src/util/color.js

class Color {
    /**
     * @typedef {object} RGBObject - An object representing a color in RGB format.
     * @property {number} r - the red component, in the range [0, 255].
     * @property {number} g - the green component, in the range [0, 255].
     * @property {number} b - the blue component, in the range [0, 255].
     */

    /**
     * @typedef {object} HSVObject - An object representing a color in HSV format.
     * @property {number} h - hue, in the range [0-359).
     * @property {number} s - saturation, in the range [0,1].
     * @property {number} v - value, in the range [0,1].
     */

    /** @type {RGBObject} */
    static get RGB_BLACK () {
        return {r: 0, g: 0, b: 0};
    }

    /** @type {RGBObject} */
    static get RGB_WHITE () {
        return {r: 255, g: 255, b: 255};
    }

    /**
     * Convert a Scratch decimal color to a hex string, #RRGGBB.
     * @param {number} decimal RGB color as a decimal.
     * @return {string} RGB color as #RRGGBB hex string.
     */
    static decimalToHex (decimal) {
        if (decimal < 0) {
            decimal += 0xFFFFFF + 1;
        }
        let hex = Math.round(Number(decimal)).toString(16);
        hex = `#${'000000'.substr(0, 6 - hex.length)}${hex}`;
        return hex;
    }

    /**
     * Convert a Scratch decimal color to an RGB color object.
     * @param {number} decimal RGB color as decimal.
     * @return {RGBObject} rgb - {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     */
    static decimalToRgb (decimal) {
        const a = (decimal >> 24) & 0xFF;
        const r = (decimal >> 16) & 0xFF;
        const g = (decimal >> 8) & 0xFF;
        const b = decimal & 0xFF;
        return {r: r, g: g, b: b, a: a > 0 ? a : 255};
    }

    /**
     * Convert a hex color (e.g., F00, #03F, #0033FF) to an RGB color object.
     * @param {!string} hex Hex representation of the color.
     * @return {RGBObject} null on failure, or rgb: {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     */
    static hexToRgb (hex) {
        if (hex.startsWith('#')) {
            hex = hex.substring(1);
        }
        if (hex.length === 8) {
            hex = hex.slice(0, 6);
        }
        const parsed = parseInt(hex, 16);
        if (isNaN(parsed)) {
            return null;
        }
        if (hex.length === 6) {
            return {
                r: (parsed >> 16) & 0xff,
                g: (parsed >> 8) & 0xff,
                b: parsed & 0xff
            };
        } else if (hex.length === 3) {
            const r = ((parsed >> 8) & 0xf);
            const g = ((parsed >> 4) & 0xf);
            const b = parsed & 0xf;
            return {
                r: (r << 4) | r,
                g: (g << 4) | g,
                b: (b << 4) | b
            };
        }
        return null;
    }

    /**
     * Convert an RGB color object to a hex color.
     * @param {RGBObject} rgb - {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     * @return {!string} Hex representation of the color.
     */
    static rgbToHex (rgb) {
        return Color.decimalToHex(Color.rgbToDecimal(rgb));
    }

    /**
     * Convert an RGB color object to a Scratch decimal color.
     * @param {RGBObject} rgb - {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     * @return {!number} Number representing the color.
     */
    static rgbToDecimal (rgb) {
        return (rgb.r << 16) + (rgb.g << 8) + rgb.b;
    }

    /**
    * Convert a hex color (e.g., F00, #03F, #0033FF) to a decimal color number.
    * @param {!string} hex Hex representation of the color.
    * @return {!number} Number representing the color.
    */
    static hexToDecimal (hex) {
        return Color.rgbToDecimal(Color.hexToRgb(hex));
    }

    /**
     * Convert an HSV color to RGB format.
     * @param {HSVObject} hsv - {h: hue [0,360), s: saturation [0,1], v: value [0,1]}
     * @return {RGBObject} rgb - {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     */
    static hsvToRgb (hsv) {
        let h = hsv.h % 360;
        if (h < 0) h += 360;
        const s = Math.max(0, Math.min(hsv.s, 1));
        const v = Math.max(0, Math.min(hsv.v, 1));

        const i = Math.floor(h / 60);
        const f = (h / 60) - i;
        const p = v * (1 - s);
        const q = v * (1 - (s * f));
        const t = v * (1 - (s * (1 - f)));

        let r;
        let g;
        let b;

        switch (i) {
        default:
        case 0:
            r = v;
            g = t;
            b = p;
            break;
        case 1:
            r = q;
            g = v;
            b = p;
            break;
        case 2:
            r = p;
            g = v;
            b = t;
            break;
        case 3:
            r = p;
            g = q;
            b = v;
            break;
        case 4:
            r = t;
            g = p;
            b = v;
            break;
        case 5:
            r = v;
            g = p;
            b = q;
            break;
        }

        return {
            r: Math.floor(r * 255),
            g: Math.floor(g * 255),
            b: Math.floor(b * 255)
        };
    }

    /**
     * Convert an RGB color to HSV format.
     * @param {RGBObject} rgb - {r: red [0,255], g: green [0,255], b: blue [0,255]}.
     * @return {HSVObject} hsv - {h: hue [0,360), s: saturation [0,1], v: value [0,1]}
     */
    static rgbToHsv (rgb) {
        const r = rgb.r / 255;
        const g = rgb.g / 255;
        const b = rgb.b / 255;
        const x = Math.min(Math.min(r, g), b);
        const v = Math.max(Math.max(r, g), b);

        // For grays, hue will be arbitrarily reported as zero. Otherwise, calculate
        let h = 0;
        let s = 0;
        if (x !== v) {
            const f = (r === x) ? g - b : ((g === x) ? b - r : r - g);
            const i = (r === x) ? 3 : ((g === x) ? 5 : 1);
            h = ((i - (f / (v - x))) * 60) % 360;
            s = (v - x) / v;
        }

        return {h: h, s: s, v: v};
    }

    /**
     * Linear interpolation between rgb0 and rgb1.
     * @param {RGBObject} rgb0 - the color corresponding to fraction1 <= 0.
     * @param {RGBObject} rgb1 - the color corresponding to fraction1 >= 1.
     * @param {number} fraction1 - the interpolation parameter. If this is 0.5, for example, mix the two colors equally.
     * @return {RGBObject} the interpolated color.
     */
    static mixRgb (rgb0, rgb1, fraction1) {
        if (fraction1 <= 0) return rgb0;
        if (fraction1 >= 1) return rgb1;
        const fraction0 = 1 - fraction1;
        return {
            r: (fraction0 * rgb0.r) + (fraction1 * rgb1.r),
            g: (fraction0 * rgb0.g) + (fraction1 * rgb1.g),
            b: (fraction0 * rgb0.b) + (fraction1 * rgb1.b)
        };
    }
}

module.exports = Color;