Why are Qt3D Camera settings different in C++ and QML ?

Diracsbracket

Hi.
I'm trying to learn, with some difficulty, Qt3D.

I have a simple 3D text example written in both C++ and QML, with, what I believe exactly the same parameters.

However, I found out that in QML, the image would be upside down + I had to set the z position of the camera to a much bigger value than in C++.

To correct the orientation, I need to explicitly set the upVector property of the camera to Qt.vector3d( 0.0, -1.0, 0.0 ) in QML.

Why these differences between C++ and QML?

C++ code:

#include <QCoreApplication>
#include <Qt3DCore/Qt3DCore>
#include <Qt3DExtras/Qt3DExtras>
#include <Qt3DExtras/QExtrudedTextMesh>

int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);
    Qt3DExtras::Qt3DWindow *view = new Qt3DExtras::Qt3DWindow();

    view->setTitle(QStringLiteral("3D Text CPP"));
    view->setHeight(480);
    view->setWidth(800);
    view->defaultFrameGraph()->setClearColor(QColor("white"));

    auto *root = new Qt3DCore::QEntity();

    Qt3DRender::QCamera *camera = view->camera();
    camera->lens()->setPerspectiveProjection(65.f, 800.0f/480.f, 0.1f, 100.f);
    camera->setPosition(QVector3D(0.f, 1.f, 3.f));
    camera->setViewCenter(QVector3D(0.f, 1.f, 0.f));

    auto *cameraController = new Qt3DExtras::QOrbitCameraController(root);
    cameraController->setCamera(camera);

    QFont font("Mukta Mahee ExtraBold", 32, -1, false);
    auto *textMesh = new Qt3DExtras::QExtrudedTextMesh();
    textMesh->setDepth(.25f);
    textMesh->setFont(font);
    textMesh->setText("TEST");

    auto *textMaterial = new Qt3DExtras::QMetalRoughMaterial(root);
    textMaterial->setBaseColor(QColor("white"));
    textMaterial->setMetalness(1.0);
    textMaterial->setRoughness(0.0);

    auto *textTransform = new Qt3DCore::QTransform();
    textTransform->setTranslation(QVector3D(-2.5f, 1.0f, -0.5f));

    auto *text = new Qt3DCore::QEntity(root);
    text->addComponent(textMaterial);
    text->addComponent(textMesh);
    text->addComponent(textTransform);

    view->setRootEntity(root);
    view->show();

    return a.exec();
}

QML:

import Qt3D.Extras 2.12
import Qt3D.Core 2.12
import Qt3D.Render 2.12
import Qt3D.Input 2.12

Entity {
    id : root

    components: [
           RenderSettings {
               activeFrameGraph: ForwardRenderer {
                   clearColor: "white"
                   camera: camera
               }
           },

            InputSettings { }
    ]

    Camera {
        id: camera

        projectionType: CameraLens.PerspectiveProjection
        fieldOfView: 65
        aspectRatio: 800/480
        nearPlane : 0.1
        farPlane : 100.0

        upVector: Qt.vector3d( 0.0, -1.0, 0.0 ) //<-- y must be -1  to be up?
        position: Qt.vector3d( 0.0, 1.0, 60.0 ) //<--  z was only 3.0 in C++ to get it in the view

        viewCenter: Qt.vector3d( 0.0, 1.0, 0.0 )
    }

    OrbitCameraController {
        camera: camera
    }

    ExtrudedTextMesh {
        id: textMesh
        font.family: "Mukta Mahee ExtraBold"
        font.pixelSize: 32
        font.bold: true
        text: "TEST"
        depth: 0.25
    }

    MetalRoughMaterial {
        id: material
        baseColor: "white"
        metalness: 1.0
        roughness: 0.0
    }

    Transform {
        id: textTransform
        translation: Qt.vector3d(-2.5, 1.0, -0.5)
        scale: 0.8
    }

    Entity {
        id: text3d
        components: [ textMesh, material, textTransform ]
    }
}