three.js/examples/js/shaders/FreiChenShader.js

( function () {

	/**
 * Edge Detection Shader using Frei-Chen filter
 * Based on http://rastergrid.com/blog/2011/01/frei-chen-edge-detector
 *
 * aspect: vec2 of (1/width, 1/height)
 */

	var FreiChenShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'aspect': {
				value: new THREE.Vector2( 512, 512 )
			}
		},
		vertexShader: [ 'varying vec2 vUv;', 'void main() {', '	vUv = uv;', '	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );', '}' ].join( '\n' ),
		fragmentShader: [ 'uniform sampler2D tDiffuse;', 'varying vec2 vUv;', 'uniform vec2 aspect;', 'vec2 texel = vec2(1.0 / aspect.x, 1.0 / aspect.y);', 'mat3 G[9];', // hard coded matrix values!!!! as suggested in https://github.com/neilmendoza/ofxPostProcessing/blob/master/src/EdgePass.cpp#L45
			'const mat3 g0 = mat3( 0.3535533845424652, 0, -0.3535533845424652, 0.5, 0, -0.5, 0.3535533845424652, 0, -0.3535533845424652 );', 'const mat3 g1 = mat3( 0.3535533845424652, 0.5, 0.3535533845424652, 0, 0, 0, -0.3535533845424652, -0.5, -0.3535533845424652 );', 'const mat3 g2 = mat3( 0, 0.3535533845424652, -0.5, -0.3535533845424652, 0, 0.3535533845424652, 0.5, -0.3535533845424652, 0 );', 'const mat3 g3 = mat3( 0.5, -0.3535533845424652, 0, -0.3535533845424652, 0, 0.3535533845424652, 0, 0.3535533845424652, -0.5 );', 'const mat3 g4 = mat3( 0, -0.5, 0, 0.5, 0, 0.5, 0, -0.5, 0 );', 'const mat3 g5 = mat3( -0.5, 0, 0.5, 0, 0, 0, 0.5, 0, -0.5 );', 'const mat3 g6 = mat3( 0.1666666716337204, -0.3333333432674408, 0.1666666716337204, -0.3333333432674408, 0.6666666865348816, -0.3333333432674408, 0.1666666716337204, -0.3333333432674408, 0.1666666716337204 );', 'const mat3 g7 = mat3( -0.3333333432674408, 0.1666666716337204, -0.3333333432674408, 0.1666666716337204, 0.6666666865348816, 0.1666666716337204, -0.3333333432674408, 0.1666666716337204, -0.3333333432674408 );', 'const mat3 g8 = mat3( 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408, 0.3333333432674408 );', 'void main(void)', '{', '	G[0] = g0,', '	G[1] = g1,', '	G[2] = g2,', '	G[3] = g3,', '	G[4] = g4,', '	G[5] = g5,', '	G[6] = g6,', '	G[7] = g7,', '	G[8] = g8;', '	mat3 I;', '	float cnv[9];', '	vec3 sample;',
			/* fetch the 3x3 neighbourhood and use the RGB vector's length as intensity value */
			'	for (float i=0.0; i<3.0; i++) {', '		for (float j=0.0; j<3.0; j++) {', '			sample = texture2D(tDiffuse, vUv + texel * vec2(i-1.0,j-1.0) ).rgb;', '			I[int(i)][int(j)] = length(sample);', '		}', '	}',
			/* calculate the convolution values for all the masks */
			'	for (int i=0; i<9; i++) {', '		float dp3 = dot(G[i][0], I[0]) + dot(G[i][1], I[1]) + dot(G[i][2], I[2]);', '		cnv[i] = dp3 * dp3;', '	}', '	float M = (cnv[0] + cnv[1]) + (cnv[2] + cnv[3]);', '	float S = (cnv[4] + cnv[5]) + (cnv[6] + cnv[7]) + (cnv[8] + M);', '	gl_FragColor = vec4(vec3(sqrt(M/S)), 1.0);', '}' ].join( '\n' )
	};

	THREE.FreiChenShader = FreiChenShader;

} )();