MainWidget::MainWidget(QWidget *parent) : QWidget(parent)
{
    setWindowTitle(QStringLiteral("Basic shapes"));

    QLabel *graphicsLabel = new QLabel();
    graphicsLabel->setGeometry(QRect(0, 0, 400, 400));
    graphicsLabel->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

    QPushButton *genButton = new QPushButton();
    genButton->setText("Generate");
    genButton->setMaximumWidth(100);

    QHBoxLayout *hLayout = new QHBoxLayout(this);
    hLayout->addWidget(graphicsLabel, 1);
    hLayout->addWidget(genButton);

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

    Qt3DRender::QCamera *cameraEntity = new Qt3DRender::QCamera(rootEntity);
    cameraEntity->lens()->setPerspectiveProjection(45.0f, 1.0, 0.1f, 1000.0f);
    cameraEntity->setPosition(QVector3D(0, 20.0, 0));
    cameraEntity->setViewCenter(QVector3D(0, 0, 0));

    // Set up a light to illuminate the shapes.
    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);
    // Plane
    Qt3DExtras::QPlaneMesh *plane = new Qt3DExtras::QPlaneMesh();
    plane->setWidth(2.0);
    plane->setHeight(2.0);

    Qt3DCore::QTransform *planeTr = new Qt3DCore::QTransform();
    planeTr->setScale(5.0);
    planeTr->setRotationX(19);
    planeTr->setRotationY(13);
    planeTr->setRotationZ(10);
    // Material
    Qt3DExtras::QPhongMaterial *mat = new Qt3DExtras::QPhongMaterial();
    mat->setDiffuse(Qt::green);
    // Plane ent
    Qt3DCore::QEntity *planeEnt = new  Qt3DCore::QEntity(rootEntity);
    planeEnt->addComponent(plane);
    planeEnt->addComponent(planeTr);
    planeEnt->addComponent(mat);

    // Create the offscreen engine. This is the object which is responsible for handling the 3D scene itself.
    offscreenEngine = new OffscreenEngine(cameraEntity, QSize(1200, 800));

    // The offscreen engine delegate handles requesting frames from the engine, and drawing their results in the graphics label.
    offscreenEngineDelegate = new OffscreenEngineDelegate(offscreenEngine, graphicsLabel);

    // Set our scene to be rendered by the offscreen engine.
    offscreenEngine->setSceneRoot(rootEntity);
}

OffscreenEngineDelegate::OffscreenEngineDelegate(OffscreenEngine *engine, QLabel *label) :
    engine(engine),
    label(label),
    reply(nullptr)
{
    auto captureDelay = 20;
    QTimer::singleShot(captureDelay, this,[this](){requestRenderCapture();});
}

OffscreenEngineDelegate::~OffscreenEngineDelegate()
{
    delete reply;
}

void OffscreenEngineDelegate::requestRenderCapture()
{
    delete reply;
    reply = engine->getRenderCapture()->requestCapture();
    connect(reply, SIGNAL(completed()), this, SLOT(onImageRendered()));
}

void OffscreenEngineDelegate::onImageRendered()
{
    label->setPixmap(QPixmap::fromImage(reply->image()));
}