Fix shader: pass uFlightDir as uniform instead of window access

The shader had the JS code 'window.__flightDir.dx' baked into the
GLSL string, which GLSL can't parse. Added a uFlightDir uniform
(vec2) and pass the dx/dz from JS via gl.uniform2f. Shader reads
uFlightDir.x and uFlightDir.y.

vendor/clouds3d.js

@@ -56,6 +56,7 @@ var FRAG_SRC = [
     'uniform sampler2D uGround;',
     'uniform vec2 uGroundCenter;',  // current mosaic centre (world units)
     'uniform vec2 uGroundSize;',    // mosaic side extents in X and Z (world units)
+    'uniform vec2 uFlightDir;',     // camera motion direction (dx, dz)
     'uniform vec3 uSky;',
     'uniform vec3 uCloud;',
     'uniform vec3 uCloudShadow;',
@@ -143,7 +144,7 @@ var FRAG_SRC = [
         // Default: drift along +Z (north). For east: drift along +X. For south: -Z, etc.
         'float fdx = (window.__flightDir ? window.__flightDir.dx : 0.0);',
         'float fdz = (window.__flightDir ? window.__flightDir.dz : 1.0);',
-        'vec3 ro = vec3(drift * fdx, camY, drift * fdz);',
+        'vec3 ro = vec3(drift * uFlightDir.x, camY, drift * uFlightDir.y);',
         // Ray direction: tilt more downward so the visible ground fits
         // within the mosaic. At uv.y = 0 the ray goes ~26° below
         // horizontal, putting the visible ground at tGround < 5
@@ -251,6 +252,7 @@ function init(canvas) {
     var uGround = gl.getUniformLocation(prog, 'uGround');
     var uGroundCenter = gl.getUniformLocation(prog, 'uGroundCenter');
     var uGroundSize = gl.getUniformLocation(prog, 'uGroundSize');
+    var uFlightDir = gl.getUniformLocation(prog, 'uFlightDir');
     var uSky = gl.getUniformLocation(prog, 'uSky');
     var uCloud = gl.getUniformLocation(prog, 'uCloud');
     var uCloudShadow = gl.getUniformLocation(prog, 'uCloudShadow');
@@ -265,6 +267,7 @@ function init(canvas) {
         gl: gl, prog: prog, buf: buf, aPos: aPos,
         uRes: uRes, uTime: uTime, uGround: uGround,
         uGroundCenter: uGroundCenter, uGroundSize: uGroundSize,
+        uFlightDir: uFlightDir,
         uSky: uSky, uCloud: uCloud,
         uCloudShadow: uCloudShadow, uLight: uLight, uBg: uBg,
         uSpeed: uSpeed, uDensity: uDensity, uDayProgress: uDayProgress,
@@ -542,6 +545,9 @@ window.clouds3dRender = function(target) {
     };
     gl.uniform2f(s.uGroundCenter, centerWorld.x, centerWorld.y);
     gl.uniform2f(s.uGroundSize, GROUND_CORRIDOR_PERP, GROUND_CORRIDOR_LONG);
+    var flightDir = (window.__flightDir && (window.__flightDir.dx !== undefined))
+        ? window.__flightDir : { dx: 0, dz: 1 };
+    gl.uniform2f(s.uFlightDir, flightDir.dx, flightDir.dz);
 
     var drift = now * speed * 0.12;
     if (performance.now() - groundLastCheck > 1500) {