clouds: use real terrain height for cloud occlusion

vendor/clouds3d.js

@@ -79,6 +79,7 @@ var FRAG_SRC = [
     '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)
+    'uniform float uTerrainExag;', // terrain vertical exaggeration
     'uniform vec3 uSunDir;',       // unit vector towards the sun (world X,Y,Z)
     'uniform vec3 uMoonDir;',      // unit vector towards the moon (world X,Y,Z)
     'uniform sampler2D uSkyTex;',  // baked star catalogue + Milky Way (equirect)
@@ -675,7 +676,7 @@ var FRAG_SRC = [
                     'float distNorm = (distTex.r * 65536.0 + distTex.g * 256.0 + distTex.b) / 16777215.0;',
                     'float dist = distNorm * max(1.0, uFarPlane);',
                     'vec3 pT = uCamPos + rd * dist;',
-                    'float terrainAlt = pT.y + earthDrop(pT.xz);',
+                    'float terrainAlt = (pT.y + earthDrop(pT.xz)) / max(1.0, uTerrainExag);',
                     'if (terrainAlt > uCloudTop + 0.05) { gl_FragColor = vec4(0.0); return; }',
                 '}',
             '}',
@@ -1103,6 +1104,7 @@ function init(canvas) {
     var uElev = gl.getUniformLocation(prog, 'uElev');
     var uElevOn = gl.getUniformLocation(prog, 'uElevOn');
     var uElevScale = gl.getUniformLocation(prog, 'uElevScale');
+    var uTerrainExag = gl.getUniformLocation(prog, 'uTerrainExag');
     var uSunDir = gl.getUniformLocation(prog, 'uSunDir');
     var uMoonDir = gl.getUniformLocation(prog, 'uMoonDir');
     var uMode = gl.getUniformLocation(prog, 'uMode');
@@ -1255,7 +1257,7 @@ function init(canvas) {
         uSpeed: uSpeed, uDensity: uDensity, uDayProgress: uDayProgress,
         uSunAlt: uSunAlt,
         uCloudTop: uCloudTop, uCloudBot: uCloudBot,
-        uElev: uElev, uElevOn: uElevOn, uElevScale: uElevScale,
+        uElev: uElev, uElevOn: uElevOn, uElevScale: uElevScale, uTerrainExag: uTerrainExag,
         uSunDir: uSunDir, uMoonDir: uMoonDir, uMode: uMode,
         uAtmoModelOn: uAtmoModelOn, uAtmoHeightUnits: uAtmoHeightUnits,
         uAtmoScaleHeightUnits: uAtmoScaleHeightUnits, uAtmoDensity: uAtmoDensity,
@@ -5834,6 +5836,7 @@ window.clouds3dRender = function(target) {
     gl.uniform1i(s.uElev, 2);
     gl.uniform1f(s.uElevOn, (elevTexture && TERRAIN_ON > 0.5) ? 1.0 : 0.0);
     gl.uniform1f(s.uElevScale, ELEV_SCALE_UNITS);
+    gl.uniform1f(s.uTerrainExag, TERRAIN_EXAG);
     var sd = window.__currentSunDir || [0, 0.7, 0.7];
     gl.uniform3f(s.uSunDir, sd[0], sd[1], sd[2]);
     var md = window.__currentMoonDir || sd;