Fix bug #2006:

Floating point imprecision made MT_Quaternion::angle return NaN, since acos(x) is NaN for |x| > 1.

Because of the way NaN's propagate through float math, the view pos would be set to [NaN, NaN, NaN] resulting in a grey screen.

2 files changed, 16 insertions, 2 deletions

diff --git a/intern/moto/include/MT_Quaternion.inl b/intern/moto/include/MT_Quaternion.inl
index 8b4fbc93c41..ecfd6699f67 100644
--- a/intern/moto/include/MT_Quaternion.inl
+++ b/intern/moto/include/MT_Quaternion.inl
@@ -64,13 +64,19 @@ GEN_INLINE MT_Scalar MT_Quaternion::angle(const MT_Quaternion& q) const
 {
 	MT_Scalar s = sqrt(length2() * q.length2());
 	assert(s != MT_Scalar(0.0));
-	return acos(dot(q) / s);
+	
+	s = dot(q) / s;
+	
+	s = MT_clamp(s, -1.0, 1.0);
+	
+	return acos(s);
 }
 
 GEN_INLINE MT_Quaternion MT_Quaternion::slerp(const MT_Quaternion& q, const MT_Scalar& t) const
 {
 	MT_Scalar theta = angle(q);
-	if (theta != MT_Scalar(0.0))
+	
+	if (!MT_fuzzyZero(theta))
 	{
 		MT_Scalar d = MT_Scalar(1.0) / sin(theta);
 		MT_Scalar s0 = sin((MT_Scalar(1.0) - t) * theta);
diff --git a/intern/moto/include/MT_Scalar.h b/intern/moto/include/MT_Scalar.h
index 0a72a52c20e..6ee0948f244 100755
--- a/intern/moto/include/MT_Scalar.h
+++ b/intern/moto/include/MT_Scalar.h
@@ -83,5 +83,13 @@ inline MT_Scalar MT_random() {
     return MT_Scalar(MT_rand()) / MT_Scalar(MT_RAND_MAX);
 }
 
+inline MT_Scalar MT_clamp(const MT_Scalar x, const MT_Scalar min, const MT_Scalar max)
+{
+	if (x < min)
+		return min;
+	else if (x > max)
+		return max;
+	return x;
+}
 #endif