30.QT

渐变有三种：QLinearGradient、QConicalGradient 、 QRadialGradient

它们都有一个QGradient父类

QGradient父类的常用公共函数有：

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线性渐变

构造函数函数如下:

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

示例1-垂直渐变:

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}

 

示例2-水平渐变

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半径渐变

更据圆的半径来设定不同的颜色

构造函数函数如下:

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

示例1:

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);}

 

示例2:

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圆锥渐变

构造函数如下所示:

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(逆时针渐变)

示例:

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);}

 

未完,下章来学习: 

31.QPainter-rotate()函数分析-文字旋转不倾斜,图片旋转实现等待