[Interest] Qt3D - QObjectPicker doesn't work with multiple QLayers and QLayerFilters

Sakthi G sakthi.g at vjcs.com
Thu Aug 22 21:23:16 CEST 2024


Hello,
	Yes, in our case, the objects are rendered in same viewport and camera with only difference being layer filters. I also tried setting the parent after creating the entity, it didn't work. 

	In our application, each sub entity already has separate parent with root entity being the grandparent of all, and the layer component is added to the parent entity. I tried all combinations of adding layer to entities, only the first filtered layer is properly pickable in all scenarios.

	As you suggested, I created a small example and in it, I have successfully reproduced this bug. I have attached the project in QTBUG-128299, and assigned it to you. But I will paste the code here for reference:

//main.cpp

#include <QGuiApplication>

#include <Qt3DCore/qentity.h>
#include <Qt3DCore/qtransform.h>

#include <QtWidgets/QApplication>
#include <QtWidgets/QWidget>
#include <QtWidgets/QHBoxLayout>
#include <QtGui/QScreen>

#include <Qt3DRender/QRenderSurfaceSelector>
#include <Qt3DRender/qpointlight.h>
#include <Qt3DRender/QViewport>
#include <Qt3DRender/QObjectPicker>
#include <Qt3DRender/QNoDraw>
#include <Qt3DRender/QCameraSelector>
#include <Qt3DRender/QRenderStateSet>
#include <Qt3DRender/QLayerFilter>
#include <Qt3DRender/QDepthTest>
#include <Qt3DRender/QCullFace>
#include <Qt3DRender/QLayer>
#include <Qt3DRender/qcamera.h>
#include <Qt3DRender/qcameralens.h>

#include <Qt3DExtras/QSphereMesh>
#include <Qt3DExtras/qforwardrenderer.h>
#include <Qt3DExtras/QPhongMaterial>
#include <Qt3DExtras/qt3dwindow.h>
#include <Qt3DExtras/qfirstpersoncameracontroller.h>

#include <QApplication>

int main(int argc, char *argv[])
{
    // I exclusively use opengl in my app but it has the same issue with QRhi.
    /*
    bool envvar = qputenv("QT3D_RENDERER", "opengl");
    qDebug() << "Opengl Environment variable set:" << envvar;

    QSurfaceFormat format = QSurfaceFormat::defaultFormat();
    format.setDepthBufferSize(24);
    format.setStencilBufferSize(8);
    format.setSamples(4);
    format.setVersion(3, 3);
    format.setProfile(QSurfaceFormat::CoreProfile);
    QSurfaceFormat::setDefaultFormat(format);
    */
    QApplication app(argc, argv);
    Qt3DExtras::Qt3DWindow *view = new Qt3DExtras::Qt3DWindow();
    view->defaultFrameGraph()->setClearColor(QColor(QRgb(0x4d4d4f)));
    QWidget *container = QWidget::createWindowContainer(view);
    QSize screenSize = view->screen()->size();
    container->setMinimumSize(QSize(200, 100));
    container->setMaximumSize(screenSize);

    QWidget *widget = new QWidget;
    QHBoxLayout *hLayout = new QHBoxLayout(widget);
    QVBoxLayout *vLayout = new QVBoxLayout();
    vLayout->setAlignment(Qt::AlignTop);
    hLayout->addWidget(container, 1);
    hLayout->addLayout(vLayout);

    widget->setWindowTitle(QStringLiteral("QObjectPicker bug"));

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

    Qt3DRender::QCamera *cameraEntity = view->camera();

    cameraEntity->lens()->setPerspectiveProjection(45.0f, 16.0f/9.0f, 0.1f, 1000.0f);
    cameraEntity->setPosition(QVector3D(0, 0, 20.0f));
    cameraEntity->setUpVector(QVector3D(0, 1, 0));
    cameraEntity->setViewCenter(QVector3D(0, 0, 0));

