Qt版本：Qt6

具体代码：

1. 头文件 dialog.h

#ifndef DIALOG_H
#define DIALOG_H#include <QDialog>QT_BEGIN_NAMESPACE
namespace Ui {
class Dialog;
}
QT_END_NAMESPACEclass Dialog : public QDialog
{Q_OBJECTpublic:Dialog(QWidget *parent = nullptr);~Dialog();private:Ui::Dialog *ui;
private:QPixmap pix;QPoint lastPoint;//记录鼠标位置QPoint endPoint;//记录鼠标位置
protected:void paintEvent(QPaintEvent *);void mousePressEvent(QMouseEvent *);void mouseMoveEvent(QMouseEvent *);void mouseReleaseEvent(QMouseEvent *);
};
#endif // DIALOG_H

2. 源文件 dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
#include <QPixmap>
#include <QPoint>
#include <QPainter>
#include <QMouseEvent>
Dialog::Dialog(QWidget *parent): QDialog(parent), ui(new Ui::Dialog)
{ui->setupUi(this);//设置窗口大小resize(600, 500);//设置画布大小和背景pix = QPixmap(200, 200);pix.fill(Qt::white);
}Dialog::~Dialog()
{delete ui;
}
void Dialog::paintEvent(QPaintEvent *e)
{QPainter painter(this);painter.drawPixmap(0, 0, pix); // 将绘制的图像绘制到窗口上
}void Dialog::mousePressEvent(QMouseEvent *e)
{if (e->button() == Qt::LeftButton)//==:鼠标事件的掩码信息与LeftButton标记信息相等即表示鼠标坐点击{lastPoint = e->pos(); // 记录鼠标点击的起始点}
}void Dialog::mouseMoveEvent(QMouseEvent *e)
{if (e->buttons() & Qt::LeftButton)//&:鼠标事件的掩码信息中包含有LeftButton标记信息即表示鼠标在移动{QPainter painter(&pix); // 创建一个QPainter对象，并将其绑定到pix上painter.setPen(QPen(Qt::black, 3)); // 设置画笔颜色和线宽painter.drawLine(lastPoint, e->pos()); // 在pixmap上绘制线条lastPoint = e->pos(); // 更新lastPoint为当前鼠标位置update(); // 触发窗口的重绘--更新画板}
}void Dialog::mouseReleaseEvent(QMouseEvent *e)
{if (e->button() == Qt::LeftButton){QPainter painter(&pix); // 创建一个QPainter对象，并将其绑定到pix上painter.setPen(QPen(Qt::black, 3)); // 设置画笔颜色和线宽painter.drawLine(lastPoint, e->pos()); // 在pixmap上绘制线条update(); // 触发窗口的重绘--更新画板}
}

3. 源文件 main.cpp

#include "dialog.h"#include <QApplication>int main(int argc, char *argv[])
{QApplication a(argc, argv);Dialog w;w.show();return a.exec();
}