fix: soften cloud march edge

config.js

@@ -335,6 +335,10 @@ window.CONFIG = {
             start: 0.35,          // world units: clouds fade out very close to camera
             end: 2.5              // full density from this distance onward
         },
+        // Maximum raymarch length through the cloud deck, in world units.
+        // Too small creates a hard cloud-deck edge/ring near the horizon.
+        maxMarchUnits: 120,       // 30 was the old fixed cap
+        // maxMarchUnits: 60       // cheaper, but a harder far edge
         // Far softening reduces detail/noise at long view distances. Lower
         // max keeps the deck denser near the horizon and can remove the
         // transparent ring around the terrain edge.

vendor/clouds3d.js

@@ -90,6 +90,7 @@ var FRAG_SRC = [
     'uniform float uCloudFarSoftStart;',
     'uniform float uCloudFarSoftEnd;',
     'uniform float uCloudFarSoftMax;',
+    'uniform float uCloudMaxMarch;',
     'uniform sampler2D uElev;',    // terrarium RGB height grid, same UV as uGround
     'uniform float uElevOn;',      // terrain enabled (0/1)
     'uniform float uElevScale;',   // metres -> world units (incl. exaggeration)
@@ -709,9 +710,9 @@ var FRAG_SRC = [
                     'tExit = min(tExit, dist - 0.02);',
                 '}',
             '}',
-            'tExit = min(tExit, tEnter + 30.0);',
+            'tExit = min(tExit, tEnter + max(1.0, uCloudMaxMarch));',
             'if (tExit <= tEnter) { gl_FragColor = vec4(0.0); return; }',
-            'float stepSize = (tExit - tEnter) / 24.0;',
+            'float stepSize = (tExit - tEnter) / 32.0;',
             'float t = tEnter + stepSize * 0.5;',
             'float coverage = clamp(uDensity, 0.0, 1.0);',
             'float baseThresh = mix(0.62, 0.20, coverage);',
@@ -721,7 +722,7 @@ var FRAG_SRC = [
             'float phase = 0.30 + 0.70 * pow(max(0.0, cosT), 2.5);',
             'float trans = 1.0;',
             'vec3 cloudSum = vec3(0.0);',
-            'for (int i = 0; i < 24; i++) {',
+            'for (int i = 0; i < 32; i++) {',
                 'vec3 p = uCamPos + rd * t;',
                 'p += rd * (ign(gl_FragCoord.xy + vec2(float(i) * 7.13, float(i) * 3.71)) - 0.5) * stepSize * 0.25;',
                 'float alt = p.y + earthDrop(p.xz);',
@@ -737,7 +738,8 @@ var FRAG_SRC = [
                     'vec3 moonC = albC * uMoonColor * (0.35 + 0.65 * max(0.0, dot(rd, uMoonDir))) * uMoonInt * 3.0;',
                     'vec3 cloudCol = direct + ambC + moonC;',
                     'float nearFade = smoothstep(uCloudNearFadeStart, uCloudNearFadeEnd, t);',
-                    'float alpha = clamp(d * stepSize * 3.50 * densityGain * nearFade, 0.0, 1.0);',
+                    'float marchFade = 1.0 - smoothstep(uCloudMaxMarch * 0.70, uCloudMaxMarch, t - tEnter);',
+                    'float alpha = clamp(d * stepSize * 3.50 * densityGain * nearFade * marchFade, 0.0, 1.0);',
                     'cloudSum += cloudCol * alpha * trans;',
                     'trans *= (1.0 - alpha);',
                     'if (trans < 0.04) break;',
@@ -1316,6 +1318,7 @@ function init(canvas) {
         uCloudFarSoftStart: gl.getUniformLocation(prog, 'uCloudFarSoftStart'),
         uCloudFarSoftEnd: gl.getUniformLocation(prog, 'uCloudFarSoftEnd'),
         uCloudFarSoftMax: gl.getUniformLocation(prog, 'uCloudFarSoftMax'),
+        uCloudMaxMarch: gl.getUniformLocation(prog, 'uCloudMaxMarch'),
         uElev: uElev, uElevOn: uElevOn, uElevScale: uElevScale, uTerrainExag: uTerrainExag,
         uSunDir: uSunDir, uMoonDir: uMoonDir, uMode: uMode,
         uAtmoModelOn: uAtmoModelOn, uAtmoHeightUnits: uAtmoHeightUnits,
@@ -1509,6 +1512,8 @@ CLOUD_TOP = Math.max(0.2, Math.min(CLOUD_TOP, 2.0));
 CLOUD_BOT = Math.min(CLOUD_BOT, CLOUD_TOP - 0.4);
 var CLOUD_NEAR_FADE_CFG = (window.CONFIG && window.CONFIG.clouds && window.CONFIG.clouds.nearFade) || {};
 var CLOUD_FAR_SOFT_CFG = (window.CONFIG && window.CONFIG.clouds && window.CONFIG.clouds.farSoft) || {};
+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 CLOUD_NEAR_FADE_START = (typeof CLOUD_NEAR_FADE_CFG.start === 'number') ? Math.max(0, CLOUD_NEAR_FADE_CFG.start) : 0.35;
 var CLOUD_NEAR_FADE_END = Math.max(CLOUD_NEAR_FADE_START + 0.1, (typeof CLOUD_NEAR_FADE_CFG.end === 'number') ? CLOUD_NEAR_FADE_CFG.end : 2.5);
 var CLOUD_FAR_SOFT_START = (typeof CLOUD_FAR_SOFT_CFG.start === 'number')
@@ -7406,6 +7411,7 @@ window.clouds3dRender = function(target) {
     gl.uniform1f(s.uCloudFarSoftStart, CLOUD_FAR_SOFT_START);
     gl.uniform1f(s.uCloudFarSoftEnd, CLOUD_FAR_SOFT_END);
     gl.uniform1f(s.uCloudFarSoftMax, CLOUD_FAR_SOFT_MAX);
+    gl.uniform1f(s.uCloudMaxMarch, CLOUD_MAX_MARCH_UNITS);
 
     // Ground mosaic uniforms + periodic re-fetch trigger.
     // uGroundCenter is the world position (X, Z) of the centre tile's