add fix for circular orbit rendering

src/renderer.cpp

@@ -367,7 +367,14 @@ struct OrbitalBasis {
 
 static OrbitalBasis calculate_orbital_basis(Vec3 r_vec, Vec3 velocity, Vec3 e_vec) {
     OrbitalBasis basis;
-    basis.periapsis_dir = vec3_normalize(e_vec);
+    Vec3 e_dir = vec3_normalize(e_vec);
+
+    // For circular orbits, use position direction as periapsis direction
+    if (vec3_magnitude(e_dir) < 0.001) {
+        basis.periapsis_dir = vec3_normalize(r_vec);
+    } else {
+        basis.periapsis_dir = e_dir;
+    }
 
     Vec3 h_vec = vec3_cross(r_vec, velocity);
     basis.normal = vec3_normalize(h_vec);