[Interest] Qt3D : QSceneLoader - determining scene level geometry bounding box
Nicholas Yue
yue.nicholas at gmail.com
Thu Aug 4 00:44:24 CEST 2022
I have the following code
```
void SceneWalker::walkEntity(Qt3DCore::QEntity *e, int depth)
{
Qt3DCore::QNodeVector nodes = e->childNodes();
for (int i = 0; i < nodes.count(); ++i) {
Qt3DCore::QNode *node = nodes[i];
Qt3DCore::QEntity *entity = qobject_cast<Qt3DCore::QEntity *>(node);
if (entity) {
QString indent;
indent.fill(' ', depth * 2);
qDebug().noquote() << indent << "Entity:" << entity <<
"Components:" << entity->components();
{
// Question about BoundingVolume
qDebug() << "BoundingVolume: " << entity->objectName();
const QList<Qt3DRender::QGeometryRenderer *>
myQGeometryRenderer =
entity->componentsOfType<Qt3DRender::QGeometryRenderer>();
if (!myQGeometryRenderer.isEmpty())
{
Qt3DRender::QGeometryRenderer *gr = myQGeometryRenderer[0];
QVector3D minPoint = gr->implicitMinPoint();
QVector3D maxPoint = gr->implicitMaxPoint();
qDebug() << "minPoint: " << minPoint;
qDebug() << "maxPoint: " << maxPoint;
}
}
walkEntity(entity, depth + 1);
}
}
}
```
But I got the (0,0,0) for both the min/max point
```
Status changed: Qt3DRender::QSceneLoader::Loading
Status changed: Qt3DRender::QSceneLoader::Ready
Entity: Qt3DCore::QEntity(0x7f65dc004660, name = untitled.obj) Components:
QList(Qt3DCore::QTransform(0x7f65dc04c590))
Entity: Qt3DCore::QEntity(0x7f65dc019220, name = Suzanne) Components:
QList(Qt3DExtras::QPhongMaterial(0x7f65dc01bf30, name = DefaultMaterial),
Qt3DRender::QGeometryRenderer(0x7f65dc00c4d0),
Qt3DCore::QTransform(0x7f65dc045800))
BoundingVolume: "Suzanne"
minPoint: QVector3D(0, 0, 0)
maxPoint: QVector3D(0, 0, 0)
BoundingVolume: "untitled.obj"
```
I am using Qt 6.2.2 on Ubuntu
Cheers
On Wed, 3 Aug 2022 at 01:25, Mike Krus <mike.krus at kdab.com> wrote:
> Hi
>
> once the scene is loaded (ie, the status is Ready, keeping in mind loading
> is asynchronous), you can use
> QSceneLoader::entity() to get a loaded entity by name, and then
> QEntity::componentsOfType() to get the component.
> Loaded entities are children of the entity that the QSceneLoader component
> was assigned to, and components and
> entities are all QObjects so you can use the normal tree traversal
> techniques that work with any QObject to find
> objects by type or name.
>
>
> Mike
>
> > On 3 Aug 2022, at 00:14, Nicholas Yue <yue.nicholas at gmail.com> wrote:
> >
> > Thank you Mike.
> >
> > Follow up question:
> >
> > Given a
> >
> > ```
> > Qt3DRender::QSceneLoader *sceneLoader;
> > ```
> >
> > How do we get at this QGeometryRenderer object to be able to call the
> impliciteMinPoint (), impliciteMaxPoint () properties ?
> >
> > Cheers
> >
> > On Tue, 2 Aug 2022 at 05:56, Mike Krus <mike.krus at kdab.com> wrote:
> > Hi
> >
> > if you are using Qt6, then yes.
> >
> > For a specific object, QGeometryRenderer derives from QBoundingVolume
> which has impliciteMinPoint and impliciteMaxPoint properties.
> >
> > If you’re interested in the bounding volume of a portion of the scene
> graph, all a QBoundingVolume component at the root and the
> > same properties will be updated.
