atmosphere: add stable air haze behind terrain

config.js

@@ -333,6 +333,14 @@ window.CONFIG = {
             maxAlpha: 0.65,
             color: [0.58, 0.64, 0.72]
         },
+        airHaze: {
+            enabled: true,
+            scaleHeightKm: 8.5,
+            density: 0.16,
+            gain: 1.0,
+            maxAlpha: 0.45,
+            color: [0.58, 0.64, 0.72]
+        },
         model: {
             enabled: false        // legacy full atmosphere model remains off
         },

vendor/clouds3d.js

@@ -110,6 +110,12 @@ var FRAG_SRC = [
     'uniform float uSunAirMass;',  // relative air mass of the sun beam
     'uniform float uRayleighGain;',
     'uniform float uPhysicalSkyOn;',
+    'uniform float uAirHazeOn;',
+    'uniform float uAirHazeDensity;',
+    'uniform float uAirHazeScaleHeightUnits;',
+    'uniform float uAirHazeGain;',
+    'uniform float uAirHazeMaxAlpha;',
+    'uniform vec3 uAirHazeColor;',
     'uniform vec3 uCloudAlbedo;',  // theme-tinted but brightness-normalised
     'uniform float uAirDensity;',  // slant optical depth per world unit
     'uniform float uCloudHaze;',   // clouds sit above most of the haze: much weaker
@@ -303,6 +309,51 @@ var FRAG_SRC = [
         '}',
         'return uRayleighBeta * column;',
     '}',
+    'float airHazeColumn(vec3 rd) {',
+        'if (uCurvatureOn < 0.5) {',
+            'float viewY = max(rd.y, 0.0);',
+            'float mView = (viewY > 0.02) ? min(38.0, 1.0 / viewY) : 38.0;',
+            'return mView;',
+        '}',
+        'float R = max(1.0, uEarthRadius);',
+        'float H = max(1.0, uAtmoHeightUnits);',
+        'float Hs = max(0.05, uAirHazeScaleHeightUnits);',
+        'vec3 C = vec3(uCamPos.x, -R, uCamPos.z);',
+        'vec3 oc = uCamPos - C;',
+        'float b = dot(oc, rd);',
+        'float rOut = R + H;',
+        'float cOut = dot(oc, oc) - rOut * rOut;',
+        'float tStart = 0.0;',
+        'float tEnd = 100.0;',
+        'float discOut = b * b - cOut;',
+        'if (discOut > 0.0) {',
+            'float sq = sqrt(discOut);',
+            'float t1 = -b - sq;',
+            'float t2 = -b + sq;',
+            'if (cOut > 0.0) tStart = max(0.0, t1);',
+            'tEnd = max(0.0, t2);',
+        '}',
+        'float cIn = dot(oc, oc) - R * R;',
+        'float discIn = b * b - cIn;',
+        'if (discIn > 0.0) {',
+            'float sq = sqrt(discIn);',
+            'float t1 = -b - sq;',
+            'float t2 = -b + sq;',
+            'if (t1 > 0.0) tEnd = min(tEnd, t1);',
+            'else if (t2 > 0.0) tEnd = min(tEnd, t2);',
+        '}',
+        'if (tEnd <= tStart) return 0.0;',
+        'float step = (tEnd - tStart) / 16.0;',
+        'float t = tStart + step * 0.5;',
+        'float column = 0.0;',
+        'for (int i = 0; i < 16; i++) {',
+            'vec3 p = uCamPos + rd * t;',
+            'float alt = max(0.0, length(p - C) - R);',
+            'column += exp(-alt / Hs) * step / Hs;',
+            't += step;',
+        '}',
+        'return column;',
+    '}',
     // Two modes driven by uMode:
     //   0 = SKY:    full-screen pass that paints the sky gradient and
     //                stars into the framebuffer (opaque, alpha = 1).
@@ -402,6 +453,12 @@ var FRAG_SRC = [
                 'vec3 phys = (single + multi + ambient) * uRayleighGain;',
                 'col = mix(col, phys, 0.82);',
             '}',
+            'if (uAirHazeOn > 0.5) {',
+                'float hazeColumn = airHazeColumn(rd);',
+                'float hazeTau = uAirHazeDensity * hazeColumn;',
+                'float hazeAlpha = clamp((1.0 - exp(-hazeTau)) * uAirHazeGain, 0.0, uAirHazeMaxAlpha);',
+                'col = mix(col, uAirHazeColor, hazeAlpha);',
+            '}',
             'float nightFactor = 1.0 - smoothstep(-0.15, 0.05, uSunAlt);',
             'float skyMask = smoothstep(-0.20, 0.40, rd.y);',
