Qt3D picking triangles

RLayman

I've been trying to get triangle data for a good while now using Qt3D in C++ with no success. I have been able to get the PickEvent to work and it's data is correct but I don't know how to get the PickTriangleEvent. I've search all over the place but was only able to find one example on getting the triangle data and it was in QML - when I tried the same thing in C++ it didn't work.

Currently, this is how I'm getting the PickEvent data.

I add the QObjectPicker component to the mesh object.
connect the signal

connect(m_pObjectPicker,SIGNAL(clicked(Qt3DRender::QPickEvent*)),this,SLOT(clicked(Qt3DRender::QPickEvent*)));

The clicked slot looks like this:

void Mesh::clicked(Qt3DRender::QPickEvent* event){ ... }

My pick settings are already set to triangles:

m_pFrameGraph->pickingSettings()->setPickMethod(Qt3DRender::QPickingSettings::TrianglePicking);
m_pFrameGraph->pickingSettings()->setPickResultMode(Qt3DRender::QPickingSettings::AllPicks);

And this all works fine except when trying to get the triangle data.

m3g1dd

@RLayman I had the same problem, I had this method to add Qt3DRender::QObjectPicker to my entities:

Qt3DRender::QObjectPicker *EditorScene::createObjectPickerForEntity(Qt3DCore::QEntity *entity)
{
    Qt3DRender::QObjectPicker *picker = new Qt3DRender::QObjectPicker(entity);
    entity->addComponent(picker);
    connect(picker, &Qt3DRender::QObjectPicker::pressed, this, &EditorScene::handlePickerPress);
return picker;
}

My rendering settings Qt3DRender::QRenderSettings are added to entities like this, note that the PickMethod must be TrianglePicking:

m_renderSettings = new Qt3DRender::QRenderSettings();
    m_renderSettings->pickingSettings()->setPickMethod(Qt3DRender::QPickingSettings::TrianglePicking);
    m_renderSettings->pickingSettings()->setPickResultMode(Qt3DRender::QPickingSettings::NearestPick);

entity->addComponent(m_renderSettings);

And I had this code to handle click press events I was able to print click position/location by event->worldIntersection() but i didn't know how to get the index of clicked triangle. Finally, I managed to print the index of clicked triangle by casting Qt3DRender::QPickEvent * as Qt3DRender::QPickTriangleEvent *:

void EditorScene::handlePickerPress(Qt3DRender::QPickEvent *event)
{
    // // "event" will give me clicked coordinates like this:
    qDebug() << __func__ << ": global Coord: " << event->worldIntersection();
    
    // // Also I can get picked/clicked triangle index and its vertices by casting event pointer type:
    Qt3DRender::QPickTriangleEvent *eventTri = static_cast<Qt3DRender::QPickTriangleEvent *>(event);
    qDebug() << __func__ << "Pick Triangle Index: " << eventTri->triangleIndex();
    qDebug() << __func__ << "Pick Triangle Vertex 1: " << eventTri->vertex1Index();
    qDebug() << __func__ << "Pick Triangle Vertex 2: " << eventTri->vertex2Index();
    qDebug() << __func__ << "Pick Triangle Vertex 3: " << eventTri->vertex3Index();
}

unclejimbo 0

@m3g1dd Hi, is your QGeometryRenderer component a built-in mesh in Qt3SDExtras or is it a custom mesh?

I've got some troubles picking triangles for a custom mesh built from QGeometry, QAttribute and QBuffer. The clicked event never trigers. But when I use a built-in mesh like QSphereMesh it works fine. Any idea how to do triangle picking for custom meshes?

m3g1dd

@unclejimbo-0 Hello. My Entity is imported with Qt3DRender::QSceneLoader like this:

m_sceneLoaderEntity = new Qt3DCore::QEntity();

 Qt3DRender::QSceneLoader *sceneLoader = new Qt3DRender::QSceneLoader(m_sceneLoaderEntity);

// EditorSceneItemModel::handleImportEntityLoaderStatusChanged is a slot developed to react to a signal when import operation is finished
QObject::connect(sceneLoader, &Qt3DRender::QSceneLoader::statusChanged,
                     this, &EditorSceneItemModel::handleImportEntityLoaderStatusChanged);

sceneLoader->setSource(fileUrl);

m_sceneLoaderEntity->addComponent(sceneLoader);

So, it might be considered as custom mesh! I think picking triangles should work fine with custom meshes. By the way, I'm working with Qt 5.11.2