How to render .obj files from any directory in Qt 5.9

Question

I'm trying to load .obj files into Qt using the Qt3D library. So far I have this code mostly copied from one of the examples:

Qt3DCore::QEntity *createScene()
{
    // Root entity
    Qt3DCore::QEntity *rootEntity = new Qt3DCore::QEntity;

    // Material
    Qt3DRender::QMaterial *material = new Qt3DExtras::QPhongMaterial(rootEntity);

    // Chest Entity
    Qt3DCore::QEntity *chestEntity = new Qt3DCore::QEntity(rootEntity);
    Qt3DRender::QMesh *chestMesh = new Qt3DRender::QMesh(rootEntity);
    chestMesh->setSource(QUrl("qrc:/PT18E.obj"));

    chestEntity->addComponent(chestMesh);
    chestEntity->addComponent(material);

    return rootEntity;
}

int main(int argc, char* argv[])
{
    QGuiApplication app(argc, argv);
    Qt3DExtras::Qt3DWindow view;

    Qt3DCore::QEntity *scene = createScene();

    // Camera
    Qt3DRender::QCamera *camera = view.camera();
    camera->lens()->setPerspectiveProjection(45.0f, 16.0f/9.0f, 0.1f, 1000.0f);
    camera->setPosition(QVector3D(0, 0, 1));
    camera->setViewCenter(QVector3D(0, 0, 0));

    // For camera controls
    Qt3DExtras::QOrbitCameraController *camController = new Qt3DExtras::QOrbitCameraController(scene);
    camController->setLinearSpeed( 10.0f );
    camController->setLookSpeed( 180.0f );
    camController->setCamera(camera);

    view.setRootEntity(scene);
    view.show();

    return app.exec();
}

So far, the application can render the object and display it. However, I had to attach the .obj file to a qrc file in order for it to be able to find and render it. When I try to set the source for the chestMesh using the absolute path from any directory, e.g.,

chestMesh->setSource(QURL(C:/Users/username/Documents/Qt/simple-cpp/PT18E.obj))

it does not work. Nothing gets rendered and I see the error in the console saying

QFSFileEngine::open: No file name specified

I've tried adding the exact same path to a QFile object and use the exists function to see if the path is correct, and sure enough it is. But for some reason the mesh cannot use a source that isn't in a qrc file.

How can I load and render any .obj file from the file system (without having to put it in a qrc) in Qt?

Answer 1

For composing the correct url pointing to the file we can try static call QUrl::fromLocalFile. Or given the above code:

chestMesh->setSource(QUrl::fromLocalFile(winPath2ObjFile));