source: trunk/src/gui/graphicsview/qgraphicstransform.cpp@ 858

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/*!
    \class QGraphicsTransform
    \brief The QGraphicsTransform class is an abstract base class for building
    advanced transformations on QGraphicsItems.
    \since 4.6
    \ingroup graphicsview-api

    As an alternative to QGraphicsItem::transform, QGraphicsTransform lets you
    create and control advanced transformations that can be configured
    independently using specialized properties.

    QGraphicsItem allows you to assign any number of QGraphicsTransform
    instances to one QGraphicsItem. Each QGraphicsTransform is applied in
    order, one at a time, to the QGraphicsItem it's assigned to.

    QGraphicsTransform is particularly useful for animations. Whereas
    QGraphicsItem::setTransform() lets you assign any transform directly to an
    item, there is no direct way to interpolate between two different
    transformations (e.g., when transitioning between two states, each for
    which the item has a different arbitrary transform assigned). Using
    QGraphicsTransform you can interpolate the property values of each
    independent transformation. The resulting operation is then combined into a
    single transform which is applied to QGraphicsItem.

    Transformations are computed in true 3D space using QMatrix4x4.
    When the transformation is applied to a QGraphicsItem, it will be
    projected back to a 2D QTransform.  When multiple QGraphicsTransform
    objects are applied to a QGraphicsItem, all of the transformations
    are computed in true 3D space, with the projection back to 2D
    only occurring after the last QGraphicsTransform is applied.
    The exception to this is QGraphicsRotation, which projects back to
    2D after each rotation to preserve the perspective effect around
    the X and Y axes.

    If you want to create your own configurable transformation, you can create
    a subclass of QGraphicsTransform (or any or the existing subclasses), and
    reimplement the pure virtual applyTo() function, which takes a pointer to a
    QMatrix4x4. Each operation you would like to apply should be exposed as
    properties (e.g., customTransform->setVerticalShear(2.5)). Inside you
    reimplementation of applyTo(), you can modify the provided transform
    respectively.

    QGraphicsTransform can be used together with QGraphicsItem::setTransform(),
    QGraphicsItem::setRotation(), and QGraphicsItem::setScale().

    \sa QGraphicsItem::transform(), QGraphicsScale, QGraphicsRotation
*/

#include "qgraphicstransform.h"
#include "qgraphicsitem_p.h"
#include "qgraphicstransform_p.h"
#include <QDebug>
#include <QtCore/qmath.h>

#ifndef QT_NO_GRAPHICSVIEW
QT_BEGIN_NAMESPACE
void QGraphicsTransformPrivate::setItem(QGraphicsItem *i)
{
    if (item == i)
        return;

    if (item) {
        Q_Q(QGraphicsTransform);
        QGraphicsItemPrivate *d_ptr = item->d_ptr.data();

        item->prepareGeometryChange();
        Q_ASSERT(d_ptr->transformData);
        d_ptr->transformData->graphicsTransforms.removeAll(q);
        d_ptr->dirtySceneTransform = 1;
        item = 0;
    }

    item = i;
}

void QGraphicsTransformPrivate::updateItem(QGraphicsItem *item)
{
    item->prepareGeometryChange();
    item->d_ptr->dirtySceneTransform = 1;
}

/*!
    Constructs a new QGraphicsTransform with the given \a parent.
*/
QGraphicsTransform::QGraphicsTransform(QObject *parent)
    : QObject(*new QGraphicsTransformPrivate, parent)
{
}

/*!
    Destroys the graphics transform.
*/
QGraphicsTransform::~QGraphicsTransform()
{
    Q_D(QGraphicsTransform);
    d->setItem(0);
}

/*!
    \internal
*/
QGraphicsTransform::QGraphicsTransform(QGraphicsTransformPrivate &p, QObject *parent)
    : QObject(p, parent)
{
}

/*!
    \fn void QGraphicsTransform::applyTo(QMatrix4x4 *matrix) const

    This pure virtual method has to be reimplemented in derived classes.

    It applies this transformation to \a matrix.

    \sa QGraphicsItem::transform(), QMatrix4x4::toTransform()
*/

/*!
    Notifies that this transform operation has changed its parameters in such a
    way that applyTo() will return a different result than before.

    When implementing you own custom graphics transform, you must call this