【Essence】Realize the magnifying glass function in Qt

To implement the Magnifier feature in Qt, you can create a custom Magnifier control and utilize mouse events and drawings to achieve the Magnifier effect.

Here is a simple sample code that demonstrates how to implement the Magnifier feature in Qt:

#include <QApplication>
#include <QMouseEvent>
#include <QPainter>
#include <QPixmap>
#include <QWidget>

class MagnifierWidget : public QWidget {
    Q_OBJECT

public:
    explicit MagnifierWidget(QWidget* parent = nullptr)
        : QWidget(parent),
          zoomFactor(2.0),
          radius(100),
          pixmap(nullptr) {
        setFixedSize(radius * 2, radius * 2);
        setMouseTracking(true);
    }

    void setZoomFactor(double factor) {
        zoomFactor = factor;
        update();
    }

    void setRadius(int r) {
        radius = r;
        setFixedSize(radius * 2, radius * 2);
        update();
    }

protected:
    void mouseMoveEvent(QMouseEvent* event) override {
        if (pixmap) {
            int x = event->pos().x() - radius;
            int y = event->pos().y() - radius;

            QPoint sourcePoint(x / zoomFactor, y / zoomFactor);
            QRect sourceRect(sourcePoint.x(), sourcePoint.y(), width() / zoomFactor, height() / zoomFactor);
            QPixmap zoomedPixmap = pixmap->copy(sourceRect);

            QPainter painter(this);
            painter.setRenderHint(QPainter::SmoothPixmapTransform, true);
            painter.drawPixmap(rect(), zoomedPixmap);
        }
    }

    void paintEvent(QPaintEvent* event) override {
        Q_UNUSED(event);

        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing);

        if (pixmap) {
            painter.drawPixmap(rect(), *pixmap);
        } else {
            painter.fillRect(rect(), Qt::white);
        }

        // 绘制放大镜边框
        painter.setPen(Qt::black);
        painter.setBrush(Qt::NoBrush);
        painter.drawEllipse(rect().adjusted(0, 0, -1, -1));
    }

public slots:
    void setPixmap(const QPixmap& pixmap) {
        this->pixmap = new QPixmap(pixmap);
        update();
    }

private:
    double zoomFactor;    // 缩放因子
    int radius;           // 放大镜半径
    QPixmap* pixmap;      // 原始图片的指针
};

           

Usage examples:

#include <QApplication>
#include <QLabel>
#include <QPixmap>
#include <QVBoxLayout>
#include "magnifierwidget.h"

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

    QLabel* imageLabel = new QLabel;
    QPixmap pixmap(":/path/to/your/image.jpg");
    imageLabel->setPixmap(pixmap);

    MagnifierWidget* magnifier = new MagnifierWidget;
    magnifier->setPixmap(pixmap);
    magnifier->setZoomFactor(2.5); // 设置放大因子，默认为2.0
    magnifier->setRadius(100);     // 设置放大镜半径，默认为100

    QVBoxLayout* layout = new QVBoxLayout;
    layout->addWidget(imageLabel);
    layout->addWidget(magnifier);

    QWidget window;
    window.setLayout(layout);
    window.show();

    return a.exec();
}
           

In the above code, you need to replace :/path/to/your/image.jpg with your own image path. You can then adapt to your needs by adjusting the zoom factor and radius of the magnifier. Finally, place the MagnifierWidget above the image to achieve the function of Magnifier.

Note: In order to use the above code, you need to create a header file named "magnifierwidget.h" and add #include <QWidget> and #include to it<QPixmap>.