diff -r c1080cb5bd6d -r fbdeb3e04543 src/scene.cc
--- a/src/scene.cc	Tue Dec 18 12:36:01 2007 +0100
+++ b/src/scene.cc	Sat Dec 29 13:53:33 2007 +0100
@@ -95,10 +95,10 @@
 bool Sphere::intersect(const Ray &ray, Float &dist) const
 {
 	Vector3 V = ray.o - center;
-	register Float d = -dot(V, ray.dir);
+	register Float d = dot(V, ray.dir);
 	register Float Det = d * d - (dot(V,V) - sqr_radius);
 	if (Det > 0) {
-		d -= sqrtf(Det);
+		d = -d - sqrtf(Det);
 		if (d > 0 && d < dist)
 		{
 			dist = d;