30.QT-渐变之QLinearGradient、 QConicalGradient、QRadialGradient

void QGradient::setSpread ( Spread method );
//设置填充梯度区域外的区域,参数有:
// QGradient::PadSpread  ：填充区域内最接近的停止颜色。这是默认的。
// QGradient::RepeatSpread : 在区域外继续重复填充
// QGradient::ReflectSpread : 在区域外反射填充

QGradient::setCoordinateMode ( CoordinateMode mode );
//设置渐变的坐标模式,比如QGradient::LogicalMode设置坐标为逻辑坐标(默认为该值)

void setColorAt ( qreal position, const QColor & color );
                     //设置梯度颜色, position处于0~1之间

QLinearGradient ( qreal x1, qreal y1, qreal x2, qreal y2 )
//其中x1,y1表示渐变起始坐标, x2,y2表示渐变终点坐标
//如果只有x相等,则表示垂直线性渐变,如果只有y相等,则表示平行线性渐变,否则就是斜角线性渐变

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    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
}

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing,true);
    QLinearGradient Linear(100,100,200,100);        //水平渐变

    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
}

QRadialGradient ( qreal cx, qreal cy, qreal radius, qreal fx, qreal fy );
// cx cy : 设置圆的中心原点(center)
// radius:设置圆半径
//fx fy : 设置焦点focus,也就是颜色的起始位置

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.translate(width()/2,height()/2);
    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);
}

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.translate(width()/2,height()/2);
    QRadialGradient Radial(0,0,120,0,60);    //设置焦点在(0,60),半径120

    Radial.setColorAt(0,Qt::red);
    Radial.setColorAt(0.5,Qt::blue);
    Radial.setColorAt(1,Qt::green);

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

QConicalGradient ( qreal cx, qreal cy, qreal angle );
//设置(cx,cy)位置为圆锥尖,设置angle角度为起始颜色位置(顺时针渐变)

void Widget::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing,true);
    painter.translate(width()/2,height()/2);

    QConicalGradient Conical(0,0,30);    //设置点在中心,角度为30
    Conical.setColorAt(0,Qt::red);
    Conical.setColorAt(0.5,Qt::blue);
    Conical.setColorAt(1,Qt::green);

    painter.setPen(Qt::transparent);
    painter.setBrush(Conical);
    painter.drawEllipse(-120,-120,240,240);
}