如何使用Qt相机进行放大/缩小？

QT += core gui multimedia multimediawidgets

#include <QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QCamera>
#include <QCameraViewfinder>
#include <QCameraImageCapture>
#include <QVBoxLayout>
#include <QPushButton>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void zoomIn();
    void zoomOut();

private:
    QCamera *camera;
    QCameraViewfinder *viewfinder;
    QVBoxLayout *layout;
    QPushButton *zoomInButton;
    QPushButton *zoomOutButton;
    qreal currentZoom;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent), currentZoom(1.0)
{
    camera = new QCamera(this);
    viewfinder = new QCameraViewfinder(this);
    camera->setViewfinder(viewfinder);

    zoomInButton = new QPushButton("Zoom In", this);
    zoomOutButton = new QPushButton("Zoom Out", this);

    layout = new QVBoxLayout();
    layout->addWidget(viewfinder);
    layout->addWidget(zoomInButton);
    layout->addWidget(zoomOutButton);

    QWidget *centralWidget = new QWidget(this);
    centralWidget->setLayout(layout);
    setCentralWidget(centralWidget);

    connect(zoomInButton, &QPushButton::clicked, this, &MainWindow::zoomIn);
    connect(zoomOutButton, &QPushButton::clicked, this, &MainWindow::zoomOut);

    camera->start();
}

MainWindow::~MainWindow()
{
    camera->stop();
}

void MainWindow::zoomIn()
{
    currentZoom += 0.1;
    if (currentZoom > camera->maximumOpticalZoom())
        currentZoom = camera->maximumOpticalZoom();
    camera->focus()->zoomTo(currentZoom, currentZoom);
}

void MainWindow::zoomOut()
{
    currentZoom -= 0.1;
    if (currentZoom < 1.0)
        currentZoom = 1.0;
    camera->focus()->zoomTo(currentZoom, currentZoom);
}