FromComponents, color_difference::Ciede2000, IntoColor, Lab, Srgb};

/// Palette used on the display; pixels can be one of these colors.
///
/// The RGB values are slightly adjusted to improve accuracy.
const DISPLAY_PALETTE: [Srgb; 7] = [
    Srgb::new(0.047, 0.047, 0.055), // Black
    Srgb::new(0.824, 0.824, 0.816), // White
    Srgb::new(0.118, 0.376, 0.122), // Green
    Srgb::new(0.114, 0.118, 0.667), // Blue
    Srgb::new(0.549, 0.106, 0.114), // Red
    Srgb::new(0.827, 0.788, 0.239), // Yellow
    Srgb::new(0.757, 0.443, 0.165), // Orange
];

// fn octcolor_rgb(color: &OctColor) -> &Srgb<u8> {
//     match color {
//         OctColor::Black => &DISPLAY_PALETTE[0],
//         OctColor::White => &DISPLAY_PALETTE[1],
//         OctColor::Green => &DISPLAY_PALETTE[2],
//         OctColor::Blue => &DISPLAY_PALETTE[3],
//         OctColor::Red => &DISPLAY_PALETTE[4],
//         OctColor::Yellow => &DISPLAY_PALETTE[5],
//         OctColor::Orange => &DISPLAY_PALETTE[6],
//         OctColor::HiZ => &DISPLAY_PALETTE[1],
//     }
// }

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum DisplayColor {
    Black,
    White,
    Green,
    Blue,
    Red,
    Yellow,
    Orange,
}

impl From<DisplayColor> for Srgb {
    fn from(value: DisplayColor) -> Self {
        DISPLAY_PALETTE[value as usize]
    }
}

impl DisplayColor {
    fn from_u8(value: u8) -> Self {
        match value {
            0 => Self::Black,
            1 => Self::White,
            2 => Self::Green,
            3 => Self::Blue,
            4 => Self::Red,
            5 => Self::Yellow,
            6 => Self::Orange,
            _ => panic!("unexpected DisplayColor {}", value),
        }
    }

    fn into_byte(color1: Self, color2: Self) -> u8 {
        let upper: u8 = color1.into();
        let lower: u8 = color2.into();
        upper << 4 | lower
    }
}
impl From<DisplayColor> for u8 {
    fn from(value: DisplayColor) -> Self {
        value as u8
    }
}
/// Buffer to be sent to the EInk display.
#[derive(Debug)]
pub struct EInkBuffer(Vec<DisplayColor>);

impl EInkBuffer {
    pub fn into_display_buffer(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(self.0.len()/2);

        for colors in self.0.chunks_exact(2) {
            buf.push(DisplayColor::into_byte(colors[0], colors[1]));
        }

        buf
    }
    pub fn new(width: usize, height: usize) -> Self {
        let v = vec![DisplayColor::Black; width * height];
        EInkBuffer(v)
    }
}

// impl EInkBuffer {
//     /// Converts the EInkBuffer into data that can be sent over the SPI API
//     /// Bin-packs the two 4-bit colors into bytes.
//     pub fn into_buffer(&self) -> Vec<u8> {
//         vec![]
//     }
//
//     pub fn new(width: usize, height: usize) -> EInkBuffer {
//         EInkBuffer {
//             data: vec![DisplayColor::Black; width * height],
//             width,
//             height,
//         }
//     }
//     pub fn set(&mut self, x: usize, y: usize, value: DisplayColor) {
//         self.data[x + y * self.width] = value;
//     }
//     pub fn get(&self, x:usize, y:usize) -> DisplayColor {
//         self.data[x 
//     }
// }

pub trait Ditherer {
    fn dither(&self, img: &RgbImage, output: &mut EInkBuffer);
}

// fn color_distance(c1: LinSrgb, c2: LinSrgb) -> f32 {
//     let r2 = (c2.red - c1.red).powf(2.0);
//     let g2 = (c2.green - c1.green).powf(2.0);
//     let b2 = (c2.blue - c1.blue).powf(2.0);
//
//     (r2 + g2 + b2).sqrt()
// }

/// Find the closest approximate palette color to the given sRGB value.
/// This uses euclidian distance in linear space.
pub fn nearest_neighbor(color: Srgb) -> (DisplayColor, f32) {
    let input: Lab = color.into_color();

    let (nearest, dist) = DISPLAY_PALETTE
        .iter()
        .enumerate()
        .map(|(idx, p_color)| {
            let c: Lab = (*p_color).into_color();
            (idx, input.difference(c))
        })
        .min_by(|(_, a), (_, b)| a.total_cmp(b))
        .unwrap();
    (DisplayColor::from_u8(nearest as u8), dist)
}

pub struct NNDither();

impl Ditherer for NNDither {
    fn dither(&self, img: &RgbImage, output: &mut EInkBuffer) {
        assert!(img.width() == 800);
        assert!(img.height() == 480);
        
        // sRGB view into the given image. zero copy!
        let srgb = <&[Srgb<u8>]>::from_components(&**img);

        for (idx, pixel) in srgb.iter().enumerate() {
            let (n, _) = nearest_neighbor(pixel.into_format());
            output.0[idx] = n;
        }

    }
}