    Qt3DCore::QEntity *lightEntity = new Qt3DCore::QEntity(rootEntity);
    Qt3DRender::QPointLight *light = new Qt3DRender::QPointLight(lightEntity);
    light->setColor("white");
    light->setIntensity(1);
    lightEntity->addComponent(light);
    Qt3DCore::QTransform *lightTransform = new Qt3DCore::QTransform(lightEntity);
    lightTransform->setTranslation(cameraEntity->position());
    lightEntity->addComponent(lightTransform);

    Qt3DExtras::QFirstPersonCameraController *camController = new Qt3DExtras::QFirstPersonCameraController(rootEntity);
    camController->setCamera(cameraEntity);

    Qt3DRender::QLayer* opaqueLayer = new Qt3DRender::QLayer;
    opaqueLayer->setRecursive(true);
    opaqueLayer->setObjectName("Opaque Layer");

    Qt3DRender::QLayer* transparentLayer = new Qt3DRender::QLayer;
    transparentLayer->setRecursive(true);
    transparentLayer->setObjectName("Transparent Layer");

    // Framegraph starts here
    auto renderSurfaceSelector = new Qt3DRender::QRenderSurfaceSelector;
    renderSurfaceSelector->setSurface(view);

    Qt3DRender::QClearBuffers* clearBuffers = new Qt3DRender::QClearBuffers(renderSurfaceSelector);
    clearBuffers->setBuffers(Qt3DRender::QClearBuffers::AllBuffers);
    clearBuffers->setClearColor(Qt::gray);
    Qt3DRender::QNoDraw* noDraw = new Qt3DRender::QNoDraw(clearBuffers);

    Qt3DRender::QViewport* mainViewport = new Qt3DRender::QViewport(renderSurfaceSelector);
    mainViewport->setNormalizedRect(QRectF(0, 0, 1.0, 1.0));

    Qt3DRender::QCameraSelector* cameraSelector = new Qt3DRender::QCameraSelector(mainViewport);
    cameraSelector->setCamera(view->camera());

    Qt3DRender::QRenderStateSet* renderStateSet = new Qt3DRender::QRenderStateSet(cameraSelector);
    {
        Qt3DRender::QDepthTest* depthTest = new Qt3DRender::QDepthTest;
        depthTest->setDepthFunction(Qt3DRender::QDepthTest::LessOrEqual);
        renderStateSet->addRenderState(depthTest);

        Qt3DRender::QCullFace* cullFace = new Qt3DRender::QCullFace(renderStateSet);
        cullFace->setMode(Qt3DRender::QCullFace::NoCulling);
        renderStateSet->addRenderState(cullFace);
    }

    // Opaque branch - try reversing with layerFilterTransparent. Change order of both filters to reverse them.
    Qt3DRender::QLayerFilter* layerFilterOpaque = new Qt3DRender::QLayerFilter(renderStateSet);
    layerFilterOpaque->addLayer(opaqueLayer);

    // Transparent branch - try reversing with layerFilterOpaque
    Qt3DRender::QLayerFilter* layerFilterTransparent = new Qt3DRender::QLayerFilter(renderStateSet);
    layerFilterTransparent->addLayer(transparentLayer);

    view->setActiveFrameGraph(renderSurfaceSelector);
    view->setRootEntity(rootEntity);

    Qt3DCore::QEntity* redSphereEntity = new Qt3DCore::QEntity(rootEntity);
    Qt3DExtras::QPhongMaterial* redSphereMaterial = new Qt3DExtras::QPhongMaterial();
    {
        Qt3DExtras::QSphereMesh* sphereMesh = new Qt3DExtras::QSphereMesh();
        sphereMesh->setRadius(3.0f);
        sphereMesh->setRings(10);
        Qt3DCore::QTransform* sphereTransform = new Qt3DCore::QTransform();
        sphereTransform->setTranslation(QVector3D(-10.0f, 0.0f, 0.0f));

