类QPainter的常用语句：
void PainterTest::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    /*QPen pen; //画笔
    pen.setColor(QColor(255,0,0));
    QBrush brush(QColor(0,255,0,125)); //画刷
    */
    QPen pen(Qt::DotLine);
    QBrush brush(Qt::blue);
    brush.setStyle(Qt::HorPattern);

    painter.setPen(pen); //添加画笔
    painter.setBrush(brush); //添加画刷

    /*画弧形*/
    QRectF rectangle(10.0, 20.0, 80.0, 60.0); //矩形
    int startAngle = 30 * 16;     //起始角度
    int spanAngle = 120 * 16;   //跨越度数
    /*设置渐变*/
    QLinearGradient linearGradient(100,150,300,150);
       //从点（100，150）开始到点（300，150）结束，确定一条直线
    linearGradient.setColorAt(0,Qt::red);
    linearGradient.setColorAt(0.2,Qt::black);
    linearGradient.setColorAt(0.4,Qt::yellow);
    linearGradient.setColorAt(0.6,Qt::white);
    linearGradient.setColorAt(0.8,Qt::green);
    linearGradient.setColorAt(1,Qt::blue);//将直线开始点设为0，终点设为1，然后分段设置颜色
    painter.setBrush(linearGradient);

    /*圆锥渐变*/
    // QConicalGradient conicalGradient(50,50,0);//圆心为（50，50），开始角度为0
    // conicalGradient.setColorAt(0,Qt::green);
    //conicalGradient.setColorAt(1,Qt::white); //从圆心的0度角开始逆时针填充
    //painter.setBrush(conicalGradient);
    /*矩形框中画字体*/
    QRectF ff(10,10,30,40); //设置一个矩形
    painter.drawRect(ff);    //为了更直观地看到字体的位置，我们绘制出这个矩形
    painter.setPen(QColor(Qt::blue));//设置画笔颜色为红色
    painter.drawText(ff,Qt::AlignHCenter,"World");

    /*设置字体*/
    QFont font("Arial",20,QFont::Bold,true);
        //设置字体的类型，大小，加粗，斜体
        font.setUnderline(true);
        //设置下划线
        font.setOverline(true);
        //设置上划线
        font.setCapitalization(QFont::SmallCaps);
        //设置大小写
        font.setLetterSpacing(QFont::AbsoluteSpacing,5);
        //设置间距

    painter.setFont(font);
    painter.drawLine(0,0,100,100);//画直线
    painter.drawArc(rectangle, startAngle, spanAngle);//画弧线
    painter.drawRect(100,100,200,100);//又画了个矩形
    painter.drawEllipse(100,0,200,200);//画圆


}


QpinterPath类常用函数：


void PainterTest::paintEvent(QPaintEvent *)
{
    QPainterPath path;
    path.lineTo(100,100);
    path.lineTo(200,100);
    path.addEllipse(100,100,50,50);
    path.lineTo(200,200);

    QPainter painter(this);
    painter.setPen(Qt::green);
    painter.setBrush(Qt::yellow);

    painter.drawPath(path);
    QPainterPath path2;
    path2.addPath(path);
    path2.translate(100,0);

    path2.moveTo(100,100);//可见moveTo函数可以改变当前点的位置
    path2.lineTo(300,300);

    painter.drawPath(path2);



}
void PainterTest::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
       QPixmap pix;
       pix.load("images/4.ico");
       painter.drawPixmap(0,0,100,100,pix);
       
       painter.translate(50,50); //让图片的中心作为旋转的中心
          painter.rotate(90); //顺时针旋转90度
          
       qreal width = pix.width(); //获得以前图片的宽和高
       qreal height = pix.height();
       
       pix = pix.scaled(width*2,height*2,Qt::KeepAspectRatio);
           //将图片的宽和高都扩大两倍，并且在给定的矩形内保持宽高的比值
       painter.drawPixmap(100,100,pix);


}