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/****************************************************************************
**
** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the Qt3D module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** GNU Lesser General Public License Usage
** This file may be used under the terms of the GNU Lesser General Public
** License version 2.1 as published by the Free Software Foundation and
** appearing in the file LICENSE.LGPL included in the packaging of this
** file. Please review the following information to ensure the GNU Lesser
** General Public License version 2.1 requirements will be met:
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU General
** Public License version 3.0 as published by the Free Software Foundation
** and appearing in the file LICENSE.GPL included in the packaging of this
** file. Please review the following information to ensure the GNU General
** Public License version 3.0 requirements will be met:
** http://www.gnu.org/copyleft/gpl.html.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms and
** conditions contained in a signed written agreement between you and Nokia.
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "qgraphicsbillboardtransform.h"
QT_BEGIN_NAMESPACE
/*!
\class QGraphicsBillboardTransform
\brief The QGraphicsBillboardTransform class implements a transformation that causes objects to face the camera.
\since 4.8
\ingroup qt3d
\ingroup qt3d::graphicsview
Sometimes it can be useful to make an object face towards the camera
no matter what orientation the scene is in. The common name for
this technique is "billboarding".
When applied as a transformation, this class will replace the top-left
3x3 part of the transformation matrix with the identity. This has the
effect of removing the rotation and scale components from the current
world co-ordinate orientation.
*/
/*!
\qmlclass BillboardTransform QGraphicsBillboardTransform
\brief The BillboardTransform item implements a transformation that causes objects to face the camera.
\since 4.8
\ingroup qt3d::qml3d
Sometimes it can be useful to make an object face towards the camera
no matter what orientation the scene is in. The common name for
this technique is "billboarding".
When applied as a transformation, this class will replace the top-left
3x3 part of the transformation matrix with the identity. This has the
effect of removing the rotation and scale components from the current
world co-ordinate orientation. In QML, this can be used as follows
to orient a pane to point towards the viewer:
\code
Item3D {
mesh: Mesh { source: "pane.obj" }
position: Qt.vector3d(2, 0, -20)
transform: BillboardTransform {}
effect: Effect { texture: "picture.jpg" }
}
\endcode
Because the billboard transformation will strip any further
alterations to the matrix, it will usually be the last element
in the \c transform list (transformations are applied to the matrix in
reverse order of their appearance in \c transform):
\code
Item3D {
mesh: Mesh { source: "pane.obj" }
position: Qt.vector3d(2, 0, -20)
transform: [
Scale3D { scale: 0.5 },
Rotation3D { angle: 30 },
BillboardTransform {}
]
effect: Effect { texture: "picture.jpg" }
}
\endcode
The \c scale property is applied to the matrix after \c transform has
performed the billboard transformation, so the above can also be written
as follows:
\code
Item3D {
mesh: Mesh { source: "pane.obj" }
position: Qt.vector3d(2, 0, -20)
scale: 0.5
transform: [
Rotation3D { angle: 30 },
BillboardTransform {}
]
effect: Effect { texture: "picture.jpg" }
}
\endcode
By default the billboard transform will cause the object to
face directly at the camera no matter how the world co-ordinate
system is rotated. Sometimes the billboard needs to stay at right
angles to the "ground plane" even if the user's viewpoint is
elevated. This behavior can be enabled using the preserveUpVector
property:
\code
Pane {
position: Qt.vector3d(2, 0, -20)
transform: BillboardTransform { preserveUpVector: true }
effect: Effect { texture: "picture.jpg" }
}
\endcode
*/
class QGraphicsBillboardTransformPrivate
{
public:
QGraphicsBillboardTransformPrivate() : preserveUpVector(false) {}
bool preserveUpVector;
};
/*!
Construct a billboard transform and attach it to \a parent.
*/
QGraphicsBillboardTransform::QGraphicsBillboardTransform(QObject *parent)
: QGraphicsTransform3D(parent), d_ptr(new QGraphicsBillboardTransformPrivate)
{
}
/*!
Destroy this billboard transform.
*/
QGraphicsBillboardTransform::~QGraphicsBillboardTransform()
{
}
/*!
\property QGraphicsBillboardTransform::preserveUpVector
\brief true to preserve the up orientation.
The default value for this property is false, which indicates that
the object being transformed should always face directly to the camera
This is also known as a "spherical billboard".
If the value for this property is true, then the object will have
its up orientation preserved. This is also known as a "cylindrical
billboard".
*/
/*!
\qmlproperty bool BillboardTransform::preserveUpVector
This property specifies whether the billboard transform should
preserve the "up vector" so that objects stay at right angles
to the ground plane in the scene.
The default value for this property is false, which indicates that
the object being transformed should always face directly to the camera
This is also known as a "spherical billboard".
If the value for this property is true, then the object will have
its up orientation preserved. This is also known as a "cylindrical
billboard".
*/
bool QGraphicsBillboardTransform::preserveUpVector() const
{
Q_D(const QGraphicsBillboardTransform);
return d->preserveUpVector;
}
void QGraphicsBillboardTransform::setPreserveUpVector(bool value)
{
Q_D(QGraphicsBillboardTransform);
if (d->preserveUpVector != value) {
d->preserveUpVector = value;
emit transformChanged();
emit preserveUpVectorChanged();
}
}
/*!
\internal
*/
void QGraphicsBillboardTransform::applyTo(QMatrix4x4 *matrix) const
{
Q_D(const QGraphicsBillboardTransform);
if (!d->preserveUpVector) {
// Replace the top-left 3x3 of the matrix with the identity.
// The technique is "Cheating Spherical Billboards", described here:
// http://www.lighthouse3d.com/opengl/billboarding/index.php?billCheat
(*matrix)(0, 0) = 1.0f;
(*matrix)(0, 1) = 0.0f;
(*matrix)(0, 2) = 0.0f;
(*matrix)(1, 0) = 0.0f;
(*matrix)(1, 1) = 1.0f;
(*matrix)(1, 2) = 0.0f;
(*matrix)(2, 0) = 0.0f;
(*matrix)(2, 1) = 0.0f;
(*matrix)(2, 2) = 1.0f;
} else {
// Replace some of the top-left 3x3 of the matrix with the identity,
// but leave the up vector component in the second column as-is.
// The technique is "Cheating Cylindrical Billboards", described here:
// http://www.lighthouse3d.com/opengl/billboarding/index.php?billCheat1
(*matrix)(0, 0) = 1.0f;
(*matrix)(0, 2) = 0.0f;
(*matrix)(1, 0) = 0.0f;
(*matrix)(1, 2) = 0.0f;
(*matrix)(2, 0) = 0.0f;
(*matrix)(2, 2) = 1.0f;
}
matrix->optimize();
}
/*!
\internal
*/
QGraphicsTransform3D *QGraphicsBillboardTransform::clone(QObject *parent) const
{
Q_D(const QGraphicsBillboardTransform);
QGraphicsBillboardTransform *copy = new QGraphicsBillboardTransform(parent);
copy->setPreserveUpVector(d->preserveUpVector);
return copy;
}
/*!
\fn void QGraphicsBillboardTransform::preserveUpVectorChanged()
Signal that is emitted when preserveUpVector() changes.
*/
QT_END_NAMESPACE
|
