atmosphere: apply haze to terrain rays that hit elevated terrain

vendor/clouds3d.js

@@ -358,6 +358,7 @@ var FRAG_SRC = [
             'float step = (tEnd - tStart) / 32.0;',
             'float t = tStart + step * 0.5;',
             'float tau = 0.0;',
+            'float hitsTerrain = hitsInner;',
             'vec3 scatter = vec3(0.0);',
             'float cosTA = dot(rd, uSunDir);',
             'float cosTM = dot(rd, uMoonDir);',
@@ -366,6 +367,7 @@ var FRAG_SRC = [
             'for (int i = 0; i < 32; i++) {',
                 'vec3 p = ro + rd * t;',
                 'float alt = max(0.0, length(p - C) - R);',
+                'if (uElevOn > 0.5 && alt < terrElev(p.xz) * uElevScale) hitsTerrain = 1.0;',
                 'float dens = exp(-alt / Hs) / Hs;',
                 'float dtau = uAtmoDensity * dens * step;',
                 'float transBefore = exp(-tau);',
@@ -376,7 +378,7 @@ var FRAG_SRC = [
                 't += step;',
             '}',
             'float rawAlpha = clamp(1.0 - exp(-tau), 0.0, 1.0);',
-            'float alpha = clamp(rawAlpha * uAtmoGain * hitsInner, 0.0, uAtmoMaxAlpha);',
+            'float alpha = clamp(rawAlpha * uAtmoGain * hitsTerrain, 0.0, uAtmoMaxAlpha);',
             'vec3 col = scatter / max(rawAlpha, 1e-4);',
             'gl_FragColor = vec4(col, alpha);',
             'return;',