        redSphereMaterial->setDiffuse(Qt::red);
        Qt3DRender::QObjectPicker* subEntitypicker = new Qt3DRender::QObjectPicker;
        QObject::connect(subEntitypicker, &Qt3DRender::QObjectPicker::clicked, [redSphereMaterial](){
            qDebug() << "Red Picked";
            if (redSphereMaterial->diffuse() == Qt::red)
            {
                redSphereMaterial->setDiffuse(Qt::yellow);
            }
            else
            {
                redSphereMaterial->setDiffuse(Qt::red);
            }
        });
        redSphereEntity->addComponent(sphereMesh);
        redSphereEntity->addComponent(sphereTransform);
        redSphereEntity->addComponent(subEntitypicker);
        redSphereEntity->addComponent(redSphereMaterial);
        redSphereEntity->addComponent(opaqueLayer);
    }

    Qt3DCore::QEntity* blueSphereEntity = new Qt3DCore::QEntity(rootEntity);
    Qt3DExtras::QPhongMaterial* blueSphereMaterial = new Qt3DExtras::QPhongMaterial();
    {
        Qt3DExtras::QSphereMesh* sphereMesh = new Qt3DExtras::QSphereMesh();
        sphereMesh->setRadius(3.0f);
        sphereMesh->setRings(10);
        Qt3DCore::QTransform* sphereTransform = new Qt3DCore::QTransform();
        sphereTransform->setTranslation(QVector3D(10.0f, 0.0f, 0.0f));
        Qt3DRender::QObjectPicker* subEntitypicker = new Qt3DRender::QObjectPicker;
        blueSphereMaterial->setDiffuse(Qt::blue);
        QObject::connect(subEntitypicker, &Qt3DRender::QObjectPicker::clicked, [blueSphereMaterial](){
            qInfo() << "Blue Picked";
            if (blueSphereMaterial->diffuse() == Qt::blue)
            {
                blueSphereMaterial->setDiffuse(Qt::yellow);
            }
            else
            {
                blueSphereMaterial->setDiffuse(Qt::blue);
            }
        });
        blueSphereEntity->addComponent(sphereMesh);
        blueSphereEntity->addComponent(subEntitypicker);
        blueSphereEntity->addComponent(sphereTransform);
        blueSphereEntity->addComponent(blueSphereMaterial);
        blueSphereEntity->addComponent(transparentLayer);
    }

    qDebug() << "Try to click red and blue sphere. Red has first filtered layer as component and blue has second filtered layer as component";
    qDebug() << "When picked, spheres change color. You will notice blue cannot be picked as it has second filtered layer in framegraph";
    qDebug() << "You can try reversing the order of layer filter nodes in framegraph to see the other sphere picked";
    // Show window
    widget->show();
    widget->resize(1200, 800);

    return app.exec();
}

// End of main.cpp

#CMakeLists.txt

cmake_minimum_required(VERSION 3.14)

project(sample_test LANGUAGES CXX)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 REQUIRED COMPONENTS 3DCore 3DExtras 3DInput 3DRender Core Gui Widgets)


add_executable(sample_test
  main.cpp
)
target_link_libraries(sample_test
    Qt6::3DCore
    Qt6::3DExtras
    Qt6::3DInput
    Qt6::3DRender
    Qt6::Core
    Qt6::Gui
    Qt6::Widgets
)

include(GNUInstallDirs)
install(TARGETS sample_test
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

# End of CMakeLists.txt

	In this simple example, picking doesn't work for the transparentLayer, but it works for opaqueLayer. Hope to find a solution for this as using multiple QLayerFilters seems to be the only way to handle transparency correctly. If there is an alternative way to achieve perfect transparency(which is not possible in QSortPolicy), please let me know. Thanks.

