初識Qt塗鴉板繪製

一、新建一個Qt Gui應用，項目名稱爲myPalette，基類選擇爲QMainWindow，類名設置爲MainWindow。

二、在mainwindow.h頭文件中添加如下代碼，同時添加#include<QPushButton>

 1 private:
 2     Ui::MainWindow *ui;
 3     QPixmap pix;
 4     QPoint lastPoint;
 5     QPoint endPoint;
 6     qreal scale;
 7     QPushButton *zoomInButton, *zoomOutButton;
 8 
 9 protected:
10     void paintEvent(QPaintEvent *);
11     void mousePressEvent(QMouseEvent *);
12     void mouseMoveEvent(QMouseEvent *);
13     void mouseReleaseEvent(QMouseEvent *);
14 
15 public slots:
16     void zoomIn();
17     void zoomOut();

三、在mainwindow.cpp文件中添加#include<QPainter>，同時在構造函數中添加如下代碼段

 1  resize(600, 500);//窗口大小
 2     pix = QPixmap(400, 400);//畫布大小
 3     pix.fill(Qt::white);
 4 
 5     scale = 1;//不放大
 6     zoomInButton = new QPushButton(this);//放大按鈕
 7     zoomInButton->setText(tr("zoomIn"));
 8     zoomInButton->move(400,450);
 9     zoomOutButton = new QPushButton(this);//縮小按鈕
10     zoomOutButton->setText(tr("zoomOut"));
11     zoomOutButton->move(500,450);
12 
13     connect(zoomInButton, SIGNAL(clicked()), this, SLOT(zoomIn()));
14     connect(zoomOutButton, SIGNAL(clicked()), this, SLOT(zoomOut()));

四、在mainwindow.cpp文件中配置相關的事件函數，代碼以下

 1 void MainWindow::paintEvent(QPaintEvent *)
 2 {
 3     QPainter pp(&pix);
 4     pp.drawLine(lastPoint/scale, endPoint/scale);//保證畫布座標和窗口座標相同，避免窗口座標變化，而畫布座標未發生改變
 5     lastPoint = endPoint;
 6     QPainter painter(this);
 7     painter.scale(scale, scale);//進行放大操做，放大的是窗口座標。若是想放大畫布座標，則執行pp.scale(scale, scale);
 8     painter.drawPixmap(0, 0, pix);//從窗口的原點（0, 0）添加該QPixmap對象，在窗口中放置畫布pix。
 9                                                   //若drawPixmap(0, 0, 100, 100, pix)，則指定了添加對象的尺寸大小
10 }
11 
12 void MainWindow::mousePressEvent(QMouseEvent *event)
13 {
14     if(event->button() == Qt::LeftButton)//button()函數返回的是按下的鍵，直接判斷是否爲某個鍵。適用於鼠標鍵一次按下
15     {
16         lastPoint = event->pos();
17     }
18 }
19 
20 void MainWindow::mouseMoveEvent(QMouseEvent *event)
21 {
22     if(event->buttons()&Qt::LeftButton)//buttons()函數返回的是按下的鍵的狀態，須要經過OR運算進行判斷。適用於鼠標鍵持續按下
23     {
24         endPoint = event->pos();
25         update();//調用update()函數會進行paintEvent()函數的從新繪製
26     }
27 }
28 
29 void MainWindow::mouseReleaseEvent(QMouseEvent *event)
30 {
31     if(event->button() == Qt::LeftButton)
32     {
33         endPoint = event->pos();
34         update();
35     }
36 }
37 
38 void MainWindow::zoomIn()
39 {
40     scale *= 2;//放大兩倍
41     update();
42 }
43 
44 void MainWindow::zoomOut()
45 {
46     scale /= 2;//縮小兩倍
47     update();
48 }

五、運行結果以下