             // Stars must not sit on the moon: the disc is opaque, so every
@@ -924,6 +981,12 @@ function init(canvas) {
     var uSunAirMass = gl.getUniformLocation(prog, 'uSunAirMass');
     var uRayleighGain = gl.getUniformLocation(prog, 'uRayleighGain');
     var uPhysicalSkyOn = gl.getUniformLocation(prog, 'uPhysicalSkyOn');
+    var uAirHazeOn = gl.getUniformLocation(prog, 'uAirHazeOn');
+    var uAirHazeDensity = gl.getUniformLocation(prog, 'uAirHazeDensity');
+    var uAirHazeScaleHeightUnits = gl.getUniformLocation(prog, 'uAirHazeScaleHeightUnits');
+    var uAirHazeGain = gl.getUniformLocation(prog, 'uAirHazeGain');
+    var uAirHazeMaxAlpha = gl.getUniformLocation(prog, 'uAirHazeMaxAlpha');
+    var uAirHazeColor = gl.getUniformLocation(prog, 'uAirHazeColor');
     var uCloudAlbedo = gl.getUniformLocation(prog, 'uCloudAlbedo');
     var uAirDensity = gl.getUniformLocation(prog, 'uAirDensity');
     var uCloudHaze = gl.getUniformLocation(prog, 'uCloudHaze');
@@ -1029,7 +1092,11 @@ function init(canvas) {
         uMoonInt: uMoonInt, uSkyAmb: uSkyAmb, uStarAmb: uStarAmb,
         uPhysical: uPhysical, uAirColor: uAirColor,
         uRayleighBeta: uRayleighBeta, uSunAirMass: uSunAirMass,
-        uRayleighGain: uRayleighGain, uPhysicalSkyOn: uPhysicalSkyOn, uCloudAlbedo: uCloudAlbedo,
+        uRayleighGain: uRayleighGain, uPhysicalSkyOn: uPhysicalSkyOn,
+        uAirHazeOn: uAirHazeOn, uAirHazeDensity: uAirHazeDensity,
+        uAirHazeScaleHeightUnits: uAirHazeScaleHeightUnits,
+        uAirHazeGain: uAirHazeGain, uAirHazeMaxAlpha: uAirHazeMaxAlpha,
+        uAirHazeColor: uAirHazeColor, uCloudAlbedo: uCloudAlbedo,
         uAirDensity: uAirDensity, uCloudHaze: uCloudHaze,
         uSkyTex: uSkyTex, uSkyOn: uSkyOn, uStarLon: uStarLon, uPole: uPole,
         uMoonTex: uMoonTex, uMoonTexOn: uMoonTexOn, uMoonR: uMoonR,
@@ -2516,6 +2583,24 @@ var TERRAIN_HAZE_COLOR = new Float32Array(
         ? [TERRAIN_HAZE_CFG.color[0], TERRAIN_HAZE_CFG.color[1], TERRAIN_HAZE_CFG.color[2]]
         : [0.58, 0.64, 0.72]
 );
+var AIR_HAZE_CFG = ATMO.airHaze || TERRAIN_HAZE_CFG || {};
+var AIR_HAZE_ON = (typeof AIR_HAZE_CFG.enabled === 'boolean')
+    ? AIR_HAZE_CFG.enabled
+    : (TERRAIN_HAZE_ON && AIR_HAZE_CFG.enabled !== false);
+var AIR_HAZE_SCALE_HEIGHT_KM = (typeof AIR_HAZE_CFG.scaleHeightKm === 'number')
+    ? Math.max(1.0, Math.min(30.0, AIR_HAZE_CFG.scaleHeightKm)) : 8.5;
+var AIR_HAZE_SCALE_HEIGHT_UNITS = AIR_HAZE_SCALE_HEIGHT_KM / KM_PER_TILE;
+var AIR_HAZE_DENSITY = (typeof AIR_HAZE_CFG.density === 'number')
+    ? Math.max(0.01, Math.min(5.0, AIR_HAZE_CFG.density)) : 0.16;
+var AIR_HAZE_GAIN = (typeof AIR_HAZE_CFG.gain === 'number')
+    ? Math.max(0.1, Math.min(5.0, AIR_HAZE_CFG.gain)) : 1.0;
+var AIR_HAZE_MAX_ALPHA = (typeof AIR_HAZE_CFG.maxAlpha === 'number')
+    ? Math.max(0.05, Math.min(1.0, AIR_HAZE_CFG.maxAlpha)) : 0.45;
+var AIR_HAZE_COLOR = new Float32Array(
+    Array.isArray(AIR_HAZE_CFG.color) && AIR_HAZE_CFG.color.length >= 3
+        ? [AIR_HAZE_CFG.color[0], AIR_HAZE_CFG.color[1], AIR_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')
@@ -5608,6 +5693,12 @@ window.clouds3dRender = function(target) {
     gl.uniform1f(s.uSunAirMass, airMass(Math.max(sunAlt, 0.0)));
     gl.uniform1f(s.uRayleighGain, ATMO_RAYLEIGH_GAIN);
     gl.uniform1f(s.uPhysicalSkyOn, ATMO_PHYSICAL_SKY ? 1.0 : 0.0);
+    gl.uniform1f(s.uAirHazeOn, AIR_HAZE_ON ? 1.0 : 0.0);
+    gl.uniform1f(s.uAirHazeDensity, AIR_HAZE_DENSITY);
+    gl.uniform1f(s.uAirHazeScaleHeightUnits, AIR_HAZE_SCALE_HEIGHT_UNITS);
+    gl.uniform1f(s.uAirHazeGain, AIR_HAZE_GAIN);
+    gl.uniform1f(s.uAirHazeMaxAlpha, AIR_HAZE_MAX_ALPHA);
+    gl.uniform3f(s.uAirHazeColor, AIR_HAZE_COLOR[0], AIR_HAZE_COLOR[1], AIR_HAZE_COLOR[2]);
     gl.uniform3f(s.uSunColor, _beam[0], _beam[1], _beam[2]);
     gl.uniform1f(s.uSunInt, _beamL);
     gl.uniform3f(s.uMoonColor, _mBeam[0], _mBeam[1], _mBeam[2]);