Merge branch 'feature/globebrowsing' into feature/globe-atmosphere

modules/globebrowsing/shaders/ellipsoid.hglsl

@@ -30,6 +30,12 @@ struct PositionNormalPair {
 	vec3 normal;
 };
 
+struct Intersection {
+    bool  intersects;
+    float nearParameter;// Along ray
+    float farParameter;	// Along ray
+};
+
 vec3 geodeticSurfaceNormal(float latitude, float longitude)
 {
 	float cosLat = cos(latitude);
@@ -68,4 +74,33 @@ vec3 latLonToCartesian(float latitude, float longitude, float radius) {
 		sin(latitude));
 }
 
+//
+// Assumes ellipsoid is at (0, 0, 0)
+//
+Intersection rayIntersectEllipsoid(
+	vec3 rayOrigin,
+	vec3 rayOriginSquared,
+	vec3 rayDirection,
+	vec3 oneOverEllipsoidRadiiSquared)
+{
+    float a = dot(rayDirection * rayDirection, oneOverEllipsoidRadiiSquared);
+    float b = 2.0 * dot(rayOrigin * rayDirection, oneOverEllipsoidRadiiSquared);
+    float c = dot(rayOriginSquared, oneOverEllipsoidRadiiSquared) - 1.0;
+    float discriminant = b * b - 4.0 * a * c;
+
+    if (discriminant < 0.0) {
+        return Intersection(false, 0.0, 0.0);
+    }
+    else if (discriminant == 0.0) {
+        float time = -0.5 * b / a;
+        return Intersection(true, time, time);
+    }
+
+    float t = -0.5 * (b + (b > 0.0 ? 1.0 : -1.0) * sqrt(discriminant));
+    float root1 = t / a;
+    float root2 = c / t;
+
+    return Intersection(true, min(root1, root2), max(root1, root2));
+}
+
 #endif // ELLIPSOID_HGLSL