Increase precision when normalizing vectors

QVector3D::normalize() and other similar functions were losing
precision when qreal was float, causing vectors with small lengths
to normalize to (0, 0, 0).  Do the length calculations with
double precision to avoid this problem.

Reviewed-by: Sarah Smith

1 files changed, 8 insertions, 2 deletions

diff --git a/src/gui/math3d/qvector3d.cpp b/src/gui/math3d/qvector3d.cpp
index 7d4ddf7..9552e3a 100644
--- a/src/gui/math3d/qvector3d.cpp
+++ b/src/gui/math3d/qvector3d.cpp
@@ -205,7 +205,10 @@ QVector3D::QVector3D(const QVector4D& vector)
 */
 QVector3D QVector3D::normalized() const
 {
-    qreal len = lengthSquared();
+    // Need some extra precision if the length is very small.
+    double len = double(xp) * double(xp) +
+                 double(yp) * double(yp) +
+                 double(zp) * double(zp);
     if (qFuzzyIsNull(len - 1.0f))
         return *this;
     else if (!qFuzzyIsNull(len))
@@ -222,7 +225,10 @@ QVector3D QVector3D::normalized() const
 */
 void QVector3D::normalize()
 {
-    qreal len = lengthSquared();
+    // Need some extra precision if the length is very small.
+    double len = double(xp) * double(xp) +
+                 double(yp) * double(yp) +
+                 double(zp) * double(zp);
     if (qFuzzyIsNull(len - 1.0f) || qFuzzyIsNull(len))
         return;