How to zoom toward a 3D mesh with qt?

Question

I'm using a Wheelevent to Zoom in/out in a QWidget view,in use the event to translate the QCamera, is there a solution from the qt api to move toward a point or zoom with the camera to a specific point? I searched in many sections but did'nt find something useful unfortunately.

Answer 1

Edit: Stefan Reinhardt suggested to use QAbstractCameraController to achieve what you want to do. The example I provided is a quick-and-dirty solution. I agree that using the camera controller is the way intended in Qt3D.

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The Qt3D API doesn't support this directly, but you can implement it easily yourself.

Here is a minimally working example, that should get you started (note, that you have to adjust the upvector, when scrolling past the view center I guess):

main.cpp:

#include <QApplication>
#include "graphicswindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    GraphicsWindow graphicsWindow;
    graphicsWindow.show();
    return a.exec();
}

graphicswindow.h:

#include <Qt3DExtras/Qt3DWindow>
#include <Qt3DCore/QEntity>

class GraphicsWindow : public Qt3DExtras::Qt3DWindow {
public:
    GraphicsWindow();
    void wheelEvent ( QWheelEvent * event ) override;

private:
    Qt3DCore::QEntity *createScene();
};

graphicswindow.cpp:

#include "graphicswindow.h"
#include <QMouseEvent>
#include <QVector3D>
#include <Qt3DRender/QCamera>
#include <Qt3DRender/QMaterial>
#include <Qt3DExtras/QGoochMaterial>
#include <Qt3DExtras/QCuboidMesh>

GraphicsWindow::GraphicsWindow() : Qt3DExtras::Qt3DWindow() {
    // You could also create a dedicated setup method
    Qt3DCore::QEntity *root = createScene();
    setRootEntity(root);
    Qt3DRender::QCamera *camera = this->camera();
    camera->lens()->setPerspectiveProjection(45.0f, 16.0f/9.0f, 0.1f, 1000.0f);
    camera->setPosition(QVector3D(20.0, 20.0, 20.0f));
    camera->setViewCenter(QVector3D(0, 0, 0));
}

void GraphicsWindow::wheelEvent(QWheelEvent *event) {
    QVector3D camPos = this->camera()->position();
    camPos.normalize();
    camPos = this->camera()->position() - QVector3D(event->delta() / 300.f,
                                                event->delta() / 300.f,
                                                event->delta() / 300.f);
    this->camera()->setPosition(camPos);
}


Qt3DCore::QEntity* GraphicsWindow::createScene() {
    Qt3DCore::QEntity *rootEntity = new Qt3DCore::QEntity;

    Qt3DRender::QMaterial *material = new Qt3DExtras::QGoochMaterial(rootEntity);

    //Cube
    Qt3DCore::QEntity *cubeEntity = new Qt3DCore::QEntity(rootEntity);
    Qt3DExtras::QCuboidMesh *cubeMesh = new Qt3DExtras::QCuboidMesh;

    cubeEntity->addComponent(cubeMesh);
    cubeEntity->addComponent(material);

    return rootEntity;
}