From a06f7038d8216bd571caec024ac29c49eba124cf Mon Sep 17 00:00:00 2001
From: Richard Zink <Richard Zink>
Date: Mon, 12 Oct 2026 15:13:26 +0200
Subject: [PATCH] atmosphere: make Rayleigh sky follow spherical Earth radius

---
 vendor/clouds3d.js | 51 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 48 insertions(+), 3 deletions(-)

diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index 51c3595..2860b80 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -257,6 +257,51 @@ var FRAG_SRC = [
         'if (r.y > 0.0) m = max(m, r.y);',
         'return m;',
     '}',
+    'vec3 sphericalRayleighTau(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 uRayleighBeta * mView;',
+        '}',
+        'float R = max(1.0, uEarthRadius);',
+        'float H = max(1.0, uAtmoHeightUnits);',
+        'float Hs = max(0.05, uAtmoScaleHeightUnits);',
+        '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 vec3(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 uRayleighBeta * column;',
+    '}',
     // Two modes driven by uMode:
     //   0 = SKY:    full-screen pass that paints the sky gradient and
     //                stars into the framebuffer (opaque, alpha = 1).
@@ -345,9 +390,7 @@ var FRAG_SRC = [
                 'float phase = 0.5 + 0.5 * cosT * cosT;',
                 'float sunUp = smoothstep(-0.25, 0.05, uSunAlt);',
                 'vec3 sunTop = uSunColor * uSunInt * sunUp;',
-                'float viewY = max(rd.y, 0.0);',
-                'float mView = (viewY > 0.02) ? min(38.0, 1.0 / viewY) : 38.0;',
-                'vec3 tauView = uRayleighBeta * mView;',
+                'vec3 tauView = sphericalRayleighTau(rd);',
                 'vec3 single = phase * sunTop * (1.0 - exp(-tauView));',
                 'vec3 multi = phase * sunTop * tauView * tauView * 0.12;',
                 'vec3 ambient = max(vec3(uSkyAmb), uStarAmb * vec3(0.7, 0.85, 1.0)) *',
@@ -5661,6 +5704,8 @@ window.clouds3dRender = function(target) {
     gl.enableVertexAttribArray(s.aPos);
     gl.vertexAttribPointer(s.aPos, 2, gl.FLOAT, false, 0, 0);
     gl.uniformMatrix4fv(s.uViewProjInv, false, viewProjInv);
+    gl.uniform3f(s.uCamPos, camX, camY, camZ);
+    gl.uniform1f(s.uCurvatureOn, CURVATURE_ON ? 1.0 : 0.0);
     gl.disable(gl.DEPTH_TEST);
     gl.depthMask(false);
     gl.uniform1i(s.uMode, 0);