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QGraphicsRotation Class

The QGraphicsRotation class provides a rotation transformation around a given axis. More...

Header: #include <QGraphicsRotation>
qmake: QT += widgets
Since: Qt 4.6
Inherits: QGraphicsTransform

This class was introduced in Qt 4.6.

Properties

Public Functions

QGraphicsRotation(QObject *parent = nullptr)
virtual ~QGraphicsRotation()
qreal angle() const
QVector3D axis() const
QVector3D origin() const
void setAngle(qreal)
void setAxis(const QVector3D &axis)
void setAxis(Qt::Axis axis)
void setOrigin(const QVector3D &point)

Reimplemented Public Functions

virtual void applyTo(QMatrix4x4 *matrix) const override

Signals

void angleChanged()
void axisChanged()
void originChanged()

Detailed Description

You can provide the desired axis by assigning a QVector3D to the axis property or by passing a member if Qt::Axis to the setAxis convenience function. By default the axis is (0, 0, 1) i.e., rotation around the Z axis.

The angle property, which is provided by QGraphicsRotation, now describes the number of degrees to rotate around this axis.

QGraphicsRotation provides certain parameters to help control how the rotation should be applied.

The origin is the point that the item is rotated around (i.e., it stays fixed relative to the parent as the rest of the item is rotated). By default the origin is QPointF(0, 0).

The angle property provides the number of degrees to rotate the item clockwise around the origin. This value also be negative, indicating a counter-clockwise rotation. For animation purposes it may also be useful to provide rotation angles exceeding (-360, 360) degrees, for instance to animate how an item rotates several times.

Note: the final rotation is the combined effect of a rotation in 3D space followed by a projection back to 2D. If several rotations are performed in succession, they will not behave as expected unless they were all around the Z axis.

See also QGraphicsTransform, QGraphicsItem::setRotation(), and QTransform::rotate().

Property Documentation

angle : qreal

This property holds the angle for clockwise rotation, in degrees.

The angle can be any real number; the default value is 0.0. A value of 180 will rotate 180 degrees, clockwise. If you provide a negative number, the item will be rotated counter-clockwise. Normally the rotation angle will be in the range (-360, 360), but you can also provide numbers outside of this range (e.g., a angle of 370 degrees gives the same result as 10 degrees). Setting the angle to NaN results in no rotation.

Access functions:

qreal angle() const
void setAngle(qreal)

Notifier signal:

void angleChanged()

See also origin.

axis : QVector3D

This property holds a rotation axis, specified by a vector in 3D space.

This can be any axis in 3D space. By default the axis is (0, 0, 1), which is aligned with the Z axis. If you provide another axis, QGraphicsRotation will provide a transformation that rotates around this axis. For example, if you would like to rotate an item around its X axis, you could pass (1, 0, 0) as the axis.

Access functions:

QVector3D axis() const
void setAxis(const QVector3D &axis)
void setAxis(Qt::Axis axis)

Notifier signal:

void axisChanged()

See also QTransform and QGraphicsRotation::angle.

origin : QVector3D

This property holds the origin of the rotation in 3D space.

All rotations will be done relative to this point (i.e., this point will stay fixed, relative to the parent, when the item is rotated).

Access functions:

QVector3D origin() const
void setOrigin(const QVector3D &point)

Notifier signal:

void originChanged()

See also angle.

Member Function Documentation

QGraphicsRotation::QGraphicsRotation(QObject *parent = nullptr)

Constructs a new QGraphicsRotation with the given parent.

[signal] void QGraphicsRotation::angleChanged()

This signal is emitted whenever the angle has changed.

Note: Notifier signal for property angle.

See also QGraphicsRotation::angle.

[signal] void QGraphicsRotation::axisChanged()

This signal is emitted whenever the axis of the object changes.

Note: Notifier signal for property axis.

See also QGraphicsRotation::axis.

[signal] void QGraphicsRotation::originChanged()

This signal is emitted whenever the origin has changed.

Note: Notifier signal for property origin.

See also QGraphicsRotation::origin.

[virtual] QGraphicsRotation::~QGraphicsRotation()

Destroys the graphics rotation.

[override virtual] void QGraphicsRotation::applyTo(QMatrix4x4 *matrix) const

Reimplements: QGraphicsTransform::applyTo(QMatrix4x4 *matrix) const.

void QGraphicsRotation::setAxis(Qt::Axis axis)

Convenience function to set the axis to axis.

Note: the Qt::YAxis rotation for QTransform is inverted from the correct mathematical rotation in 3D space. The QGraphicsRotation class implements a correct mathematical rotation. The following two sequences of code will perform the same transformation:

QTransform t;
t.rotate(45, Qt::YAxis);

QGraphicsRotation r;
r.setAxis(Qt::YAxis);
r.setAngle(-45);

Note: Setter function for property axis.

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