Qt之渐变QLinearGradient、QRadialGradient、QConicalGradient

1、QLinearGradient

线性渐变代码一及演示：

void MainWindow::drawLine(QPainter *painter)
{
    painter->save();

    painter->setRenderHint(QPainter::Antialiasing,true);
    QLinearGradient Linear(100,100,100,200);        //垂直渐变
    
    Linear.setColorAt(0,Qt::red);
    Linear.setColorAt(1,Qt::blue);
    
    painter->setBrush(Linear);
    painter->setPen(Qt::transparent);
    painter->drawRect(100,100,100,100);          //100,100 到200,200
    painter->restore();
}

 线性渐变代码二及演示：

void MainWindow::drawTriangle(QPainter *painter)
{
    painter->save();
    double radius =100;
    painter->setPen(Qt::NoPen);
    static const QPointF points[3]={QPointF(radius,0),QPointF(0,0),QPointF(radius/2,sqrt(pow(radius,2)-pow(radius/2,2)))};
    QLinearGradient linear(0,0,radius,0);
    linear.setColorAt(0,Qt::red);
    linear.setColorAt(1,Qt::blue);
    painter->setBrush(linear);
//    painter->setBrush(Qt::red);
    painter->drawConvexPolygon(points,3);
    painter->restore();
}

 

2、QRadialGradient

QRadialGradient(qreal cx, qreal cy, qreal radius, qreal fx, qreal fy);

cx,cy:圆的中心位置

fx,fy:焦点的位置

radius：圆的半径

//半径渐变
void MainWindow::drawRadial(QPainter *painter)
{
    painter->save();
    QRadialGradient Radial(0,0,120,0,0);    //设置圆的原点和焦点在中心,半径120

    Radial.setColorAt(0,Qt::red);
    Radial.setColorAt(0.5,Qt::blue);        //设置50%处的半径为蓝色
    Radial.setColorAt(1,Qt::green);

    painter->setPen(Qt::transparent);
    painter->setBrush(Radial);
    painter->drawEllipse(-120,-120,240,240);
    painter->restore();
}

 

3、QConicalGradient圆锥渐变

conical.setColorAt(qreal pos, QColor color);

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pos在drawPie时表示的意思是从起始角度开始，起始角度占比为0。占完整(0,360)的比例值。

color在drawPie时表示的意思是当前所占比例处的颜色。

QConicalGradient(qreal cx, qreal cy, qreal angle)

cx，cy：表示中心位置

angle:表示起始角度

绘制饼图是按照pos是按照360的比例

圆锥渐变代码一及演示图片：

void MainWindow::drawPie(QPainter *painter)
{
    painter->save();
    painter->setPen(Qt::NoPen);

    //设置(cx,cy)位置为圆锥尖,设置angle角度为起始颜色位置(逆时针渐变)
    QConicalGradient Conical(0,0,00);    //设置点在中心,角度为30
    Conical.setColorAt(0,Qt::red);
    Conical.setColorAt(0.25,Qt::blue);
    Conical.setColorAt(1,Qt::green);     //pos表示占完整pie(0,360)的一个比例值

    painter->setPen(Qt::transparent);
    painter->setBrush(Conical);
    painter->drawPie(-120,-120,240,240,0*16,90*16);
//    painter->drawEllipse(-120,-120,240,240);
    painter->restore();
}

代码及图片演示二：

 

代码及图片演示三：

 

代码及图片演示四