Qt 渐变色Gradient

线性渐变 QLinearGradient
弧度渐变 QConicalGradient
辐射渐变 QRadialGradient

    QPainter painter(this);
    //线性渐变
    QLinearGradient linearGradient(0,0,150,150);
    linearGradient.setColorAt(0.2,Qt::white);
    linearGradient.setColorAt(0.6,Qt::blue);
    linearGradient.setColorAt(1.0,Qt::yellow);
    painter.setBrush(QBrush(linearGradient));
    painter.drawEllipse(0,0,200,150);
    //保存当前的painter 放到堆中 save()函数必须有对应的restore()函数
    //restore()函数 恢复painter的状态(从堆中取出来)
    painter.save();

    painter.translate(200,0);   //以原坐标的(200,0)为新的坐标系坐标原点(0,0)
    const int r = 100;
    painter.setRenderHint(QPainter::Antialiasing,true);
    //弧度渐变
    //弧度渐变由圆心(xc,yc)和一个角度a定义。颜色从圆心开始像表的秒针一样扩散。
    //QConicalGradient(qreal cx, qreal cy, qreal angle)  圆心在坐标原点(0,0)角度从60度开始
    QConicalGradient conicalGradient(0,0,60);
    conicalGradient.setColorAt(0.0,Qt::red);
//    conicalGradient.setColorAt(60.0/360.0,Qt::yellow);
//    conicalGradient.setColorAt(120.0/360.0,Qt::green);
//    conicalGradient.setColorAt(180.0/360.0,Qt::cyan);
//    conicalGradient.setColorAt(240.0/360.0,Qt::blue);
//    conicalGradient.setColorAt(300.0/360.0,Qt::magenta);
    conicalGradient.setColorAt(1.0,Qt::yellow);

    //translate(r,r)  以原坐标的(r,r)为新的坐标系坐标原点(0,0)cx,cy  即相对于窗口(300,100)
    painter.translate(r,r);
    //QBrush brush(brush Style);
    QBrush brush(conicalGradient);
    painter.setPen(Qt::NoPen);
    painter.setBrush(brush);
    painter.drawEllipse(QPoint(0,0),r,r);
    painter.save();

//辐射渐变
    //圆心(0,0)cx,cy 角度0 radius 焦点(30,30)fx,fy开始向外扩散
    painter.translate(0,200);
    QRadialGradient radialGradient(0,0,100,50,50);
    radialGradient.setColorAt(0,Qt::green);
    radialGradient.setColorAt(0.8,Qt::red);
    painter.translate(r,r);
    painter.setBrush(QBrush(radialGradient));
    painter.drawEllipse(QPoint(0,0),r,r);
    painter.save();

    //辐射渐变
    //QRadialGradient radialGradient(310,110,100,330,130);
    ////创建了一个QRadialGradient对象实例，参数分别为中心坐标，半径长度和焦点坐标,如果需要对称那么中心坐标和焦点坐标要一致
    //radialGradient.setColorAt(0,Qt::green);
    ////radialGradient.setColorAt(0.2,Qt::white);
    //radialGradient.setColorAt(0.4,Qt::blue);
    ////radialGradient.setColorAt(0.6,Qt::red);
    //radialGradient.setColorAt(1.0,Qt::yellow);
    //painter.setBrush(QBrush(radialGradient));
    //painter.drawEllipse(210,10,200,200);//在相应的坐标画出来
    painter.restore();