atmosphere: cap haze alpha to avoid hard horizon cut

config.js

@@ -320,9 +320,10 @@ window.CONFIG = {
             enabled: true,
             heightKm: 60,
             scaleHeightKm: 8.5,
-            density: 0.25,
+            density: 0.18,
             grayTau: 1.2,
-            gain: 1.0
+            gain: 1.0,
+            maxAlpha: 0.55
         },
         model: {
             enabled: false        // legacy full atmosphere model remains off

vendor/clouds3d.js

@@ -92,6 +92,7 @@ var FRAG_SRC = [
     'uniform float uAtmoDensity;',
     'uniform float uAtmoGrayTau;',
     'uniform float uAtmoGain;',
+    'uniform float uAtmoMaxAlpha;',
     'uniform float uEarthRadius;',
     'uniform float uCurvatureOn;',
     'uniform vec3 uCamPos;',
@@ -374,8 +375,9 @@ var FRAG_SRC = [
                 'tau += dtau;',
                 't += step;',
             '}',
-            'float alpha = clamp(1.0 - exp(-tau), 0.0, 1.0);',
+            'float rawAlpha = clamp(1.0 - exp(-tau), 0.0, 1.0);',
-            'vec3 col = scatter / max(alpha, 1e-4) * uAtmoGain;',
+            'float alpha = clamp(rawAlpha * uAtmoGain, 0.0, uAtmoMaxAlpha);',
+            'vec3 col = scatter / max(rawAlpha, 1e-4);',
             'gl_FragColor = vec4(col, alpha);',
             'return;',
         '}',
@@ -859,6 +861,7 @@ function init(canvas) {
     var uAtmoDensity = gl.getUniformLocation(prog, 'uAtmoDensity');
     var uAtmoGrayTau = gl.getUniformLocation(prog, 'uAtmoGrayTau');
     var uAtmoGain = gl.getUniformLocation(prog, 'uAtmoGain');
+    var uAtmoMaxAlpha = gl.getUniformLocation(prog, 'uAtmoMaxAlpha');
     var uEarthRadius = gl.getUniformLocation(prog, 'uEarthRadius');
     var uCurvatureOn = gl.getUniformLocation(prog, 'uCurvatureOn');
     var uCamPos = gl.getUniformLocation(prog, 'uCamPos');
@@ -982,6 +985,7 @@ function init(canvas) {
         uAtmoModelOn: uAtmoModelOn, uAtmoHeightUnits: uAtmoHeightUnits,
         uAtmoScaleHeightUnits: uAtmoScaleHeightUnits, uAtmoDensity: uAtmoDensity,
         uAtmoGrayTau: uAtmoGrayTau, uAtmoGain: uAtmoGain,
+        uAtmoMaxAlpha: uAtmoMaxAlpha,
         uEarthRadius: uEarthRadius,
         uCurvatureOn: uCurvatureOn, uCamPos: uCamPos,
         uAtmoBlueColor: uAtmoBlueColor, uAtmoGrayColor: uAtmoGrayColor,
@@ -2453,6 +2457,10 @@ var ATMO_MODEL_GAIN = (typeof HAZE_CFG.gain === 'number')
     ? Math.max(0.1, Math.min(5.0, HAZE_CFG.gain))
     : ((typeof ATMO_MODEL.gain === 'number')
         ? Math.max(0.1, Math.min(5.0, ATMO_MODEL.gain)) : 1.0);
+var ATMO_MODEL_MAX_ALPHA = (typeof HAZE_CFG.maxAlpha === 'number')
+    ? Math.max(0.05, Math.min(1.0, HAZE_CFG.maxAlpha))
+    : ((typeof ATMO_MODEL.maxAlpha === 'number')
+        ? Math.max(0.05, Math.min(1.0, ATMO_MODEL.maxAlpha)) : 0.55);
 var CURV_CFG = (window.CONFIG && window.CONFIG.curvature) || {};
 var CURVATURE_ON = CURV_CFG.enabled !== false;
 var CURV_EXAG = (typeof CURV_CFG.exaggeration === 'number')
@@ -5556,6 +5564,7 @@ window.clouds3dRender = function(target) {
     gl.uniform1f(s.uAtmoDensity, ATMO_MODEL_DENSITY);
     gl.uniform1f(s.uAtmoGrayTau, ATMO_MODEL_GRAY_TAU);
     gl.uniform1f(s.uAtmoGain, ATMO_MODEL_GAIN);
+    gl.uniform1f(s.uAtmoMaxAlpha, ATMO_MODEL_MAX_ALPHA);
     gl.uniform1f(s.uEarthRadius, EARTH_RADIUS_UNITS);
     gl.uniform3fv(s.uAtmoBlueColor, ATMO_MODEL_BLUE_COLOR);
     gl.uniform3fv(s.uAtmoGrayColor, ATMO_MODEL_GRAY_COLOR);