Qt3D: QObjectPicker test not working as expected

drobole

Hi,

I'm trying to make picking work with a simple C++ widget application, using QtCreator 4.2.1 and Qt 5.8.0

The example creates two spheres, a green one at 0,0,0 and a red one at -20, 0, 0

No matter where I click in the 3D space, the green one is hit by the picker ray, no matter what.

However, if I rotate the scene so that the red sphere is exactly in front of the green sphere, the ray hits the red one. Again, no matter what or where I click.

Basically, it seems that the ray always goes from the camera to origo (0,0,0) regardless of where I click with the mouse.

Any tips out there on what I'm forgetting, or doing wrong?

Here is the .cpp file of the example:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <Qt3DCore/QEntity>
#include <Qt3DRender/QCamera>
#include <Qt3DRender/QCameraLens>
#include <Qt3DRender/QRenderSettings>
#include <Qt3DRender/QObjectPicker>
#include <Qt3DExtras/QForwardRenderer>
#include <Qt3DExtras/Qt3DWindow>
#include <Qt3DExtras/QOrbitCameraController>
#include <Qt3DExtras/QSphereMesh>
#include <Qt3DCore/QTransform>
#include <Qt3DExtras/QPhongMaterial>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);


    Qt3DExtras::Qt3DWindow *mView = new Qt3DExtras::Qt3DWindow();
    QWidget *mContainerScene = QWidget::createWindowContainer(mView, this);
    ui->layoutScene->addWidget(mContainerScene);

    Qt3DRender::QCamera *mCamera = mView->camera();
    mCamera->setProjectionType(Qt3DRender::QCameraLens::PerspectiveProjection);
    //mCamera->setAspectRatio(mView->width() / mView->height());
    mCamera->setAspectRatio(16.0f / 9.0f);
    mCamera->setFieldOfView(45.0f);
    mCamera->setUpVector(QVector3D(0.0f, 1.0f, 0.0f));
    mCamera->setPosition(QVector3D(0.0f, 20.0f, 80.0f));
    mCamera->setViewCenter(QVector3D(0.0f, 0.0f, 0.0f));
    mCamera->setNearPlane(0.01f);
    mCamera->setFarPlane(100000.0f);

    mView->defaultFrameGraph()->setClearColor(QColor(0, 0, 0));

    Qt3DRender::QRenderSettings *mRenderSettings = new Qt3DRender::QRenderSettings();
    mRenderSettings->pickingSettings()->setPickMethod(Qt3DRender::QPickingSettings::TrianglePicking);
    mRenderSettings->pickingSettings()->setPickResultMode(Qt3DRender::QPickingSettings::NearestPick);
    mRenderSettings->setActiveFrameGraph(mView->defaultFrameGraph());

    Qt3DCore::QEntity *mSceneEntity = new Qt3DCore::QEntity();
    mSceneEntity->addComponent(mRenderSettings);
    mSceneEntity->setObjectName(QStringLiteral("scene entity"));

    Qt3DExtras::QOrbitCameraController *mCameraController =
            new Qt3DExtras::QOrbitCameraController(mSceneEntity);
    mCameraController->setLinearSpeed(50.0f);
    mCameraController->setLookSpeed(180.0f);
    mCameraController->setCamera(mCamera);

    // Create entity 1
    Qt3DCore::QEntity *entity1 = new Qt3DCore::QEntity(mSceneEntity);
    entity1->setObjectName("entity 1");

    Qt3DExtras::QSphereMesh *mMesh1 = new Qt3DExtras::QSphereMesh(entity1);
    mMesh1->setRadius(1.0f);
    entity1->addComponent(mMesh1);

    Qt3DCore::QTransform *mTransform1 = new Qt3DCore::QTransform(entity1);
    mTransform1->setTranslation(QVector3D(0, 0, 0));
    mTransform1->setScale(1);
    mTransform1->setScale3D(QVector3D(1, 1, 1));
    entity1->addComponent(mTransform1);

    Qt3DExtras::QPhongMaterial *mMaterial1 = new Qt3DExtras::QPhongMaterial(entity1);
    QColor color(0, 255, 0);
    mMaterial1->setDiffuse(color);
    mMaterial1->setSpecular(color);
    mMaterial1->setAmbient(color);
    mMaterial1->setShininess(5.0f);
    entity1->addComponent(mMaterial1);

    Qt3DRender::QObjectPicker *picker1 = new Qt3DRender::QObjectPicker(entity1);
    picker1->setHoverEnabled(false);
    picker1->setEnabled(true);
    QObject::connect(picker1, &Qt3DRender::QObjectPicker::pressed, this, &MainWindow::onPicked);
    entity1->addComponent(picker1);

    // Create entity 2
    Qt3DCore::QEntity *entity2 = new Qt3DCore::QEntity(mSceneEntity);
    entity2->setObjectName("entity 2");

    Qt3DExtras::QSphereMesh *mMesh2 = new Qt3DExtras::QSphereMesh(entity2);
    mMesh2->setRadius(1.0f);
    entity2->addComponent(mMesh2);

    Qt3DCore::QTransform *mTransform2 = new Qt3DCore::QTransform(entity2);
    mTransform2->setTranslation(QVector3D(-20, 0, 0));
    mTransform2->setScale(1);
    mTransform2->setScale3D(QVector3D(1, 1, 1));
    entity2->addComponent(mTransform2);

    Qt3DExtras::QPhongMaterial *mMaterial2 = new Qt3DExtras::QPhongMaterial(entity2);
    QColor color2(255, 0, 0);
    mMaterial2->setDiffuse(color2);
    mMaterial2->setSpecular(color2);
    mMaterial2->setAmbient(color2);
    mMaterial2->setShininess(5.0f);
    entity2->addComponent(mMaterial2);

