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

/**
 * @author zz85 / https://github.com/zz85 | https://www.lab4games.net/zz85/blog
 *
 * 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" )
};