/**
 * @module SepiaShader
 * @three_import import { SepiaShader } from 'three/addons/shaders/SepiaShader.js';
 */

/**
 * Sepia tone shader based on [glfx.js sepia shader]{@link https://github.com/evanw/glfx.js}.
 *
 * @constant
 * @type {ShaderMaterial~Shader}
 */
const SepiaShader = {

	name: 'SepiaShader',

	uniforms: {

		'tDiffuse': { value: null },
		'amount': { value: 1.0 }

	},

	vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {

			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,

	fragmentShader: /* glsl */`

		uniform float amount;

		uniform sampler2D tDiffuse;

		varying vec2 vUv;

		void main() {

			vec4 color = texture2D( tDiffuse, vUv );
			vec3 c = color.rgb;

			color.r = dot( c, vec3( 1.0 - 0.607 * amount, 0.769 * amount, 0.189 * amount ) );
			color.g = dot( c, vec3( 0.349 * amount, 1.0 - 0.314 * amount, 0.168 * amount ) );
			color.b = dot( c, vec3( 0.272 * amount, 0.534 * amount, 1.0 - 0.869 * amount ) );

			gl_FragColor = vec4( min( vec3( 1.0 ), color.rgb ), color.a );

		}`

};

export { SepiaShader };
