atmosphere: replace flickering full-screen haze with stable terrain haze

config.js

@@ -317,7 +317,7 @@ window.CONFIG = {
         rayleighGain: 8.0,        // exposure for the physical sky term
         distanceFog: false,       // legacy aerial perspective is off
         haze: {
-            enabled: true,
+            enabled: false,       // full-screen haze pass causes horizon/sky flicker
             heightKm: 100,
             scaleHeightKm: 8.5,
             density: 0.18,
@@ -325,6 +325,14 @@ window.CONFIG = {
             gain: 1.0,
             maxAlpha: 0.55
         },
+        terrainHaze: {
+            enabled: true,
+            scaleHeightKm: 8.5,
+            density: 0.22,
+            gain: 1.0,
+            maxAlpha: 0.65,
+            color: [0.58, 0.64, 0.72]
+        },
         model: {
             enabled: false        // legacy full atmosphere model remains off
         },

vendor/clouds3d.js

@@ -688,6 +688,12 @@ var TERRAIN_FRAG_SRC = [
     'uniform vec3 uCamPos;',       // world-space camera, for the view direction
     'uniform float uEarthRadius;',
     'uniform float uCurvatureOn;',
+    'uniform float uHazeOn;',
+    'uniform float uHazeDensity;',
+    'uniform float uHazeScaleHeightUnits;',
+    'uniform float uHazeGain;',
+    'uniform float uHazeMaxAlpha;',
+    'uniform vec3 uHazeColor;',
     'uniform float uEdgeFadeTiles;',
     'uniform vec3 uWireColor;',  // non-zero -> debug wireframe overlay (flat colour)
     'varying vec3 vNormal;',
@@ -697,6 +703,21 @@ var TERRAIN_FRAG_SRC = [
     'varying vec3 vWorld;',
     'varying vec3 vColor;',
     CLOUD_SAMPLER_GLSL,
+    'float terrainHazeColumn(vec3 world) {',
+        'float dist = length(world - uCamPos);',
+        'if (dist <= 0.0) return 0.0;',
+        'if (uCurvatureOn < 0.5) return dist;',
+        'float R = max(1.0, uEarthRadius);',
+        'float Hs = max(0.05, uHazeScaleHeightUnits);',
+        'vec3 C = vec3(uCamPos.x, -R, uCamPos.z);',
+        'float column = 0.0;',
+        'for (int i = 0; i < 8; i++) {',
+            'vec3 p = mix(uCamPos, world, (float(i) + 0.5) / 8.0);',
+            'float alt = max(0.0, length(p - C) - R);',
+            'column += exp(-alt / Hs) * dist / 8.0 / Hs;',
+        '}',
+        'return column;',
+    '}',
     'void main() {',
         'vec2 gUv = vUV;',
         // Edge fade: beyond the canvas the texture is clamped to the
@@ -784,12 +805,19 @@ var TERRAIN_FRAG_SRC = [
         // veil but into the airlight itself - blue-biased (Rayleigh,
         // 1/lambda^4) and brighter towards the sun through the (1+cos^2)/2
         // phase function.
-        'float tau = uAirDensity * dist * (0.75 + 0.25 * smoothstep(0.4, 0.0, vY));',
+        'float hazeTau = 0.0;',
-        'float trans = exp(-tau);',
+        'if (uHazeOn > 0.5) {',
+            'hazeTau = uHazeDensity * terrainHazeColumn(vWorld);',
+        '} else {',
+            'hazeTau = uAirDensity * dist * (0.75 + 0.25 * smoothstep(0.4, 0.0, vY));',
+        '}',
+        'float trans = exp(-hazeTau);',
         'vec3 vd = normalize(vWorld - uCamPos);',
         'float cosT = dot(vd, uSunDir);',
         'float rphase = 0.5 + 0.5 * cosT * cosT;',
-        'col = col * trans + uAirColor * rphase * (1.0 - trans);',
+        'float hazeAlpha = clamp((1.0 - trans) * uHazeGain, 0.0, uHazeMaxAlpha);',
+        'vec3 hazeCol = mix(uHazeColor, uAirColor, 0.25) * (0.75 + 0.25 * rphase);',
+        'col = mix(col, hazeCol, hazeAlpha);',
         // Edge fade to the same horizon colour
         'col = mix(horizonCol, col, edgeFade);',
         // Wireframe overlay: when CONFIG.terrain.wireframe is set the
@@ -944,6 +972,12 @@ function init(canvas) {
     var terrainUEarthRadius = terrainProg ? gl.getUniformLocation(terrainProg, 'uEarthRadius') : null;
