1. 例程代码

void Widget::paintEvent(QPaintEvent *event)
{
    
    QPainter painter;
    
    //绘制image
    QImage image(100,100,QImage::Format_ARGB32);
    painter.begin(&image);
    painter.setPen(QPen(Qt::red,3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10,10,60,60);
    painter.drawText(10,10,60,60,Qt::AlignCenter,tr("QImage"));
    painter.setBrush(QColor(0,0,0,100));
    painter.drawRect(50,50,40,40);
    painter.end();
    
    //绘制pixmap
    QPixmap pix(100,100);
    painter.begin(&pix);
    painter.setPen(QPen(Qt::red,3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10,10,60,60);
    painter.drawText(10,10,60,60,Qt::AlignCenter,tr("QPixmap"));
    painter.setBrush(QColor(0,0,0,100));
    painter.drawRect(50,50,40,40);
    painter.end();

    //绘制bitmap
    QBitmap bit(100,100);
    painter.begin(&bit);
    painter.setPen(QPen(Qt::red,3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10,10,60,60);
    painter.drawText(10,10,60,60,Qt::AlignCenter,tr("QBitmap"));
    painter.setBrush(QColor(0,0,0,100));
    painter.drawRect(50,50,40,40);
    painter.end();

    //绘制picture
    QPicture picture;
    painter.begin(&picture);
    painter.setPen(QPen(Qt::red,3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10,10,60,60);
    painter.drawText(10,10,60,60,Qt::AlignCenter,tr("QPicture"));
    painter.setBrush(QColor(0,0,0,100));
    painter.drawRect(50,50,40,40);
    painter.end();

    //在widget部件上进行绘制
    painter.begin(this);
    painter.drawImage(50,20,image);
    painter.drawPixmap(200,20,pix);
    painter.drawPixmap(50,170,bit);
    painter.drawPicture(200,170,picture);
}

2. 四个常用的绘图设备

2.1 QImage

• QImage主要用来进行I/O处理，它对I/O处理操作进行了优化，而且可以用来直接访问和操作像素；

2.2 QPixmap

• QPixmap主要用来在屏幕上显示图像，它对在屏幕上显示图像那个进行了优化；

2.3 QBitmap

• QBitmap 是 QPixmap 的子类，用来处理颜色深度为1的图像，即只能显示黑白两种颜色；

2.4 QPicture

• QPicture用来记录并重演QPainter命令。

3. 复合模式

void Widget::paintEvent(QPaintEvent *event)
{
    
    QPainter painter;
    QImage image(400,300,QImage::Format_ARGB32_Premultiplied);
    painter.begin(&image);
    painter.setBrush(Qt::green);
    painter.drawRect(100,50,200,200);
    painter.setBrush(QColor(0,0,255,15));
    painter.drawRect(50,0,100,100);
    painter.setCompositionMode(QPainter::CompositionMode_SourceIn);
    painter.drawRect(250,0,100,100);
    painter.setCompositionMode(QPainter::CompositionMode_DestinationOver);
    painter.drawRect(50,200,100,100);
    painter.setCompositionMode(QPainter::CompositionMode_Xor);
    painter.drawRect(250,200,100,100);
    painter.end();
    painter.begin(this);
    painter.drawImage(0,0,image);
}