Regards,
Sakthi
Sakthi.g at vjcs.com

-----Original Message-----
From: Mike Krus [mailto:mike.krus at kdab.com] 
Sent: 22 August 2024 20:49
To: sakthi.g at vjcs.com
Cc: interest at qt-project.org
Subject: Re: [Interest] Qt3D - QObjectPicker doesn't work with multiple QLayers and QLayerFilters

Hi

the frame affects picking in a couple of ways:
- the layer filter, entities should only be pickable if the filter accepts the entities, otherwise they would be ignored
- the camera and viewport that are active in the branch (this affect the picking ray that gets tested)

I’m assuming in your case the only difference is the layer filter?

If seems like there may be an issue with the dynamic nature of your scene graph and 
Qt3D’s backend not being updated properly.

A few things to try:
- when creating new entities, create them without a parent, add the components and children, then set the parent
- if possible with your scene graph, maybe have separate parents for opaque and transparent entities (rather than
  mixing them under the same parent), and add the layer component to the parent entities rather then each entity
  (making sure you mark it as recursive).

I don’t think these should change the issue but might be something worth trying.

If you have a small example I can use to reproduce the issue, please create a bug report and assign it to me.


Mike


> On 22 Aug 2024, at 14:19, Sakthi G <sakthi.g at vjcs.com> wrote:
> 
> Hello, We have a Qt3D application where we have multiple QLayers for different types of meshes. We have found out that QObjectPicker doesn’t work properly with multiple QLayers. It doesn’t get triggered consistently if the entity has layer component which is not filtered at the top of the framegraph.
>  Consider the following simplified framegraph with two layer filter branches, one for opaque and one for transparent objects:
>    Qt3DRender::QViewport* mainViewport = new Qt3DRender::QViewport(renderSurfaceSelector);
>         mainViewport->setNormalizedRect(QRectF(0, 0, 1.0, 1.0));
>          Qt3DRender::QCameraSelector* cameraSelector = new Qt3DRender::QCameraSelector(mainViewport);
>         cameraSelector->setCamera(view->camera());
>          Qt3DRender::QRenderStateSet* renderStateSet = new Qt3DRender::QRenderStateSet(cameraSelector);
>         {
>         Qt3DRender::QDepthTest* depthTest = new Qt3DRender::QDepthTest;
>         depthTest->setDepthFunction(Qt3DRender::QDepthTest::LessOrEqual);
>         renderStateSet->addRenderState(depthTest);
>          Qt3DRender::QCullFace* cullFace = new Qt3DRender::QCullFace(renderStateSet);
>         cullFace->setMode(Qt3DRender::QCullFace::NoCulling);
>         renderStateSet->addRenderState(cullFace);
>   }
>   // Opaque branch
>         Qt3DRender::QLayerFilter* layerFilterOpaque = new Qt3DRender::QLayerFilter(renderStateSet);
>         layerFilterOpaque->addLayer(opaqueLayer);
>         // Transparent branch
>         Qt3DRender::QLayerFilter* layerFilterTransparent = new Qt3DRender::QLayerFilter(renderStateSet);
>         layerFilterTransparent->addLayer(transparentLayer);
>  When we dynamically add meshes to the scene, we check if the default material is transparent and assign the respective layers like this:
>   if (transparent)
>         {
>             entity->addComponent(transparentLayer);               
>         }
>         else
>         {
>             entity->addComponent(opaqueLayer);               
>         }
>  After this, when we click on the dynamically added mesh, only entities with opaqueLayer get triggered 100% of time, entities with transparentLayer gets triggered inconsistently, and sometimes, it gets triggered if we click the backface of the mesh. The hit ratio is around 20%.
