Remove colour banding

CHANGELOG.md

@@ -43,6 +43,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added arthropods
 - A 'point light glow' effect, making lanterns and other point lights more visually pronounced
 - Generate random name for site2 sites
+- Shader dithering to remove banding from scenes with large colour gradients
 
 ### Changed
 

assets/voxygen/shaders/include/random.glsl

@@ -10,9 +10,9 @@ float hash(vec4 p) {
     return (fract(p.x * p.y * (1.0 - p.z) * p.w * (p.x + p.y + p.z + p.w)) - 0.5) * 2.0;
 }
 
-#define M1 1597334677U  //1719413*929
-#define M2 3812015801U  //140473*2467*11
-#define M3 2741598923U
+#define M1 2047667443U
+#define M2 3883706873U
+#define M3 3961281721U
 
 float hash_one(uint q) {
     uint n = ((M3 * q) ^ M2) * M1;
@@ -20,6 +20,13 @@ float hash_one(uint q) {
     return float(n) * (1.0 / float(0xffffffffU));
 }
 
+float hash_two(uvec2 q) {
+    q *= uvec2(M1, M2);
+    uint n = q.x ^ q.y;
+    n = n * (n ^ (n >> 15));
+    return float(n) * (1.0 / float(0xffffffffU));
+}
+
 float hash_fast(uvec3 q) {
     q *= uvec3(M1, M2, M3);
 

assets/voxygen/shaders/postprocess-frag.glsl

@@ -197,15 +197,15 @@ void main() {
     //     return;
     // }
 
+    vec2 sample_uv = uv;
     #ifdef EXPERIMENTAL_UNDERWARPER
-        vec2 uv = uv;
         if (medium.x == MEDIUM_WATER) {
-            uv += sin(uv.yx * 40 + tick.xx * 1.0) * 0.003;
+            sample_uv += sin(uv.yx * 40 + tick.xx * 1.0) * 0.003;
         }
     #endif
 
-    vec4 aa_color = aa_apply(t_src_color, s_src_color, uv * screen_res.xy, screen_res.xy);
-   
+    vec4 aa_color = aa_apply(t_src_color, s_src_color, sample_uv * screen_res.xy, screen_res.xy);
+
     #ifdef EXPERIMENTAL_SOBEL
         vec3 s[8];
         s[0] = aa_sample(uv, vec2(-1,  1));
@@ -282,5 +282,9 @@ void main() {
     }
 #endif
 
+    // Add a small amount of very cheap dithering noise to remove banding from gradients
+    // TODO: Instead of 256, detect the colour resolution of the display
+    final_color.rgb = max(vec3(0), final_color.rgb - hash_two(uvec2(uv * screen_res.xy)) / 256.0);
+
     tgt_color = vec4(final_color.rgb, 1);
 }