QT利用QPainter绘制三维饼状图

private:
    void paintEvent( QPaintEvent* e);

void Widget::paintEvent( QPaintEvent* e)
{
    int start=240;//定义起始角度
    int ang=30;//定义角度范围

    QPainter painter(this);
    // 去除画笔
    painter.setPen(Qt::NoPen);
    // 设置反锯齿
    painter.setRenderHint(QPainter::Antialiasing);
    //三维饼状图
    // 顶层圆面
    QRectF rect_top(10.0, 20.0, 280.0, 160.0);
    // 底层圆面(宽高相同,y在顶层圆面下方40处)
    QRectF rect_bottom(10.0, 60.0, 280.0, 160.0);
    // 中间矩形
    QRectF rect_midd(10.0, 100.0, 280.0, 40.0);
    // 扇形起始角度
    int startAngle = start * 16;      //从230度
    // 扇形覆盖范围
    int spanAngle = ang * 16;

    painter.setBrush(QColor(97,35,35,255));//饼状图高度颜色
    // 绘制底层圆面
    painter.drawEllipse(rect_bottom);
    // 绘制中间矩形
    painter.drawRect(rect_midd);

    painter.setBrush(QColor(Qt::darkYellow));//饼状图占比高度颜色
    // 绘制底层扇形
    painter.drawPie(rect_bottom, startAngle, spanAngle);

    // 扇形的弦与弧的交点
    double pi = 3.1415926;
    double dx1 = rect_top.width() * 0.5 * cos(start * pi / 180);
    double dy1 = rect_top.height() * 0.5 * sin(start * pi / 180);

    double dx2 = rect_top.width() * 0.5 * cos((start+ang) * pi / 180);
    double dy2 = rect_top.height() * 0.5 * sin((start+ang) * pi / 180);

    // 求交点的坐标值
    QPointF posBackCenter = QPointF(rect_top.center());
    double dX1 = posBackCenter.x() + dx1 + 0.5;
    double dY1 = posBackCenter.y() - dy1 + 0.5;

    double dX2 = posBackCenter.x() + dx2 + 0.5;
    double dY2 = posBackCenter.y() - dy2 + 0.5;

        // 记录交点
        QPointF topLeft = QPointF(dX1, dY1);
        QPointF bottomRight = QPointF(dX2, dY2) + QPointF(0,40);
        QPointF bottomLeft = topLeft + QPointF(0,40);
        painter.setBrush(QColor(Qt::darkYellow));

        // 绘制连接扇形的区域
        QPolyGonF path;
        path << topLeft << QPointF(dX2,dY2) << bottomRight << bottomLeft;
        painter.drawPolygon(path);

        // 绘制顶层圆面
        painter.setBrush(QColor(156,56,56,255));
        painter.drawEllipse(rect_top);

        // 绘制顶层扇形
        painter.setBrush(QColor(Qt::yellow));
        painter.drawPie(rect_top, startAngle, spanAngle);

    QWidget::paintEvent(e);
}