QScrollArea 以鼠标位置点放大缩小图片，c 实现

您可以使用QScrollBar结合QGraphicsView来实现该功能。以下是一个简单的实现方法：

#include <QtWidgets>

class ImageViewer : public QGraphicsView {
public:
    ImageViewer(QWidget *parent = nullptr) : QGraphicsView(parent) {
        scene = new QGraphicsScene(this);
        setScene(scene);
        setAlignment(Qt::AlignLeft | Qt::AlignTop);
        setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
        setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
        setRenderHint(QPainter::SmoothPixmapTransform);
        setDragMode(QGraphicsView::ScrollHandDrag);
    }

    void setPixmap(const QPixmap &pixmap) {
        this->pixmap = pixmap;
        scene->clear();
        scene->addPixmap(pixmap);
        fitInView(scene->sceneRect(), Qt::KeepAspectRatio);
        setCursor(Qt::ArrowCursor);
    }

protected:
    void wheelEvent(QWheelEvent *event) override {
        QPoint pos = event->pos();
        QPointF scene_pos = mapToScene(pos);
        qreal factor = qPow(1.001, event->angleDelta().y());
        scale(factor, factor);
        QPointF new_scene_pos = mapToScene(pos);
        QPointF translate = new_scene_pos - scene_pos;
        horizontalScrollBar()->setValue(horizontalScrollBar()->value() + translate.x());
        verticalScrollBar()->setValue(verticalScrollBar()->value() + translate.y());
    }

    void mouseMoveEvent(QMouseEvent *event) override {
        QPoint pos = event->pos();
        QPointF scene_pos = mapToScene(pos);
        if (scene->sceneRect().contains(scene_pos)) {
            qreal factor = 1.05;
            QPixmap copy = pixmap;
            QPainter painter(&copy);
            painter.setRenderHint(QPainter::SmoothPixmapTransform);
            painter.translate(pos);
            painter.scale(factor, factor);
            painter.translate(-pos);
            scene->clear();
            scene->addPixmap(copy);
            setCursor(Qt::OpenHandCursor);
        } else {
            scene->clear();
            scene->addPixmap(pixmap);
            setCursor(Qt::ArrowCursor);
        }
    }

    void leaveEvent(QEvent *event) override {
        scene->clear();
        scene->addPixmap(pixmap);
        setCursor(Qt::ArrowCursor);
    }

private:
    QGraphicsScene *scene;
    QPixmap pixmap;
};

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

    QWidget *widget = new QWidget;
    QVBoxLayout *layout = new QVBoxLayout(widget);
    ImageViewer *viewer = new ImageViewer(widget);
    layout->addWidget(viewer);

    QPixmap pixmap(":/image.jpg");
    viewer->setPixmap(pixmap);

    widget->show();
    return app.exec();
}

在这个实现中，我们使用QGraphicsView来显示图片，并通过QScrollBar来实现放大和缩小。在鼠标移动事件中，我们将鼠标位置作为放大的中心点，并在场景中绘制一个缩放后的副本。在鼠标离开事件中，我们恢复原始的图片。同时，我们在滚轮事件中实现了按鼠标位置放大和缩小的功能。