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

/**
 * 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.
 */

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 };
