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 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51

#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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135

#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(100, 100), tux);

    drawing = false;
    brushColor = Qt::black;
    brushSize = 2;

}

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(255, 255, 255));
    QPainter painter(&newImage);
    painter.drawImage(QPoint(0, 0), image);
    image = newImage;

}

void MainWindow::on_action_2px_triggered()
{
    brushSize = 2;
}

void MainWindow::on_action_5px_triggered()
{
    brushSize = 5;
}

void MainWindow::on_action_10px_triggered()
{
    brushSize = 10;
}

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14

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

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

    MainWindow w;
    w.resize(640, 480);
    w.show();

    return a.exec();
}

编译运行，自由绘制吧！