pi-frame-server/src/imageproc.rs

use image::ColorType::Rgb8;

use image::RgbImage;

use palette::{cast::FromComponents, color_difference::EuclideanDistance, FromColor, IntoColor, Oklab, 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 Into<Srgb> for DisplayColor {
    fn into(self) -> Srgb {
        DISPLAY_PALETTE[self 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),
        }
    }
}

/// Buffer to be sent to the EInk display.
#[derive(Debug)]
pub struct EInkBuffer {
    data: Vec<DisplayColor>,
    width: usize,
    height: usize,
}

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 trait Ditherer {
    fn dither(&self, img: &RgbImage) -> 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 (nearest, dist) = DISPLAY_PALETTE
        .iter()
        .enumerate()
        .map(|(idx, p_color)| {
            let lab: Oklab = p_color.clone().into_color();
            (idx, color.distance(p_color.into_format()))
        })
        .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) -> EInkBuffer {
        assert!(img.width() == 800);
        assert!(img.height() == 480);
        let mut buf = EInkBuffer::new(800, 480);
        // img.enumerate_pixels().for_each(|(x, y, pix)| {
        //     buf[x + y * 800] = nearest_neighbor(Srgb::from_components());
        // });
        let srgb = <&[Srgb<u8>]>::from_components(&**img);
        buf
    }
}