[Interest] Qt3D : QSceneLoader - determining scene level geometry bounding box
Nicholas Yue
yue.nicholas at gmail.com
Fri Aug 5 21:38:33 CEST 2022
Any insight ?
On Wed, 3 Aug 2022 at 15:44, Nicholas Yue <yue.nicholas at gmail.com> wrote:
> 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/
>
--
Nicholas Yue
https://www.linkedin.com/in/nicholasyue/
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