diff options
Diffstat (limited to 'src/gui/math3d/qmatrix4x4.cpp')
| -rw-r--r-- | src/gui/math3d/qmatrix4x4.cpp | 53 |
1 files changed, 47 insertions, 6 deletions
diff --git a/src/gui/math3d/qmatrix4x4.cpp b/src/gui/math3d/qmatrix4x4.cpp index 8fc439b..ed0802b 100644 --- a/src/gui/math3d/qmatrix4x4.cpp +++ b/src/gui/math3d/qmatrix4x4.cpp @@ -1438,18 +1438,59 @@ QMatrix QMatrix4x4::toAffine() const qreal(m[3][0]), qreal(m[3][1])); } +static const qreal inv_dist_to_plane = 1. / 1024.; + /*! Returns the conventional Qt 2D transformation matrix that - corresponds to this matrix. It is assumed that this matrix - only contains 2D transformation elements. + corresponds to this matrix. + + If \a distanceToPlane is non-zero, it indicates a projection + factor to use to adjust for the z co-ordinate. The default + value of 1024 corresponds to the projection factor used + by QTransform::rotate() for the x and y axes. + + If \a distToPlane is zero, then the returned QTransform + is formed by simply dropping the third row and third column + of the QMatrix4x4. This is suitable for implementing + orthographic projections where the z co-ordinate should + be dropped rather than projected. \sa toAffine() */ -QTransform QMatrix4x4::toTransform() const +QTransform QMatrix4x4::toTransform(qreal distanceToPlane) const { - return QTransform(qreal(m[0][0]), qreal(m[0][1]), qreal(m[0][3]), - qreal(m[1][0]), qreal(m[1][1]), qreal(m[1][3]), - qreal(m[3][0]), qreal(m[3][1]), qreal(m[3][3])); + if (distanceToPlane == 1024.0f) { + // Optimize the common case with constants. + return QTransform(qreal(m[0][0]), qreal(m[0][1]), + qreal(m[0][3]) - qreal(m[0][2]) * + inv_dist_to_plane, + qreal(m[1][0]), qreal(m[1][1]), + qreal(m[1][3]) - qreal(m[1][2]) * + inv_dist_to_plane, + qreal(m[3][0]), qreal(m[3][1]), + qreal(m[3][3]) - qreal(m[3][2]) * + inv_dist_to_plane); + } else if (distanceToPlane != 0.0f) { + // The following projection matrix is pre-multiplied with "matrix": + // | 1 0 0 0 | + // | 0 1 0 0 | + // | 0 0 1 0 | + // | 0 0 d 1 | + // where d = -1 / distanceToPlane. After projection, row 3 and + // column 3 are dropped to form the final QTransform. + qreal d = 1.0f / distanceToPlane; + return QTransform(qreal(m[0][0]), qreal(m[0][1]), + qreal(m[0][3]) - qreal(m[0][2]) * d, + qreal(m[1][0]), qreal(m[1][1]), + qreal(m[1][3]) - qreal(m[1][2]) * d, + qreal(m[3][0]), qreal(m[3][1]), + qreal(m[3][3]) - qreal(m[3][2]) * d); + } else { + // Orthographic projection: drop row 3 and column 3. + return QTransform(qreal(m[0][0]), qreal(m[0][1]), qreal(m[0][3]), + qreal(m[1][0]), qreal(m[1][1]), qreal(m[1][3]), + qreal(m[3][0]), qreal(m[3][1]), qreal(m[3][3])); + } } /*! |