> >
> > In Qt5, the QGeometry node associated with each render has similar
> min/max properties (note that they only valid if the mesh uses all the
> geometry).
> >
> > Hope this helps,
> >
> > Mike
> >
> >
> > > On 1 Aug 2022, at 16:05, Nicholas Yue <yue.nicholas at gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > I am diving into the geometry scene via QSceneLoader.
> > >
> > > Using the following code as a starting point, I wish to place the
> camera such that it automatically accommodates scenes of different sizes.
> > >
> > > One way I am thinking of doing is to base on the scene geometry
> bounding box.
> > >
> > > Is there a method or API which I can call to query the entire scene
> geometry bounding box ? Or do I have to walk the entire scene to build that
> up by querying the bounding box for every geometry in the scene ?
> > >
> > > Any sample code I can view to get me going ?
> > >
> > > ```
> > >
> /****************************************************************************
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> ****************************************************************************/
> > >
> > > #include <QFileDialog>
> > > #include <QApplication>
> > >
> > > #include <Qt3DRender/QCamera>
> > > #include <Qt3DCore/QEntity>
> > > #include <Qt3DCore/QAspectEngine>
> > > #include <Qt3DInput/QInputAspect>
> > > #include <Qt3DRender/QSceneLoader>
> > > #include <Qt3DRender/QRenderAspect>
> > > #include <Qt3DExtras/QForwardRenderer>
> > > #include <Qt3DExtras/qt3dwindow.h>
> > > // #include <Qt3DExtras/qfirstpersoncameracontroller.h>
> > > #include "MyCameraController.h"
> > > #include "TrackballCameraController.h"
> > >
> > > class SceneWalker : public QObject
> > > {
> > > public:
> > > SceneWalker(Qt3DRender::QSceneLoader *loader) : m_loader(loader) {
> }
> > >
> > > void onStatusChanged();
> > >
> > > private:
> > > void walkEntity(Qt3DCore::QEntity *e, int depth = 0);
> > >
> > > Qt3DRender::QSceneLoader *m_loader;
> > > };
> > >
> > > void SceneWalker::onStatusChanged()
> > > {
> > > qDebug() << "Status changed:" << m_loader->status();
> > > if (m_loader->status() != Qt3DRender::QSceneLoader::Ready)
> > > return;
> > >
> > > // The QSceneLoader instance is a component of an entity. The
> loaded scene
> > > // tree is added under this entity.
> > > QVector<Qt3DCore::QEntity *> entities = m_loader->entities();
> > >
> > > // Technically there could be multiple entities referencing the
> scene loader
> > > // but sharing is discouraged, and in our case there will be one
> anyhow.
> > > if (entities.isEmpty())
> > > return;
> > > Qt3DCore::QEntity *root = entities[0];
> > > // Print the tree.
> > > walkEntity(root);
> > >
> > > // To access a given node (like a named mesh in the scene), use
> QObject::findChild().
> > > // The scene structure and names always depend on the asset.
