Setting same context name in multiple contexts.

fcarney

#include <Qt3DQuickExtras>
#include <Qt3DQuickExtras/qt3dquickwindow.h>
#include <QGuiApplication>
#include <QApplication>

std::vector<Qt3DExtras::Quick::Qt3DQuickWindow*> views;

void generateViews(QApplication &app, int viewcount){
    QSurfaceFormat format;
    format.setAlphaBufferSize(8);

    for(int count=0; count<viewcount; count++){
        Qt3DExtras::Quick::Qt3DQuickWindow* view = new Qt3DExtras::Quick::Qt3DQuickWindow();

        view->setFlag(Qt::SplashScreen);
        view->setFormat(format);

        view->engine()->qmlEngine()->rootContext()->setContextProperty("_window", view);  // problems
        //view->engine()->qmlEngine()->rootContext()->setContextObject(view); // problems
        /*
        // all objects are different, why interaction between objects?
        qInfo() << count;
        qInfo() << view->engine();
        qInfo() << view->engine()->qmlEngine();
        qInfo() << view->engine()->qmlEngine()->rootContext();
        */

        view->setSource(QUrl("qrc:/main.qml"));
        view->show();

        //QObject::connect(view->engine()->qmlEngine(), SIGNAL(quit()), &app, SLOT(quit()));

        views.push_back(view);
    }
}

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);    

    generateViews(app, 2);

    return app.exec();
}

This code is based upon the simple-qml example that comes with Qt-Creator.
The version of Qt is 5.9.7.

The problems is that when I call setContextProperty with "_window" as the name for all contexts then the application locks up. If I don't set this, or set the context to something unique like _window0, _window1, etc. then it will run. I have checked the contexts that are created and they are all unique. I am very confused as to why the context of each window would care about the others.

Is there some sort of global context I should be aware of? Even though the pointers for each windows' contexts are unique?

I need the object as reported to each context to be the same name so I only have to write one QML file that is used on all windows created. If I generate a unique name for each window then I will have to somehow determine what that name is on the QML side.

SGaist

Hi and welcome to devnet,

Just a wild guess, I would check whether there's only one engine/rootContext that is created.

fcarney

Hello!

qInfo() << count;
qInfo() << view->engine();
qInfo() << view->engine()->qmlEngine();
qInfo() << view->engine()->qmlEngine()->rootContext();

When I ran this code it produced all unique pointers:

0
Qt3DCore::Quick::QQmlAspectEngine(0x25780d68)
QQmlEngine(0x25790e98)
QQmlContext(0x257b0348)
1
Qt3DCore::Quick::QQmlAspectEngine(0x25832fd0)
QQmlEngine(0x2583ff78)
QQmlContext(0x611f4f28)

That is what is stumping me. What is common to the contexts?

SGaist

I don't know. Can you also provide the QML file so I can test it on my end ?

fcarney

I should have posted this in the first place:

import QtQuick 2.2 as QQ2
import Qt3D.Core 2.0
import Qt3D.Render 2.0
import Qt3D.Input 2.0
import Qt3D.Extras 2.0

Entity {
    id: sceneRoot

    Camera {
        id: camera
        projectionType: CameraLens.PerspectiveProjection
        fieldOfView: 45
        aspectRatio: 16/9
        nearPlane : 0.1
        farPlane : 1000.0
        position: Qt.vector3d( 0.0, 0.0, -40.0 )
        upVector: Qt.vector3d( 0.0, 1.0, 0.0 )
        viewCenter: Qt.vector3d( 0.0, 0.0, 0.0 )
    }

    /*
    OrbitCameraController {
        camera: camera
    }
    */

    KeyboardDevice {
        id: keyboardSourceDevice
    }

    KeyboardHandler {
        sourceDevice: keyboardSourceDevice
        focus: true
        onEscapePressed: {
            Qt.quit()
        }
        onUpPressed: {
            _window.setY(_window.y - 25)
        }
        onDownPressed: {
            _window.setY(_window.y + 25)
        }
    }

    components: [
        RenderSettings {
            activeFrameGraph: ForwardRenderer {
                //clearColor: Qt.rgba(0, 0.5, 1, 1)
                clearColor: Qt.rgba(0, 0, 0, 0)
                camera: camera
            }
        },
        // Event Source will be set by the Qt3DQuickWindow
        InputSettings { }
    ]

    PhongMaterial {
        id: material
    }

    TorusMesh {
        id: torusMesh
        radius: 5
        minorRadius: 1
        rings: 100
        slices: 20
    }

    Transform {
        id: torusTransform
        scale3D: Qt.vector3d(1.5, 1, 0.5)
        rotation: fromAxisAndAngle(Qt.vector3d(1, 0, 0), 45)
    }

    Entity {
        id: torusEntity
        components: [ torusMesh, material, torusTransform ]
    }

    SphereMesh {
        id: sphereMesh
        radius: 3
    }

    Transform {
        id: sphereTransform
        property real userAngle: 0.0
        matrix: {
            var m = Qt.matrix4x4();
            m.rotate(userAngle, Qt.vector3d(0, 1, 0));
            m.translate(Qt.vector3d(20, 0, 0));
            return m;
        }
    }

    QQ2.NumberAnimation {
        target: sphereTransform
        property: "userAngle"
        duration: 10000
        from: 0
        to: 360

        loops: QQ2.Animation.Infinite
        running: true
    }

    Entity {
        id: sphereEntity
        components: [ sphereMesh, material, sphereTransform ]
    }
}

fcarney

I searched around the internet, but could not find an answer for this question:
Can QML search for an object set by using the setContext commands? Also, is the Window that is created in the C++ already set as a context variable in QML?

SGaist

I don't have 5.9.7 at hand currently but I just tested with 5.12 (self-built) and the two windows are created. Can you test a more recent version of Qt ?

fcarney

Hmmm, I just ran it under 5.11.2 and it fails to run if I set it to create 2 windows. It doesn't matter if I expose the view object via setcontextproperty or not.

It puts out this error a bunch of times:
QThread::start: Failed to create thread (The operation completed successfully.)

SGaist

On what OS are you running that ?

fcarney

Windows 10 Pro
mingw 5.3.0
GeForce 1050 mobile

Can you give me 1 reputation so it doesn't take 600 seconds between posts?

fcarney

I tested the same code on:
Windows 7 Pro
mingw 5.3.0
Qt 5.11.2
GeForce 460

I was able to get 5 instances running at the same time before it started having problems. The more I look at this the more I think a QML based 3D rendering pipeline is going to be heavy handed for what I want to do. I need light weight windows to do 3D in lots of windows. I also think part of the issue on the Windows 10 machine is it has 2 video cards. I think the 3D app was running on the Intel GPU rather than the Nvidia GPU. So GPU affinity I think it partially to blame for it not running more than one instance very well.

So I had a look at QOpenGLWindow. I was able get a simple rotating cube scene running in that window. Then I tested it with 50 windows. It opened all 50 on my geforce 460 just fine. They all ran and could rotate the cube. This first test is for a proof of concept and I needed to know if Qt 3D rendering contexts could scale. Running 50 at the same time tells me it can scale well. I didn't even tell the windows to share resources yet.

SGaist,
Thanks for testing this. For now I am going the route of QOpenGLWindow. It fills my needs. I just won't be able to use the convenience of QML for now. I kind of thought that might be the case so it doesn't surprise me.

Thanks