This is how I UNroll

unroll.fs

float find_closest(int x, int y, float c0) {
	/*
	Original looping code, from http://devlog-martinsh.blogspot.com.es/2011/03/glsl-dithering.html
	vec4 dither[4];

	dither[0] = vec4( 1.0, 33.0, 9.0, 41.0);
	dither[1] = vec4(49.0, 17.0, 57.0, 25.0);
	dither[2] = vec4(13.0, 45.0, 5.0, 37.0);
	dither[3] = vec4(61.0, 29.0, 53.0, 21.0);

	float limit = 0.0;
	if(x < 4) {
		limit = (dither[x][y]+1.0)/64.0;
	}
	*/
	
	// Now adapted for WebGL shaders

	vec4 dither0 = vec4( 1.0, 33.0, 9.0, 41.0);
	vec4 dither1 = vec4(49.0, 17.0, 57.0, 25.0);
	vec4 dither2 = vec4(13.0, 45.0, 5.0, 37.0);
	vec4 dither3 = vec4(61.0, 29.0, 53.0, 21.0);
	
	float limit = 0.0;
	float value = 0.0;
	
	vec4 dither;
	
	if(x == 0) {
		dither = dither0;
	} else if(x == 1) {
		dither = dither1;
	} else if(x == 2) {
		dither = dither2;
	} else if(x == 3) {
		dither = dither3;
	}
	
	if(x < 4) {
		if(y == 0) {
			value = dither[0];
		} else if(y == 1) {
			value = dither[1];
		} else if(y == 2) {
			value = dither[2];
		} else if(y == 3) {
			value = dither[3];
		}
	
		limit = (value + 1.0) / 64.0;
	}

	if(c0 < limit) {
		return 0.0;
	} else {
		return 1.0;
	}
}