> > > Qt3DCore::QEntity *e = root->findChild<Qt3DCore::QEntity
> *>(QStringLiteral("PlanePropeller_mesh")); // toyplane.obj
> > > if (e)
> > > qDebug() << "Found propeller node" << e << "with components"
> << e->components();
> > > }
> > >
> > > void SceneWalker::walkEntity(Qt3DCore::QEntity *e, int depth)
> > > {
> > > Qt3DCore::QNodeVector nodes = e->childNodes();
> > > for (int i = 0; i < nodes.count(); ++i) {
> > > Qt3DCore::QNode *node = nodes[i];
> > > Qt3DCore::QEntity *entity = qobject_cast<Qt3DCore::QEntity
> *>(node);
> > > if (entity) {
> > > QString indent;
> > > indent.fill(' ', depth * 2);
> > > qDebug().noquote() << indent << "Entity:" << entity <<
> "Components:" << entity->components();
> > > walkEntity(entity, depth + 1);
> > > }
> > > }
> > > }
> > >
> > > int main(int ac, char **av)
> > > {
> > > QApplication app(ac, av);
> > > Qt3DExtras::Qt3DWindow view;
> > > view.defaultFrameGraph()->setClearColor(Qt::black);
> > >
> > > // Root entity
> > > Qt3DCore::QEntity *sceneRoot = new Qt3DCore::QEntity();
> > >
> > > // Scene Camera
> > > Qt3DRender::QCamera *camera = view.camera();
> > >
> camera->setProjectionType(Qt3DRender::QCameraLens::PerspectiveProjection);
> > > camera->setViewCenter(QVector3D(0.0f, 3.5f, 0.0f));
> > > camera->setPosition(QVector3D(0.0f, 3.5f, 25.0f));
> > > camera->setNearPlane(0.001f);
> > > camera->setFarPlane(10000.0f);
> > >
> > > // For camera controls
> > > // Qt3DExtras::QFirstPersonCameraController *camController = new
> Qt3DExtras::QFirstPersonCameraController(sceneRoot);
> > > TrackballCameraController *camController = new
> TrackballCameraController(sceneRoot);
> > > camController->setWindowSize(QSize(view.width(),view.height()));
> //
> https://github.com/cjmdaixi/Qt3DTrackball/issues/1#issuecomment-544183228
> > > camController->setCamera(camera);
> > >
> > > // Scene loader
> > > Qt3DCore::QEntity *sceneLoaderEntity = new
> Qt3DCore::QEntity(sceneRoot);
> > > Qt3DRender::QSceneLoader *sceneLoader = new
> Qt3DRender::QSceneLoader(sceneLoaderEntity);
> > > SceneWalker sceneWalker(sceneLoader);
> > > QObject::connect(sceneLoader,
> &Qt3DRender::QSceneLoader::statusChanged, &sceneWalker,
> &SceneWalker::onStatusChanged);
> > > sceneLoaderEntity->addComponent(sceneLoader);
> > >
> > > QStringList args = QCoreApplication::arguments();
> > > QUrl sourceFileName;
> > > if (args.count() <= 1) {
> > > QWidget *container = new QWidget();
> > > QFileDialog dialog;
> > > dialog.setFileMode(QFileDialog::AnyFile);
> > > sourceFileName = dialog.getOpenFileUrl(container,
> QStringLiteral("Open a scene file"));
> > > } else {
> > > sourceFileName = QUrl::fromLocalFile(args[1]);
> > > }
> > >
> > > if (sourceFileName.isEmpty())
> > > return 0;
> > >
> > > sceneLoader->setSource(sourceFileName);
> > >
> > > view.setRootEntity(sceneRoot);
> > > view.show();
> > >
> > > return app.exec();
> > > }
> > > ```
> > >
> > > Cheers
> > > --
> > > Nicholas Yue
> > > https://www.linkedin.com/in/nicholasyue/
> > > _______________________________________________
> > > Interest mailing list
> > > Interest at qt-project.org
> > > https://lists.qt-project.org/listinfo/interest
> >
> > —
> > Mike Krus | mike.krus at kdab.com | Senior Software Engineer & Teamlead
> > KDAB (UK) Ltd., a KDAB Group company
> > Tel: UK Office +44 1625 809908 Mobile +44 7833 491941
> > KDAB - The Qt Experts, C++, OpenGL Experts
> >
> >
> >
> >
> > --
> > Nicholas Yue
> > https://www.linkedin.com/in/nicholasyue/
>
> —
> Mike Krus | mike.krus at kdab.com | Senior Software Engineer & Teamlead
> KDAB (UK) Ltd., a KDAB Group company
> Tel: UK Office +44 1625 809908 Mobile +44 7833 491941
> KDAB - The Qt Experts, C++, OpenGL Experts
>
>
>
--
Nicholas Yue
https://www.linkedin.com/in/nicholasyue/
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