import { clamp, runFragmentShader } from '../canvas';


export type SepiaOptions = {
    amount: number;
}

export function sepia(
    image: HTMLImageElement | HTMLCanvasElement,
    canvas: HTMLCanvasElement, 
    options: SepiaOptions
) {
    runFragmentShader(image, canvas, `
        precision highp float;
        uniform sampler2D texture;
        uniform float amount;
        varying vec2 texCoord;
        void main() {
            vec4 color = texture2D(texture, texCoord);
            float r = color.r;
            float g = color.g;
            float b = color.b;
            
            color.r = min(1.0, (r * (1.0 - (0.607 * amount))) + (g * (0.769 * amount)) + (b * (0.189 * amount)));
            color.g = min(1.0, (r * 0.349 * amount) + (g * (1.0 - (0.314 * amount))) + (b * 0.168 * amount));
            color.b = min(1.0, (r * 0.272 * amount) + (g * 0.534 * amount) + (b * (1.0 - (0.869 * amount))));
            
            gl_FragColor = color;
        }
    `, {
        amount: clamp(-1, options.amount, 1),
    });
}

export default sepia;