QMatrix4x4::mapVector() to transform by top-left 3x3

It is useful to be able to map direction vectors by the top-left
3x3 component of a 4x4 matrix, ignoring the translation and
projection components.

Reviewed-by: Sarah Smith

2 files changed, 33 insertions, 1 deletions

diff --git a/src/gui/math3d/qmatrix4x4.cpp b/src/gui/math3d/qmatrix4x4.cpp
index 123c0f041c..ed1b13d4dd 100644
--- a/src/gui/math3d/qmatrix4x4.cpp
+++ b/src/gui/math3d/qmatrix4x4.cpp
@@ -1502,7 +1502,17 @@ QTransform QMatrix4x4::toTransform(qreal distanceToPlane) const
 
     Maps \a point by multiplying this matrix by \a point.
 
-    \sa mapRect()
+    \sa mapRect(), mapVector()
+*/
+
+/*!
+    \fn QVector3D QMatrix4x4::mapVector(const QVector3D& vector) const
+
+    Maps \a vector by multiplying the top 3x3 portion of this matrix
+    by \a vector.  The translation and projection components of
+    this matrix are ignored.
+
+    \sa map()
 */
 
 #endif
diff --git a/src/gui/math3d/qmatrix4x4.h b/src/gui/math3d/qmatrix4x4.h
index 7631ae72cf..cfa3f2a7a0 100644
--- a/src/gui/math3d/qmatrix4x4.h
+++ b/src/gui/math3d/qmatrix4x4.h
@@ -165,6 +165,7 @@ public:
     QPointF map(const QPointF& point) const;
 #ifndef QT_NO_VECTOR3D
     QVector3D map(const QVector3D& point) const;
+    QVector3D mapVector(const QVector3D& vector) const;
 #endif
 #ifndef QT_NO_VECTOR4D
     QVector4D map(const QVector4D& point) const;
@@ -940,6 +941,27 @@ inline QVector3D QMatrix4x4::map(const QVector3D& point) const
     return *this * point;
 }
 
+inline QVector3D QMatrix4x4::mapVector(const QVector3D& vector) const
+{
+    if (flagBits == Identity || flagBits == Translation) {
+        return vector;
+    } else if (flagBits == Scale || flagBits == (Translation | Scale)) {
+        return QVector3D(vector.x() * m[0][0],
+                         vector.y() * m[1][1],
+                         vector.z() * m[2][2]);
+    } else {
+        return QVector3D(vector.x() * m[0][0] +
+                         vector.y() * m[1][0] +
+                         vector.z() * m[2][0],
+                         vector.x() * m[0][1] +
+                         vector.y() * m[1][1] +
+                         vector.z() * m[2][1],
+                         vector.x() * m[0][2] +
+                         vector.y() * m[1][2] +
+                         vector.z() * m[2][2]);
+    }
+}
+
 #endif
 
 #ifndef QT_NO_VECTOR4D