From e78c6e86b6baa58f5af3572471dbae6f94e13819 Mon Sep 17 00:00:00 2001
From: Richard Zink <Richard Zink>
Date: Mon, 12 Oct 2026 14:04:29 +0200
Subject: [PATCH] curvature: bend terrain vertices to a spherical Earth

---
 vendor/clouds3d.js | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index e12556a..fa11db5 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -530,17 +530,30 @@ var TERRAIN_VERT_SRC = [
     'attribute vec2 aUV;',
     'uniform mat4 uView;',
     'uniform mat4 uProj;',
+    'uniform vec3 uCamPos;',
+    'uniform float uEarthRadius;',
+    'uniform float uCurvatureOn;',
     'varying vec3 vNormal;',
     'varying vec2 vUV;',
     'varying float vY;',
     'varying vec3 vViewPos;',
     'varying vec3 vWorld;',
     'void main() {',
-        'vNormal = aNormal;',
+        'vec3 pos = aPos;',
+        'vec3 n = aNormal;',
+        'if (uCurvatureOn > 0.5) {',
+            'vec2 d = pos.xz - uCamPos.xz;',
+            'float r = max(1.0, uEarthRadius);',
+            'pos.y -= dot(d, d) / (2.0 * r);',
+            'n.x -= d.x / r;',
+            'n.z -= d.y / r;',
+            'n = normalize(n);',
+        '}',
+        'vNormal = n;',
         'vUV = aUV;',
-        'vY = aPos.y;',
-        'vWorld = aPos;',
-        'vec4 vp = uView * vec4(aPos, 1.0);',
+        'vY = pos.y;',
+        'vWorld = pos;',
+        'vec4 vp = uView * vec4(pos, 1.0);',
         'vViewPos = vp.xyz;',
         'gl_Position = uProj * vp;',
     '}'
@@ -888,6 +901,8 @@ function init(canvas) {
     var terrainUairColor = terrainProg ? gl.getUniformLocation(terrainProg, 'uAirColor') : null;
     var terrainUairDensity = terrainProg ? gl.getUniformLocation(terrainProg, 'uAirDensity') : null;
     var terrainUcampos = terrainProg ? gl.getUniformLocation(terrainProg, 'uCamPos') : null;
+    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 terrainUstarAmb = terrainProg ? gl.getUniformLocation(terrainProg, 'uStarAmb') : null;
     var terrainUtime = terrainProg ? gl.getUniformLocation(terrainProg, 'uTime') : null;
@@ -958,7 +973,9 @@ function init(canvas) {
             uSkyAmb: terrainUskyAmb, uAlbedoTint: terrainUalbedoTint,
             uHorizonColor: terrainUhorizon,
             uAirColor: terrainUairColor, uAirDensity: terrainUairDensity,
-            uCamPos: terrainUcampos, uEdgeFadeTiles: terrainUedgeFade,
+            uCamPos: terrainUcampos,
+            uEarthRadius: terrainUEarthRadius, uCurvatureOn: terrainUCurvatureOn,
+            uEdgeFadeTiles: terrainUedgeFade,
             uStarAmb: terrainUstarAmb,
             uTime: terrainUtime, uCloudBot: terrainUcloudbot,
             uCloudTop: terrainUcloudtop, uDensity: terrainUdensity,
@@ -2137,7 +2154,12 @@ var ATMO_MODEL_GRAY_TAU = (typeof ATMO_MODEL.grayTau === 'number')
     ? Math.max(0.1, Math.min(10.0, ATMO_MODEL.grayTau)) : 1.5;
 var ATMO_MODEL_GAIN = (typeof ATMO_MODEL.gain === 'number')
     ? Math.max(0.1, Math.min(5.0, ATMO_MODEL.gain)) : 2.0;
-var EARTH_RADIUS_UNITS = 6371.0 / KM_PER_TILE;
+var CURV_CFG = (window.CONFIG && window.CONFIG.curvature) || {};
+var CURVATURE_ON = CURV_CFG.enabled !== false;
+var CURV_EXAG = (typeof CURV_CFG.exaggeration === 'number')
+    ? Math.max(0.25, CURV_CFG.exaggeration) : 2.0;
+var EARTH_RADIUS_UNITS = (typeof CURV_CFG.earthRadiusKm === 'number'
+    ? Math.max(1000, CURV_CFG.earthRadiusKm) : 6371) / KM_PER_TILE / CURV_EXAG;
 var ATMO_MODEL_BLUE_COLOR = new Float32Array([0.22, 0.42, 0.95]);
 var ATMO_MODEL_GRAY_COLOR = new Float32Array([0.72, 0.76, 0.82]);
 // Integrated starlight + airglow. Physically this is about a millionth of
@@ -5490,6 +5512,8 @@ window.clouds3dRender = function(target) {
         gl.uniform3f(terr.uAirColor, _air[0], _air[1], _air[2]);
         gl.uniform1f(terr.uAirDensity, -Math.log(ATMO_HAZE_RESIDUAL) / Math.max(FOG_TILES, 0.001));
         gl.uniform3f(terr.uCamPos, camX, camY, camZ);
+        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.bindBuffer(gl.ARRAY_BUFFER, terr.vbo);