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/****************************************************************************
**
** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the QtQuick3D documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
** You may use this file in accordance with the terms and conditions
** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of this
** file.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\title Writing a scene format plug-in for Qt/3D
\example sceneformats/obj
Scene format plugins are used to load external 3D model file
formats like \bold 3DS, \bold obj, and so on. In this tutorial we will
do a walk-through of the \bold obj scene format plugin to
demonstrate what is required to add a new format to Qt/3D.
Models are loaded by QGLAbstractScene::loadScene(), which locates
a suitable plug-in for the format, and then asks the plug-in to
parse the data and create a QGLAbstractScene object that describes
the 3D objects in the scene.
We start by declaring an instance of QGLSceneFormatPlugin and
arranging for it to be registered with the Qt plug-in system:
\snippet sceneformats/obj/main.cpp 1
\snippet sceneformats/obj/main.cpp 4
The two functions we need to implement are
\l{QGLSceneFormatPlugin::keys()}{keys()} and
\l{QGLSceneFormatPlugin::create()}{create()}. The first of these
returns a lower-case list of the file extensions and MIME types
that are supported by the plug-in:
\snippet sceneformats/obj/main.cpp 2
The create function is called to create the QGLSceneFormatHandler
which is used to load the model data:
\snippet sceneformats/obj/main.cpp 3
The create function is passed the QIODevice for the data,
the URL of where the data was found, and the chosen format.
These parameters can be used by the plug-in to decide which
handler to return if multiple formats are supported by
the plug-in. In the case of obj, we always return the same
handler so we don't need to inspect the passed parameters.
QGLAbstractScene::loadScene() will set the parameters on
the QGLSceneFormatHandler object and then call
\l{QGLSceneFormatHandler::read()}{read()}:
\snippet sceneformats/obj/qglobjscenehandler.h 1
\dots
\snippet sceneformats/obj/qglobjscenehandler.h 2
The read function will typically construct a QGLBuilder
for the geometry in the scene and then parse all of the objects,
materials, textures, and so on. Ultimately, it needs to produce a
QGLAbstractScene object, populated with QGLSceneNode instances
for each of the objects in the model file. In our case, we create
an instance of \c QGLObjScene:
\snippet sceneformats/obj/qglobjscene.h 1
\dots
\snippet sceneformats/obj/qglobjscene.h 2
\dots
\snippet sceneformats/obj/qglobjscene.h 3
The most important function is the override for
QGLAbstractScene::objects(), which allows the rest of Qt/3D
to query the full list of objects in the model file.
The scene object can also override QGLAbstractScene::object()
if it has an efficient method to quickly look up an object by name.
The scene should also override QGLAbstractScene::mainNode()
to return the main mesh node in the scene. Usually this is
the first element in the list returned by QGLAbstractScene::objects()
but doesn't have to be.
Note: the plug-in does not need to use QGLBuilder and the
other Qt/3D classes to load the model if it doesn't want to.
It can instantiate subclasses of QGLSceneNode that override
the draw() method and draws the object using whatever technique
the plug-in chooses. It just needs to leave the OpenGL state
in the condition that it found it so that other parts of Qt/3D
will not be confused.
Once you have written a plug-in for your new format, you should
install it into \c{$QTDIR/plugins/sceneformats}. You can test it
by running the \c{modelviewer} program and trying to load models
in your new format. When debugging, it can be useful to set the
\c{QT_DEBUG_PLUGINS} environment variable to 1.
\l{qt3d-examples.html}{Return to the main Tutorials page}.
*/
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