8x8bayer.glsl

uniform sampler2D texture, smpPalette;
uniform vec2 paletteSize;
varying vec4 vertTexCoord;
int dither[64];

vec3 nearestColour(vec3 col){
	float dist, minDist = 999.;
	vec2 pixelSize = vec2(1. / paletteSize.xy);
	vec3 outCol, palCol;
	for (float x = 0.; x < 1.; x += pixelSize.x) {
		for (float y = 0.; y < 1.; y += pixelSize.y) {
			palCol = vec3(texture2D(smpPalette, vec2(x + pixelSize.x * .5, y + pixelSize.y * .5)).rgb);
			if (palCol == col) return col;
			dist = (palCol.r - col.r) * (palCol.r - col.r)	+ (palCol.g - col.g) * (palCol.g - col.g) + (palCol.b - col.b) * (palCol.b - col.b);		
			if (dist < minDist) {
				minDist = dist;
				outCol = palCol;
			}  
		}
	}
	return outCol;
}

vec4 dither8x8(vec2 position, vec4 col) {
	vec3 preCol = vec3(col.rgb);
    int X = int(mod(position.x, 8.0));
    int Y = int(mod(position.y, 8.0));
    dither[0]  = 0;
    dither[1]  = 32;
    dither[2]  = 8;
    dither[3]  = 40;
    dither[4]  = 2;
    dither[5]  = 34;
    dither[6]  = 10;
    dither[7]  = 42;
    dither[8]  = 48;
    dither[9]  = 16;
    dither[10] = 56;
    dither[11] = 24;
    dither[12] = 50;
    dither[13] = 18;
    dither[14] = 58;
    dither[15] = 26;
    dither[16] = 12;
    dither[17] = 44;
    dither[18] = 4;
    dither[19] = 36;
    dither[20] = 14;
    dither[21] = 46;
    dither[22] = 6;
    dither[23] = 38;
    dither[24] = 60;
    dither[25] = 28;
    dither[26] = 52;
    dither[27] = 20;
    dither[28] = 62;
    dither[29] = 30;
    dither[30] = 54;
    dither[31] = 22;
    dither[32] = 3;
    dither[33] = 35;
    dither[34] = 11;
    dither[35] = 43;
    dither[36] = 1;
    dither[37] = 33;
    dither[38] = 9;
    dither[39] = 41;
    dither[40] = 51;
    dither[41] = 19;
    dither[42] = 59;
    dither[43] = 27;
    dither[44] = 49;
    dither[45] = 17;
    dither[46] = 57;
    dither[47] = 25;
    dither[48] = 15;
    dither[49] = 47;
    dither[50] = 7;
    dither[51] = 39;
    dither[52] = 13;
    dither[53] = 45;
    dither[54] = 5;
    dither[55] = 37;
    dither[56] = 63;
    dither[57] = 31;
    dither[58] = 55;
    dither[59] = 23;
    dither[60] = 61;
    dither[61] = 29;
    dither[62] = 53;
    dither[63] = 21;
    
    float match = float(dither[8 * Y + X]) / 64.;
    preCol.rgb += match / 3.;
    //return vec4(nearestColour(preCol * (1. + .2 * (sin(.1 * (gl_FragCoord.x + gl_FragCoord.y + time))))), 1.);
    return vec4(nearestColour(preCol), 1.);
}

void main(){
	vec4 col = texture2D(texture, vertTexCoord.xy);
	col = dither8x8(vec2(gl_FragCoord.x, gl_FragCoord.y), col);
	gl_FragColor = col;
}