perf: reduce cloud noise octaves

vendor/clouds3d.js

@@ -194,19 +194,18 @@ var FRAG_SRC = [
                 'mix(hash3(i + vec3(0,1,1)), hash3(i + vec3(1,1,1)), f.x), f.y),',
             'f.z);',
     '}',
-    // Four octaves (the name stayed): the extra high-frequency octave breaks
-    // up the iso-surfaces that made the deck read as stacked slabs. Sum is
-    // renormalised to the old 0.875 range so baseThresh still means the same
-    // cloud coverage.
+    // Three octaves: cheaper cloud noise while keeping the base coverage
+    // range near 0.875. The detail octave in cloudDensity still breaks up
+    // close silhouettes.
     'float fbm3(vec3 p) {',
         'float v = 0.0;',
         'float a = 0.5;',
-        'for (int i = 0; i < 4; i++) {',
+        'for (int i = 0; i < 3; i++) {',
             'v += a * noise3(p);',
             'p = p * 2.03 + vec3(13.7, 7.1, 19.3);',
             'a *= 0.5;',
         '}',
-        'return v * 0.93333;',
+        'return v;',
     '}',
     // Density at a point in the cloud layer. Two fBm layers: the
     // base one at low frequency gives the large puffs, the detail
@@ -826,19 +825,18 @@ var CLOUD_SAMPLER_GLSL = [
                 'mix(hash3(i + vec3(0,1,1)), hash3(i + vec3(1,1,1)), f.x), f.y),',
             'f.z);',
     '}',
-    // Four octaves (the name stayed): the extra high-frequency octave breaks
-    // up the iso-surfaces that made the deck read as stacked slabs. Sum is
-    // renormalised to the old 0.875 range so baseThresh still means the same
-    // cloud coverage.
+    // Three octaves: cheaper cloud noise while keeping the base coverage
+    // range near 0.875. The detail octave in cloudDensity still breaks up
+    // close silhouettes.
     'float fbm3(vec3 p) {',
         'float v = 0.0;',
         'float a = 0.5;',
-        'for (int i = 0; i < 4; i++) {',
+        'for (int i = 0; i < 3; i++) {',
             'v += a * noise3(p);',
             'p = p * 2.03 + vec3(13.7, 7.1, 19.3);',
             'a *= 0.5;',
         '}',
-        'return v * 0.93333;',
+        'return v;',
     '}',
     // Height field lookup on the same grid the mesh was built from, so a
     // ridge occludes exactly the ridge you can see.