text: import {
  	Vector2
  } from '../../../build/three.module.js';
  
  /**
   * Sobel Edge Detection (see https://youtu.be/uihBwtPIBxM)
   *
   * As mentioned in the video the Sobel operator expects a grayscale image as input.
   *
   */
  
  var SobelOperatorShader = {
  
  	uniforms: {
  
  		'tDiffuse': { value: null },
  		'resolution': { value: new Vector2() }
  
  	},
  
  	vertexShader: [
  
  		'varying vec2 vUv;',
  
  		'void main() {',
  
  		'	vUv = uv;',
  
  		'	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',
  
  		'}'
  
  	].join( '\n' ),
  
  	fragmentShader: [
  
  		'uniform sampler2D tDiffuse;',
  		'uniform vec2 resolution;',
  		'varying vec2 vUv;',
  
  		'void main() {',
  
  		'	vec2 texel = vec2( 1.0 / resolution.x, 1.0 / resolution.y );',
  
  		// kernel definition (in glsl matrices are filled in column-major order)
  
  		'	const mat3 Gx = mat3( -1, -2, -1, 0, 0, 0, 1, 2, 1 );', // x direction kernel
  		'	const mat3 Gy = mat3( -1, 0, 1, -2, 0, 2, -1, 0, 1 );', // y direction kernel
  
  		// fetch the 3x3 neighbourhood of a fragment
  
  		// first column
  
  		'	float tx0y0 = texture2D( tDiffuse, vUv + texel * vec2( -1, -1 ) ).r;',
  		'	float tx0y1 = texture2D( tDiffuse, vUv + texel * vec2( -1,  0 ) ).r;',
  		'	float tx0y2 = texture2D( tDiffuse, vUv + texel * vec2( -1,  1 ) ).r;',
  
  		// second column
  
  		'	float tx1y0 = texture2D( tDiffuse, vUv + texel * vec2(  0, -1 ) ).r;',
  		'	float tx1y1 = texture2D( tDiffuse, vUv + texel * vec2(  0,  0 ) ).r;',
  		'	float tx1y2 = texture2D( tDiffuse, vUv + texel * vec2(  0,  1 ) ).r;',
  
  		// third column
  
  		'	float tx2y0 = texture2D( tDiffuse, vUv + texel * vec2(  1, -1 ) ).r;',
  		'	float tx2y1 = texture2D( tDiffuse, vUv + texel * vec2(  1,  0 ) ).r;',
  		'	float tx2y2 = texture2D( tDiffuse, vUv + texel * vec2(  1,  1 ) ).r;',
  
  		// gradient value in x direction
  
  		'	float valueGx = Gx[0][0] * tx0y0 + Gx[1][0] * tx1y0 + Gx[2][0] * tx2y0 + ',
  		'		Gx[0][1] * tx0y1 + Gx[1][1] * tx1y1 + Gx[2][1] * tx2y1 + ',
  		'		Gx[0][2] * tx0y2 + Gx[1][2] * tx1y2 + Gx[2][2] * tx2y2; ',
  
  		// gradient value in y direction
  
  		'	float valueGy = Gy[0][0] * tx0y0 + Gy[1][0] * tx1y0 + Gy[2][0] * tx2y0 + ',
  		'		Gy[0][1] * tx0y1 + Gy[1][1] * tx1y1 + Gy[2][1] * tx2y1 + ',
  		'		Gy[0][2] * tx0y2 + Gy[1][2] * tx1y2 + Gy[2][2] * tx2y2; ',
  
  		// magnitute of the total gradient
  
  		'	float G = sqrt( ( valueGx * valueGx ) + ( valueGy * valueGy ) );',
  
  		'	gl_FragColor = vec4( vec3( G ), 1 );',
  
  		'}'
  
  	].join( '\n' )
  
  };
  
  export { SobelOperatorShader };
  