[Interest] Qt3D : QSceneLoader - determining scene level geometry bounding box
Mike Krus
mike.krus at kdab.com
Wed Aug 3 10:25:45 CEST 2022
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
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