QT制作一个位图画图板程序

本文学习如何创建一个Qt绘制程序，用户将能够通过使用不同的尺寸和画笔的颜色来表达他们的创造力。

主要功能：保存画板内容为图片、清除画板内容、设置画板大小、设置画笔颜色

新建基于QMainWindow的应用程序，设置MainWindow.ui

代码如下:

MainWindow.h

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#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

#include <QPainter>
#include <QMouseEvent>
#include <QFileDialog>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

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

virtual void mousePressEvent(QMouseEvent *event);
    virtual void mouseMoveEvent(QMouseEvent *event);
    virtual void mouseReleaseEvent(QMouseEvent *event);
    virtual void paintEvent(QPaintEvent *event);
    virtual void resizeEvent(QResizeEvent *event);

private slots:
    void on_action_2px_triggered();
    void on_action_5px_triggered();
    void on_action_10px_triggered();
    void on_action_Black_triggered();
    void on_action_White_triggered();
    void on_action_Red_triggered();
    void on_action_Green_triggered();
    void on_action_Blue_triggered();
    void on_action_Save_triggered();
    void on_action_Clear_triggered();

private:
    Ui::MainWindow *ui;
    QImage          image;
    bool            drawing;
    QPoint          lastPoint;
    int             brushSize;
    QColor          brushColor;
};

#endif // MAINWINDOW_H

MainWindow.cpp

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#include “MainWindow.h”
#include “ui_MainWindow.h”
#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

//  create a QImage object, which acts as the canvas
    image = QImage(this->size(), QImage::Format_RGB32);
    image.fill(Qt::white);

QImage tux;
    //tux.load(qApp->applicationDirPath() + “/tux.png”);
    tux.load(“://tux.png”);
    QPainter painter(&image);
    painter.drawImage(QPoint(), tux);

drawing = false;
brushColor = Qt::black;
brushSize = ;

}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        drawing = true;
        lastPoint = event->pos();
    }

}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
    if ((event->buttons() & Qt::LeftButton) && drawing)
    {
        QPainter painter(&image);
        painter.setPen(QPen(brushColor, brushSize, Qt::SolidLine,
                            Qt::RoundCap, Qt::RoundJoin));
        painter.drawLine(lastPoint, event->pos());
        lastPoint = event->pos();
        this->update();
    }

}

void MainWindow::mouseReleaseEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        drawing = false;
    }

}

void MainWindow::paintEvent(QPaintEvent *event)
{
QPainter canvasPainter(this);
canvasPainter.drawImage(this->rect(), image, image.rect());
}

void MainWindow::resizeEvent(QResizeEvent *event)
{
    QImage newImage(event->size(), QImage::Format_RGB32);
    newImage.fill(qRgb());
    QPainter painter(&newImage);
    painter.drawImage(QPoint(), image);
    image = newImage;

}

void MainWindow::on_action_2px_triggered()
{
brushSize = ;
}

void MainWindow::on_action_5px_triggered()
{
brushSize = ;
}

void MainWindow::on_action_10px_triggered()
{
brushSize = ;
}

void MainWindow::on_action_Black_triggered()
{
brushColor = Qt::black;
}

void MainWindow::on_action_White_triggered()
{
brushColor = Qt::white;
}

void MainWindow::on_action_Red_triggered()
{
brushColor = Qt::red;
}

void MainWindow::on_action_Green_triggered()
{
brushColor = Qt::green;
}

void MainWindow::on_action_Blue_triggered()
{
brushColor = Qt::blue;
}

void MainWindow::on_action_Save_triggered()
{
    QString filePath = QFileDialog::getSaveFileName(this, “Save Image”,
                                                    “”, “PNG (*.png);;JPEG (*.jpg *.jpeg);;All files (*.*)”);
    if (filePath == “”)
        return;
    image.save(filePath);
}

void MainWindow::on_action_Clear_triggered()
{
image.fill(Qt::white);
this->update();
}

main.cpp

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#include “MainWindow.h”
#include <QApplication>

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

MainWindow w;
w.resize();
w.show();

return a.exec();
}

编译运行，自由绘制吧！

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