dithered skybox

assets/4096_bayer_skyboxfill.frag

@@ -0,0 +1,58 @@
+varying vec4 v_color;
+varying vec2 v_texCoords;
+uniform sampler2D u_texture;
+
+
+uniform vec3 topColor;
+uniform vec3 bottomColor;
+uniform float screenHeight;
+
+
+// "steps" of R, G and B. Must be integer && equal or greater than 2
+uniform float rcount = 256.0; // it even works on 256.0!
+uniform float gcount = 256.0;
+uniform float bcount = 256.0;
+
+
+
+int bayer[8][8] = {
+{ 0,32, 8,40, 2,34,10,42}, // 8x8 bayer ordered dithering
+{48,16,56,24,50,18,58,26}, // pattern. Each input pixel
+{12,44, 4,36,14,46, 6,38}, // is scaled to the 0..63 range
+{60,28,52,20,62,30,54,22}, // before looking in this table
+{ 3,35,11,43, 1,33, 9,41}, // to determine the action
+{51,19,59,27,49,17,57,25},
+{15,47, 7,39,13,45, 5,37},
+{63,31,55,23,61,29,53,21} }; // fun fact: you can calculate bayer value on-the-fly but LUT is faster
+float bayerSize = 8.0;
+float bayerDivider = bayerSize * bayerSize;
+
+
+vec4 nearestColour(vec4 incolor) {
+    vec4 rgbaCounts = vec4(rcount, gcount, bcount, 1.0);
+
+
+    vec4 color = incolor;
+
+    color.r = floor((rgbaCounts.r - 1.0) * color.r + 0.5) / (rgbaCounts.r - 1.0);
+    color.g = floor((rgbaCounts.g - 1.0) * color.g + 0.5) / (rgbaCounts.g - 1.0);
+    color.b = floor((rgbaCounts.b - 1.0) * color.b + 0.5) / (rgbaCounts.b - 1.0);
+    color.a = 1.0;
+
+    return color;
+}
+
+void main(void) {
+    float spread = 1.0 / (0.299 * (rcount - 1.0) + 0.587 * (gcount - 1.0) + 0.114 * (bcount - 1.0));  // this spread value is optimised one -- try your own values for various effects!
+
+    float scale = v_texCoords.y; // screenHeight;
+    float inR = mix(bottomColor.r, topColor.r, scale);
+    float inG = mix(bottomColor.g, topColor.g, scale);
+    float inB = mix(bottomColor.b, topColor.b, scale);
+
+    vec4 inColor = vec4(inR, inG, inB, 1.0);
+
+    vec2 entry = mod(gl_FragCoord.xy, vec2(bayerSize, bayerSize));
+
+    gl_FragColor = nearestColour(inColor + spread * (bayer[int(entry.y)][int(entry.x)] / bayerDivider - 0.5));
+}