Introduce QMatrix4x4::isAffine()

- a convenience method thats checks if the matrix
has no projective coefficients.

Change-Id: Ieea8ac2e4237b471a683ad5010672b1e89a0c953
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

src/gui/math3d/qmatrix4x4.cpp

@@ -289,6 +289,18 @@ QMatrix4x4::QMatrix4x4(const QTransform& transform)
     \sa row(), setColumn()
 */
 
+/*!
+    \fn bool QMatrix4x4::isAffine() const
+    \since 5.5
+
+    Returns \c true if this matrix is affine matrix; false otherwise.
+
+    An affine matrix is a 4x4 matrix with row 3 equal to (0, 0, 0, 1),
+    e.g. no projective coefficients.
+
+    \sa isIdentity()
+*/
+
 /*!
     \fn bool QMatrix4x4::isIdentity() const
 

src/gui/math3d/qmatrix4x4.h

@@ -77,6 +77,8 @@ public:
     inline void setRow(int index, const QVector4D& value);
 #endif
 
+    inline bool isAffine() const;
+
     inline bool isIdentity() const;
     inline void setToIdentity();
 
@@ -302,6 +304,11 @@ inline void QMatrix4x4::setRow(int index, const QVector4D& value)
 
 Q_GUI_EXPORT QMatrix4x4 operator/(const QMatrix4x4& matrix, float divisor);
 
+inline bool QMatrix4x4::isAffine() const
+{
+    return m[0][3] == 0.0f && m[1][3] == 0.0f && m[2][3] == 0.0f && m[3][3] == 1.0f;
+}
+
 inline bool QMatrix4x4::isIdentity() const
 {
     if (flagBits == Identity)