>  If we swap the order of layer filters in framegraph, the transparentLayer entities get triggered 100% of time and the opaqueLayer entities get triggered inconsistently. So we think that it is the framegraph which is causing this problem.  But if we modify a material and change the layers of an existing entity(with opaqueLayer), QObjectPicker gets triggered all the time. The following code demonstrates how we do that:
>  pickedEntity->addComponent(transparentLayer);
> pickedEntity->removeComponent(opaqueLayer);
> pickedEntity->setEnabled(false);
> pickedEntity->setEnabled(true);
>  Additionally, we also found that if the same scene with the above mentioned framegraph only contains dynamically created entities with transparentLayer as a component, QObjectPicker is not triggered at all.  How to fix this issue? Why does it work if we modify the layer after creating it with opaqueLayer, but not when adding dynamically while creating? Does QObjectPicker depend on how we setup the framegraph? We couldn’t find any documentation/code/forum posts linking QLayer/QLayerFilter with QObjectPicker. Your help is truly appreciated.
>  Regards,
> Sakthi
> Sakthi.g at vjcs.com
>  ********************************************************************************************************************************************************************
> This e-mail is confidential and is used for VJCS official communication.
> It may also be legally privileged. If you have received this message in error, please delete all copies of it from your system and
> notify the sender by return e-mail. If you are not intended recipient, you may not copy, print, forward,
> disclose or use any part of it. This message has been scanned for viruses and dangerous content by VJCS Mail Scanner,
> and is believed to be clean.
> 
> Visit us at http://secure-web.cisco.com/1gKXHHqznXVDZtWHSNdeBcbzfRW3ws2Ig6-B4Y15r23jAbzQM-yN-zaiKcJejW4T5NUCb1IBRBDfD0f1frDnPAqJFJROoh9dujbh3P1OAJ4scri8qEC6kZqI37jBEh0GXaLy0eo7NGkY57Tw2tNATID1WL-7dw7uvHGvLPpcU0HjWMnB0fabAlDLm7JPWEugUxoPjLO0Jb_GsNa0MsHetCYSnKpg-S8g4FJZntKTY3dntnc-723tdxD-LCA_YnH5LAopjw25qBZqMJR3li-FFEMdOmt4aKotUks9WgJ9raQxcs3xlPA-DwOVR3VjIAQ7_EifbxSjEp10UY6nzOtQ76utS0b1aDyoyAba9zB0OHhgCN_CL8FxddEUuOSmC_wxRw7QNcR9rk68VacwOHiDA6TjWNjC0W_0HolbMMkGi9_1L2CogGB-8wXBJ8Ay3xjh96dbQN9OOdqsU6UOcOPr85A/http%3A%2F%2Fwww.vjcs.com
> ******************************************************************************************************************************************************************** _______________________________________________
> Interest mailing list
> Interest at qt-project.org
> https://secure-web.cisco.com/1DWWEgJDY2stMfXDAHtDgQRIBR8Of7DjVPbJ_ASBzARmvTciTCgVaISHUggLHRTDlNFJ2IB0GJeAKNuv0z2W4g7vXeI5oGMcIa0pHj2DePwYOvMCt2UUpNgwZs3L7hG4pZuV5swDU-nN12eZSc42pSW9jRMJ9cdR2yNCagPXYINI3HKum_SdNrjhQOxbVHXiddr7khguH-HUlPCIJucoilQA9HCg3pM-iFecyUgcizXY0Nr9JM5eCuVlKW8T8dtAtUB8hyFklmLXq12HQTcpw6YJf_voNrU_Isc9A4IJCiqBMnpxJC82WonpU_2WHhNUZnnNOWSdwymJCEeIE6aSGlQX-4n367sr1-Csh4e23QmHZ5ITWzjup6oFRsX0cPBDcJaBIMytADVPcYlgZQJZJibaSTVfOMxn81MSPK9YB_yPiJIBvM30U4TntxzTWSAtJle_avlLnXCZgvHwV3xa-Ug/https%3A%2F%2Flists.qt-project.org%2Flistinfo%2Finterest


—
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


********************************************************************************************************************************************************************
This e-mail is confidential and is used for VJCS official communication.
It may also be legally privileged. If you have received this message in error, please delete all copies of it from your system and
notify the sender by return e-mail. If you are not intended recipient, you may not copy, print, forward,
disclose or use any part of it. This message has been scanned for viruses and dangerous content by VJCS Mail Scanner,
and is believed to be clean.

Visit us at www.vjcs.com
********************************************************************************************************************************************************************


More information about the Interest mailing list