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

/**
 * 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)
 */

THREE.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' )
};