[Add] Implement tileable and pile-corrected clouds.

assets/shaders/cloud.frag

@@ -24,6 +24,10 @@ void main() {
   float diffuse = max(dot(normal, -u_LightDir), 0.0);
   vec3 cloudColor = vec3(1.0) * (diffuse * 0.5 + 0.5); /* Add some ambient light. */
 
+  /* Fade out clouds at the poles to hide pinching. */
+  float poleFade = 1.0 - abs(TexCoords.y);
+  cloudAlpha *= smoothstep(0.0, 0.2, poleFade);
+
   /* Cloud colour is white. it's transparency is determined by alpha. */
   FragColor = vec4(cloudColor, cloudAlpha);
 }

src/graphics/renderer.cpp

@@ -226,7 +226,18 @@ unsigned int Renderer::_generate_cloud_texture(void) {
 
   for(int y = 0; y < height; y++) {
     for(int x = 0; x < width; x++) {
-      float noise_val = noise.GetNoise((float)x, (float)y);
+      const float R = 1.0f; /* Major radius of the torus. */
+      const float r = 0.5f; /* Minor radius of the torus. */
+
+      float u = (float)x / width  * 2.0f * M_PI;
+      float v = (float)y / height * 2.0f * M_PI;
+
+      float nx = (R + r * cos(v)) * cos(u);
+      float ny = (R + r * cos(v)) * sin(u);
+      float nz = r * sin(v);
+
+      const float noise_scale = 45.0f;
+      float noise_val = noise.GetNoise(nx * noise_scale, ny * noise_scale, nz * noise_scale);
       buffer[y*width+x] = (noise_val + 1.0f) / 2.0f;
     }
   }