用qt写一个可以在图片上任意画有限条线，且在各条线起点和终点旁边分别显示像素坐标的代码，坐标的原点为图像的左上角，头文件和源文件分开

### 回答1：
头文件：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QImage>
#include <QPainter>
#include <QMouseEvent>

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    QImage image;
    QPainter painter;
    QPoint startPt, endPt;
    QList<QLine> lines;

protected:
    void paintEvent(QPaintEvent *event);
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
};

#endif // MAINWINDOW_H

源文件：

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    image = QImage(640, 480, QImage::Format_RGB32);
    image.fill(Qt::white);
}

MainWindow::~MainWindow()
{
}

void MainWindow::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    painter.begin(this);
    painter.drawImage(0, 0, image);
    painter.end();
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    startPt = event->pos();
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
    endPt = event->pos();
    update();
}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
    endPt = event->pos();
    lines << QLine(startPt, endPt);
    update();
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    image = QImage(640, 480, QImage::Format_RGB32);
    image.fill(Qt::white);
}

MainWindow::~MainWindow()
{
}

void MainWindow::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    painter.begin(&image);
    painter.setPen(Qt::black);
    for (const QLine &line : lines) {
        painter.drawLine(line);
        painter.drawText(line.p1() + QPoint(5, -5), QString("(%1, %2)").arg(line.x1()).arg(line.y1()));
        painter.drawText(line.p2() + QPoint(5, -5), QString("(%1, %2)").arg(line.x2()).arg(line.y2()));
    }
    painter.setPen(Qt::red);
    painter.drawLine(startPt, endPt);
    painter.drawText(startPt + QPoint(5, -5), QString("(%1, %2)").arg(startPt.x()).arg(startPt.y()));
    painter.drawText(endPt + QPoint(5, -5), QString("(%1, %2)").arg(endPt.x()).arg(endPt.y()));
    painter.end();
    QMainWindow::paintEvent(event);
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    startPt = event->pos();
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
    endPt = event->pos();
    update();
}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
    endPt = event->pos();
    lines << QLine(startPt, endPt);
    update();
}

### 回答2：
头文件（linepainter.h）：

#ifndef LINEPAINTER_H
#define LINEPAINTER_H

#include <QWidget>
#include <QPoint>
#include <QVector>

class LinePainter : public QWidget
{
Q_OBJECT

public:
explicit LinePainter(QWidget *parent = nullptr);
void addLine(const QPoint &start, const QPoint &end);

protected:
void paintEvent(QPaintEvent *event) override;

private:
QVector<QPair<QPoint, QPoint>> m_lines;
};

#endif // LINEPAINTER_H

源文件（linepainter.cpp）：

#include "linepainter.h"
#include <QPainter>

LinePainter::LinePainter(QWidget *parent)
: QWidget(parent)
{
}

void LinePainter::addLine(const QPoint &start, const QPoint &end)
{
m_lines.append(qMakePair(start, end));
update(); // 更新绘制
}

void LinePainter::paintEvent(QPaintEvent *event)
{
QWidget::paintEvent(event);

QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing); // 抗锯齿

// 绘制所有线条
for (const auto &line : m_lines) {
painter.drawLine(line.first, line.second);
}

// 绘制线条起点和终点的像素坐标
QFont font;
font.setPixelSize(12);
painter.setFont(font);
painter.setPen(Qt::red);
for (const auto &line : m_lines) {
painter.drawText(line.first, QString("(%1,%2)").arg(line.first.x()).arg(line.first.y()));
painter.drawText(line.second, QString("(%1,%2)").arg(line.second.x()).arg(line.second.y()));
}
}

使用方法示例：

#include "linepainter.h"
#include <QtWidgets>

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

QWidget window;
QVBoxLayout layout(&window);
LinePainter painter;
layout.addWidget(&painter);
window.setLayout(&layout);
window.show();

// 添加线条
painter.addLine(QPoint(50, 100), QPoint(200, 150));
painter.addLine(QPoint(100, 200), QPoint(300, 250));

return a.exec();
}

运行上述示例代码，可以在窗口上绘制两条线，并在每条线的起点和终点旁边显示像素坐标。

### 回答3：
头文件（imagepainter.h）：

#ifndef IMAGE_PAINTER_H
#define IMAGE_PAINTER_H

#include <QImage>
#include <QPainter>
#include <QWidget>
#include <QMouseEvent>

class ImagePainter : public QWidget
{
    Q_OBJECT

public:
    explicit ImagePainter(QWidget *parent = nullptr);
    void setImage(const QImage &image);

protected:
    void paintEvent(QPaintEvent *event) override;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;

private:
    QImage m_image;
    QVector<QLine> m_lines;
    QPoint m_startPoint;
};

#endif // IMAGE_PAINTER_H

源文件（imagepainter.cpp）：

#include "imagepainter.h"

ImagePainter::ImagePainter(QWidget *parent) : QWidget(parent)
{

}

void ImagePainter::setImage(const QImage &image)
{
    m_image = image;
    update();
}

void ImagePainter::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.drawImage(0, 0, m_image);

    painter.setPen(Qt::red);
    for (const QLine &line : m_lines) {
        painter.drawLine(line);
    }
}

void ImagePainter::mousePressEvent(QMouseEvent *event)
{
    m_startPoint = event->pos();
    event->accept();
}

void ImagePainter::mouseReleaseEvent(QMouseEvent *event)
{
    QPoint endPoint = event->pos();
    QLine line(m_startPoint, endPoint);
    m_lines.append(line);
    event->accept();
    update();
}

使用示例（main.cpp）：

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

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

    QImage image(":/images/example.jpg");

    ImagePainter painter;
    painter.setImage(image);
    painter.show();

    return a.exec();
}

上述代码定义了一个名为ImagePainter的自定义QWidget，并在其上实现了图片绘制功能。通过mousePressEvent和mouseReleaseEvent函数，可以在图片上绘制任意数量的线条。每绘制一条线条后，会在该线条的起点和终点旁边显示像素坐标。坐标的原点为图像的左上角。在使用时，只需将所需绘制的图片路径传递给setImage函数即可。