    Qt3DRender::QObjectPicker *picker2 = new Qt3DRender::QObjectPicker(entity2);
    picker2->setHoverEnabled(false);
    picker2->setEnabled(true);
    QObject::connect(picker2, &Qt3DRender::QObjectPicker::pressed, this, &MainWindow::onPicked);
    entity2->addComponent(picker2);

    mView->setRootEntity(mSceneEntity);
    mView->show();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::onPicked(Qt3DRender::QPickEvent *evt)
{
    Qt3DCore::QEntity *entity = qobject_cast<Qt3DCore::QEntity*>(sender()->parent());
    qDebug() << "Picked " << entity->objectName();
}

drobole

Not sure what is going on here but not creating a RenderSetting and not setting the camera aspect ratio and FOW solved the issue.
By creating a custom RenderSettings I may have ended up with a orthogonal projection or something.

Here is a working example:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <Qt3DCore/QEntity>
#include <Qt3DRender/QCamera>
#include <Qt3DRender/QCameraLens>
#include <Qt3DRender/QObjectPicker>
#include <Qt3DExtras/QForwardRenderer>
#include <Qt3DExtras/Qt3DWindow>
#include <Qt3DExtras/QOrbitCameraController>
#include <Qt3DExtras/QSphereMesh>
#include <Qt3DCore/QTransform>
#include <Qt3DExtras/QPhongMaterial>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    Qt3DExtras::Qt3DWindow *view = new Qt3DExtras::Qt3DWindow();
    QWidget *containerScene = QWidget::createWindowContainer(view, this);
    ui->layoutScene->addWidget(containerScene);

    Qt3DRender::QCamera *camera = view->camera();
    camera->setProjectionType(Qt3DRender::QCameraLens::PerspectiveProjection);
    camera->setUpVector(QVector3D(0.0f, 1.0f, 0.0f));
    camera->setPosition(QVector3D(0.0f, 20.0f, 80.0f));
    camera->setViewCenter(QVector3D(0.0f, 0.0f, 0.0f));

    view->defaultFrameGraph()->setClearColor(QColor(0, 0, 0));

    Qt3DCore::QEntity *sceneEntity = new Qt3DCore::QEntity();

    Qt3DExtras::QOrbitCameraController *cameraController =
            new Qt3DExtras::QOrbitCameraController(sceneEntity);
    cameraController->setLinearSpeed(50.0f);
    cameraController->setLookSpeed(180.0f);
    cameraController->setCamera(camera);

    // Create entity 1
    Qt3DCore::QEntity *entity1 = new Qt3DCore::QEntity(sceneEntity);
    entity1->setObjectName("entity 1");

    Qt3DExtras::QSphereMesh *mesh1 = new Qt3DExtras::QSphereMesh(entity1);
    mesh1->setRadius(1.0f);
    entity1->addComponent(mesh1);

    Qt3DCore::QTransform *transform1 = new Qt3DCore::QTransform(entity1);
    transform1->setTranslation(QVector3D(0, 0, 0));
    transform1->setScale(1);
    transform1->setScale3D(QVector3D(1, 1, 1));
    entity1->addComponent(transform1);

    Qt3DExtras::QPhongMaterial *material1 = new Qt3DExtras::QPhongMaterial(entity1);
    QColor color(0, 255, 0);
    material1->setDiffuse(color);
    material1->setSpecular(color);
    material1->setAmbient(color);
    material1->setShininess(5.0f);
    entity1->addComponent(material1);

    Qt3DRender::QObjectPicker *picker1 = new Qt3DRender::QObjectPicker(entity1);
    picker1->setHoverEnabled(false);
    picker1->setEnabled(true);
    QObject::connect(picker1, &Qt3DRender::QObjectPicker::pressed, this, &MainWindow::onPicked);
    entity1->addComponent(picker1);

    // Create entity 2
    Qt3DCore::QEntity *entity2 = new Qt3DCore::QEntity(sceneEntity);
    entity2->setObjectName("entity 2");

    Qt3DExtras::QSphereMesh *mesh2 = new Qt3DExtras::QSphereMesh(entity2);
    mesh2->setRadius(1.0f);
    entity2->addComponent(mesh2);

    Qt3DCore::QTransform *transform2 = new Qt3DCore::QTransform(entity2);
    transform2->setTranslation(QVector3D(-20, 0, 0));
    transform2->setScale(1);
    transform2->setScale3D(QVector3D(1, 1, 1));
    entity2->addComponent(transform2);

    Qt3DExtras::QPhongMaterial *material2 = new Qt3DExtras::QPhongMaterial(entity2);
    QColor color2(255, 0, 0);
    material2->setDiffuse(color2);
    material2->setSpecular(color2);
    material2->setAmbient(color2);
    material2->setShininess(5.0f);
    entity2->addComponent(material2);

    Qt3DRender::QObjectPicker *picker2 = new Qt3DRender::QObjectPicker(entity2);
    picker2->setHoverEnabled(false);
    picker2->setEnabled(true);
    QObject::connect(picker2, &Qt3DRender::QObjectPicker::pressed, this, &MainWindow::onPicked);
    entity2->addComponent(picker2);

    view->setRootEntity(sceneEntity);
    view->show();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::onPicked(Qt3DRender::QPickEvent *evt)
{
    Qt3DCore::QEntity *entity = qobject_cast<Qt3DCore::QEntity*>(sender()->parent());
    qDebug() << "Picked " << entity->objectName();
}