[Interest] Qt3D : QSceneLoader - determining scene level geometry bounding box
Mike Krus
mike.krus at kdab.com
Tue Aug 2 14:55:58 CEST 2022
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/
> _______________________________________________
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> 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
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