QBrush之路径渐变画刷(CoordinateMode::LogicalMode与CoordinateMode::ObjectMode)

1、Qt中路径渐变画刷默认的坐标系为CoordinateMode::LogicalMode，该模式下，路径渐变遵循既定规则按整个窗体的坐标系进行渐变填充，以下代码及图示展示LogicalMode下路径渐变的填充效果，通过对比可以明显看出LogicalMode的填充坐标系为整个窗体：

void Widget::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);

    QPainter painter(this);

    painter.fillRect(this->rect(),QBrush(QColor(255,255,255)));
    painter.setRenderHint(QPainter::Antialiasing);//抗锯齿

    QLinearGradient gradient(0,0,0,150);
    gradient.setColorAt(0, Qt::red);
    gradient.setColorAt(1, Qt::blue);
    gradient.setCoordinateMode(QLinearGradient::CoordinateMode::LogicalMode);

    QBrush br(gradient);
    painter.setBrush(br);
//    painter.fillRect(this->rect(),br);

    painter.drawEllipse(0,0,this->width()/3,this->height()/3);

    painter.drawEllipse(this->width()/3,this->height()/3,this->width()/3,this->height()/3);
    painter.drawEllipse(this->width()*2/3,this->height()*2/3,this->width()/3,this->height()/3);
}

   

2、CoordinateMode::ObjectMode为在画图对象内进行渐变填充，即在所绘制的目标坐标系内进行渐变填充，以下为该模式下填充方式的展示：

void Widget::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);

    QPainter painter(this);

    painter.fillRect(this->rect(),QBrush(QColor(255,255,255)));
    painter.setRenderHint(QPainter::Antialiasing);//抗锯齿

    QLinearGradient gradient(0,0,0,1);
    gradient.setColorAt(0, Qt::red);
    gradient.setColorAt(1, Qt::blue);
    gradient.setCoordinateMode(QLinearGradient::CoordinateMode::ObjectMode);

    QBrush br(gradient);
    painter.setBrush(br);

    painter.drawEllipse(0,0,this->width()/3,this->height()/3);

    painter.drawEllipse(this->width()/3,this->height()/3,this->width()/3,this->height()/3);
    painter.drawEllipse(this->width()*2/3,this->height()*2/3,this->width()/3,this->height()/3);
}