     var terrainUCurvatureOn = terrainProg ? gl.getUniformLocation(terrainProg, 'uCurvatureOn') : null;
     var terrainUedgeFade = terrainProg ? gl.getUniformLocation(terrainProg, 'uEdgeFadeTiles') : null;
+    var terrainUHazeOn = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeOn') : null;
+    var terrainUHazeDensity = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeDensity') : null;
+    var terrainUHazeScale = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeScaleHeightUnits') : null;
+    var terrainUHazeGain = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeGain') : null;
+    var terrainUHazeMaxAlpha = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeMaxAlpha') : null;
+    var terrainUHazeColor = terrainProg ? gl.getUniformLocation(terrainProg, 'uHazeColor') : null;
     var terrainUstarAmb = terrainProg ? gl.getUniformLocation(terrainProg, 'uStarAmb') : null;
     var terrainUtime = terrainProg ? gl.getUniformLocation(terrainProg, 'uTime') : null;
     var terrainUcloudbot = terrainProg ? gl.getUniformLocation(terrainProg, 'uCloudBot') : null;
@@ -1021,6 +1055,9 @@ function init(canvas) {
             uCamPos: terrainUcampos,
             uEarthRadius: terrainUEarthRadius, uCurvatureOn: terrainUCurvatureOn,
             uEdgeFadeTiles: terrainUedgeFade,
+            uHazeOn: terrainUHazeOn, uHazeDensity: terrainUHazeDensity,
+            uHazeScaleHeightUnits: terrainUHazeScale, uHazeGain: terrainUHazeGain,
+            uHazeMaxAlpha: terrainUHazeMaxAlpha, uHazeColor: terrainUHazeColor,
             uStarAmb: terrainUstarAmb,
             uTime: terrainUtime, uCloudBot: terrainUcloudbot,
             uCloudTop: terrainUcloudtop, uDensity: terrainUdensity,
@@ -2463,6 +2500,22 @@ 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 TERRAIN_HAZE_CFG = ATMO.terrainHaze || {};
+var TERRAIN_HAZE_ON = TERRAIN_HAZE_CFG.enabled !== false;
+var TERRAIN_HAZE_SCALE_HEIGHT_KM = (typeof TERRAIN_HAZE_CFG.scaleHeightKm === 'number')
+    ? Math.max(1.0, Math.min(30.0, TERRAIN_HAZE_CFG.scaleHeightKm)) : 8.5;
+var TERRAIN_HAZE_SCALE_HEIGHT_UNITS = TERRAIN_HAZE_SCALE_HEIGHT_KM / KM_PER_TILE;
+var TERRAIN_HAZE_DENSITY = (typeof TERRAIN_HAZE_CFG.density === 'number')
+    ? Math.max(0.01, Math.min(5.0, TERRAIN_HAZE_CFG.density)) : 0.22;
+var TERRAIN_HAZE_GAIN = (typeof TERRAIN_HAZE_CFG.gain === 'number')
+    ? Math.max(0.1, Math.min(5.0, TERRAIN_HAZE_CFG.gain)) : 1.0;
+var TERRAIN_HAZE_MAX_ALPHA = (typeof TERRAIN_HAZE_CFG.maxAlpha === 'number')
+    ? Math.max(0.05, Math.min(1.0, TERRAIN_HAZE_CFG.maxAlpha)) : 0.65;
+var TERRAIN_HAZE_COLOR = new Float32Array(
+    Array.isArray(TERRAIN_HAZE_CFG.color) && TERRAIN_HAZE_CFG.color.length >= 3
+        ? [TERRAIN_HAZE_CFG.color[0], TERRAIN_HAZE_CFG.color[1], TERRAIN_HAZE_CFG.color[2]]
+        : [0.58, 0.64, 0.72]
+);
 var CURV_CFG = (window.CONFIG && window.CONFIG.curvature) || {};
 var CURVATURE_ON = CURV_CFG.enabled !== false;
 var CURV_EXAG = (typeof CURV_CFG.exaggeration === 'number')
@@ -5845,6 +5898,12 @@ window.clouds3dRender = function(target) {
         gl.uniform1f(terr.uEarthRadius, EARTH_RADIUS_UNITS);
         gl.uniform1f(terr.uCurvatureOn, CURVATURE_ON ? 1.0 : 0.0);
         gl.uniform1f(terr.uEdgeFadeTiles, EDGE_FADE_TILES);
+        gl.uniform1f(terr.uHazeOn, TERRAIN_HAZE_ON ? 1.0 : 0.0);
+        gl.uniform1f(terr.uHazeDensity, TERRAIN_HAZE_DENSITY);
+        gl.uniform1f(terr.uHazeScaleHeightUnits, TERRAIN_HAZE_SCALE_HEIGHT_UNITS);
+        gl.uniform1f(terr.uHazeGain, TERRAIN_HAZE_GAIN);
+        gl.uniform1f(terr.uHazeMaxAlpha, TERRAIN_HAZE_MAX_ALPHA);
+        gl.uniform3f(terr.uHazeColor, TERRAIN_HAZE_COLOR[0], TERRAIN_HAZE_COLOR[1], TERRAIN_HAZE_COLOR[2]);
 
         gl.bindBuffer(gl.ARRAY_BUFFER, terr.vbo);
         var STRIDE = 11 * 4; // 11 floats per vertex