perf: adaptive cloud march length

config.js

@@ -91,6 +91,18 @@ window.CONFIG = {
     // GPU bound. Read once at context creation, so a reload is needed.
     antialias: false,             // false saves GPU fill rate
 
+    // ------------------------------------------------------------------
+    // Performance
+    // ------------------------------------------------------------------
+    // Adaptive cloud raymarch: shortens the cloud march when the debug FPS
+    // drops, and lengthens it again when the scene stays comfortably fast.
+    performance: {
+        adaptiveCloudMarch: true,
+        lowFps: 24,               // reduce march below this FPS
+        highFps: 35,              // restore march above this FPS
+        minCloudMarchUnits: 45    // never shorten below this raymarch length
+    },
+
     // ------------------------------------------------------------------
     // Location
     // ------------------------------------------------------------------

vendor/clouds3d.js

@@ -1537,6 +1537,24 @@ var CLOUD_HORIZON_SOFT = CLOUD_SOFT_EDGES && (typeof window.CONFIG.clouds.horizo
     ? Math.max(0.1, Math.min(40.0, window.CONFIG.clouds.horizonSoftness)) : (CLOUD_SOFT_EDGES ? 8.0 : 0.1);
 var CLOUD_MAX_MARCH_UNITS = (window.CONFIG && typeof window.CONFIG.clouds.maxMarchUnits === 'number')
     ? Math.max(10.0, Math.min(300.0, window.CONFIG.clouds.maxMarchUnits)) : 30.0;
+var PERF_CFG = (window.CONFIG && window.CONFIG.performance) || {};
+var ADAPTIVE_CLOUD_MARCH = PERF_CFG.adaptiveCloudMarch !== false;
+var ADAPTIVE_LOW_FPS = (typeof PERF_CFG.lowFps === 'number') ? Math.max(5, PERF_CFG.lowFps) : 24;
+var ADAPTIVE_HIGH_FPS = (typeof PERF_CFG.highFps === 'number') ? Math.max(ADAPTIVE_LOW_FPS + 1, PERF_CFG.highFps) : 35;
+var CLOUD_MARCH_MIN = (typeof PERF_CFG.minCloudMarchUnits === 'number')
+    ? Math.max(10.0, Math.min(CLOUD_MAX_MARCH_UNITS, PERF_CFG.minCloudMarchUnits)) : Math.min(45.0, CLOUD_MAX_MARCH_UNITS);
+var adaptiveCloudMarchUnits = CLOUD_MAX_MARCH_UNITS;
+function updateAdaptiveCloudMarch() {
+    if (!ADAPTIVE_CLOUD_MARCH) return CLOUD_MAX_MARCH_UNITS;
+    var fps = Number(window.__fps || 0);
+    if (!fps || fps <= 0) return adaptiveCloudMarchUnits;
+    if (fps < ADAPTIVE_LOW_FPS) {
+        adaptiveCloudMarchUnits = Math.max(CLOUD_MARCH_MIN, adaptiveCloudMarchUnits - 10);
+    } else if (fps > ADAPTIVE_HIGH_FPS) {
+        adaptiveCloudMarchUnits = Math.min(CLOUD_MAX_MARCH_UNITS, adaptiveCloudMarchUnits + 5);
+    }
+    return adaptiveCloudMarchUnits;
+}
 var CLOUD_TERRAIN_OCCLUSION = !(window.CONFIG && window.CONFIG.clouds && window.CONFIG.clouds.terrainOcclusion === false);
 var CLOUD_WIND_CFG = (window.CONFIG && window.CONFIG.clouds && window.CONFIG.clouds.wind) || {};
 var CLOUD_WIND_SCALE = (typeof CLOUD_WIND_CFG.speedScale === 'number') ? Math.max(0, CLOUD_WIND_CFG.speedScale) : 80;
@@ -7418,7 +7436,7 @@ window.clouds3dRender = function(target) {
     gl.uniform1f(s.uCloudBot, CLOUD_BOT);
     gl.uniform1f(s.uCloudEdgeSoft, CLOUD_EDGE_SOFT);
     gl.uniform1f(s.uCloudHorizonSoft, CLOUD_HORIZON_SOFT);
-    gl.uniform1f(s.uCloudMaxMarch, CLOUD_MAX_MARCH_UNITS);
+    gl.uniform1f(s.uCloudMaxMarch, updateAdaptiveCloudMarch());
     gl.uniform1f(s.uCloudNearFadeStart, CLOUD_NEAR_FADE_START);
     gl.uniform1f(s.uCloudNearFadeEnd, CLOUD_NEAR_FADE_END);