# All files / fast-colors/src color-blending.ts

81.52% Statements 75/92
58.06% Branches 18/31
90.91% Functions 20/22
81.52% Lines 75/92

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     import {
        hslToRGB,
        labToRGB,
        lchToRGB,
        rgbToHSL,
        rgbToLAB,
        rgbToLCH,
    } from "./color-converters";
    import { ColorHSL } from "./color-hsl";
    import { ColorLAB } from "./color-lab";
    import { ColorLCH } from "./color-lch";
    import { ColorRGBA64 } from "./color-rgba-64";
    import { clamp } from "./math-utilities";

    // The alpha channel of the input is ignored
    export function saturateViaLCH(
        input: ColorRGBA64,
        saturation: number,
        saturationConstant: number = 18
    ): ColorRGBA64 {
        const lch: ColorLCH = rgbToLCH(input);
        let sat: number = lch.c + saturation * saturationConstant;
        if (sat < 0) {
            sat = 0;
        }
        return lchToRGB(new ColorLCH(lch.l, sat, lch.h));
    }

    // The alpha channel of the input is ignored
    export function desaturateViaLCH(
        input: ColorRGBA64,
        saturation: number,
        saturationConstant: number = 18
    ): ColorRGBA64 {
        return saturateViaLCH(input, -1 * saturation, saturationConstant);
    }

    // The alpha channel of the input is ignored
    export function darkenViaLAB(
        input: ColorRGBA64,
        amount: number,
        darkenConstant: number = 18
    ): ColorRGBA64 {
        const lab: ColorLAB = rgbToLAB(input);
        const darkened: number = lab.l - amount * darkenConstant;
        return labToRGB(new ColorLAB(darkened, lab.a, lab.b));
    }

    // The alpha channel of the input is ignored
    export function lightenViaLAB(
        input: ColorRGBA64,
        amount: number,
        darkenConstant: number = 18
    ): ColorRGBA64 {
        return darkenViaLAB(input, -1 * amount, darkenConstant);
    }

    export function blendBurnChannel(bottom: number, top: number): number {
        if (top === 0.0) {
            // Despite the discontinuity, other sources seem to use 0.0 here instead of 1
            return 0.0;
        }
        return 1.0 - (1.0 - bottom) / top;
    }

    // The alpha channel of the input is ignored
    export function blendBurn(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendBurnChannel(bottom.r, top.r),
            blendBurnChannel(bottom.g, top.g),
            blendBurnChannel(bottom.b, top.b),
            1
        );
    }

    // The alpha channel of the input is ignored
    export function blendColor(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        const bottomHSL: ColorHSL = rgbToHSL(bottom);
        const topHSL: ColorHSL = rgbToHSL(top);

        if (topHSL.s === 0) {
            return new ColorRGBA64(bottomHSL.l, bottomHSL.l, bottomHSL.l, 1);
        }

        return hslToRGB(new ColorHSL(topHSL.h, topHSL.s, bottomHSL.l));
    }

    export function blendDarkenChannel(bottom: number, top: number): number {
        return Math.min(bottom, top);
    }

    // The alpha channel of the input is ignored
    export function blendDarken(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendDarkenChannel(bottom.r, top.r),
            blendDarkenChannel(bottom.g, top.g),
            blendDarkenChannel(bottom.b, top.b),
            1
        );
    }

    export function blendDodgeChannel(bottom: number, top: number): number {
        if (top >= 1.0) {
            return 1.0;
        }
        const retVal: number = bottom / (1.0 - top);
        if (retVal >= 1.0) {
            return 1.0;
        }
        return retVal;
    }

    // The alpha channel of the input is ignored
    export function blendDodge(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendDodgeChannel(bottom.r, top.r),
            blendDodgeChannel(bottom.g, top.g),
            blendDodgeChannel(bottom.b, top.b),
            1
        );
    }

    export function blendLightenChannel(bottom: number, top: number): number {
        return Math.max(bottom, top);
    }

    // The alpha channel of the input is ignored
    export function blendLighten(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendLightenChannel(bottom.r, top.r),
            blendLightenChannel(bottom.g, top.g),
            blendLightenChannel(bottom.b, top.b),
            1
        );
    }

    export function blendMultiplyChannel(bottom: number, top: number): number {
        return bottom * top;
    }

    // The alpha channel of the input is ignored
    export function blendMultiply(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendMultiplyChannel(bottom.r, top.r),
            blendMultiplyChannel(bottom.g, top.g),
            blendMultiplyChannel(bottom.b, top.b),
            1
        );
    }

    export function blendOverlayChannel(bottom: number, top: number): number {
        if (bottom < 0.5) {
            return clamp(2.0 * top * bottom, 0, 1);
        }
        return clamp(1.0 - 2.0 * (1.0 - top) * (1.0 - bottom), 0, 1);
    }

    // The alpha channel of the input is ignored
    export function blendOverlay(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendOverlayChannel(bottom.r, top.r),
            blendOverlayChannel(bottom.g, top.g),
            blendOverlayChannel(bottom.b, top.b),
            1
        );
    }

    export function blendScreenChannel(bottom: number, top: number): number {
        return 1.0 - (1.0 - top) * (1.0 - bottom);
    }

    // The alpha channel of the input is ignored
    export function blendScreen(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        return new ColorRGBA64(
            blendScreenChannel(bottom.r, top.r),
            blendScreenChannel(bottom.g, top.g),
            blendScreenChannel(bottom.b, top.b),
            1
        );
    }

    export enum ColorBlendMode {
        Burn,
        Color,
        Darken,
        Dodge,
        Lighten,
        Multiply,
        Overlay,
        Screen,
    }

    // The alpha channel of the input is ignored
    export function blend(
        mode: ColorBlendMode,
        bottom: ColorRGBA64,
        top: ColorRGBA64
    ): ColorRGBA64 {
        switch (mode) {
            case ColorBlendMode.Burn:
                return blendBurn(bottom, top);
            case ColorBlendMode.Color:
                return blendColor(bottom, top);
            case ColorBlendMode.Darken:
                return blendDarken(bottom, top);
            case ColorBlendMode.Dodge:
                return blendDodge(bottom, top);
            case ColorBlendMode.Lighten:
                return blendLighten(bottom, top);
            case ColorBlendMode.Multiply:
                return blendMultiply(bottom, top);
            case ColorBlendMode.Overlay:
                return blendOverlay(bottom, top);
            case ColorBlendMode.Screen:
                return blendScreen(bottom, top);
            default:
                throw new Error("Unknown blend mode");
        }
    }

    // Alpha channel of bottom is ignored
    // The returned color always has an alpha channel of 1
    // Different programs (eg: paint.net, photoshop) will give different answers than this occasionally but within +/- 1/255 in each channel. Just depends on the details of how they round off decimals
    export function computeAlphaBlend(bottom: ColorRGBA64, top: ColorRGBA64): ColorRGBA64 {
        Iif (top.a >= 1) {
            return top;
        } else Iif (top.a <= 0) {
            return new ColorRGBA64(bottom.r, bottom.g, bottom.b, 1);
        }

        const r: number = top.a * top.r + (1 - top.a) * bottom.r;
        const g: number = top.a * top.g + (1 - top.a) * bottom.g;
        const b: number = top.a * top.b + (1 - top.a) * bottom.b;

        return new ColorRGBA64(r, g, b, 1);
    }