/**
 * @author zz85 / http://www.lab4games.net/zz85/blog
 *
 * Triangle blur shader
 * based on glfx.js triangle blur shader
 * https://github.com/evanw/glfx.js
 *
 * A basic blur filter, which convolves the image with a
 * pyramid filter. The pyramid filter is separable and is applied as two
 * perpendicular triangle filters.
 */

import {
	Vector2
} from "../../../build/three.module.js";

var TriangleBlurShader = {

	uniforms: {

		"texture": { value: null },
		"delta": { value: new Vector2( 1, 1 ) }

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

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

		"}"

	].join( "\n" ),

	fragmentShader: [

		"#include <common>",

		"#define ITERATIONS 10.0",

		"uniform sampler2D texture;",
		"uniform vec2 delta;",

		"varying vec2 vUv;",

		"void main() {",

		"	vec4 color = vec4( 0.0 );",

		"	float total = 0.0;",

		// randomize the lookup values to hide the fixed number of samples

		"	float offset = rand( vUv );",

		"	for ( float t = -ITERATIONS; t <= ITERATIONS; t ++ ) {",

		"		float percent = ( t + offset - 0.5 ) / ITERATIONS;",
		"		float weight = 1.0 - abs( percent );",

		"		color += texture2D( texture, vUv + delta * percent ) * weight;",
		"		total += weight;",

		"	}",

		"	gl_FragColor = color / total;",

		"}"

	].join( "\n" )

};

export { TriangleBlurShader };
