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" )
};