QT 渐变

QPainter painter(canvas);   //widget_memwd作为画图对象？  
QPixmap m_pBg;
m_pBg.load("Resources/UI/bk_line.png");
QLinearGradient gradient(0, COLOR_GRADIENT, 0, 0);
gradient.setColorAt(0.0, QColor(82,211,238,0));
gradient.setColorAt(1.0, QColor(82,211,238,255));
painter.setRenderHint(QPainter::Antialiasing, true);
QBrush brush(gradient);
QBrush linerect(QColor(82,211,238,0));
QPen   penrect(linerect,1);
QBrush lineb(QColor(17,152,191));
QPen  penline(lineb,1);


painter.setBrush(brush);
painter.drawPixmap(canvas->rect(),m_pBg);
//横轴时间轴,按照2秒刻度
int dx = X_MAX - (serviceinfovt.size()*TIME_X_SCALE);
int px1 =dx;
int py1 = (COLOR_GRADIENT*(serviceinfovt[0].cpu_usage_/1000))/CPU_MAX;


for (int i=0;i<serviceinfovt.size();i++)
{
int cpupercent = (COLOR_GRADIENT*serviceinfovt[i].cpu_usage_/1000)/CPU_MAX;
QPointF points[4] = {
QPointF(px1, COLOR_GRADIENT),
QPointF(px1, COLOR_GRADIENT-py1),
QPointF(dx, COLOR_GRADIENT-cpupercent),
QPointF(dx, COLOR_GRADIENT),
};
painter.setPen(penrect);
painter.drawPolygon(points,4);


painter.setPen(penline);
painter.drawLine(dx,COLOR_GRADIENT-cpupercent,px1,COLOR_GRADIENT-py1);


px1 = dx;
py1 = cpupercent;


dx+=TIME_X_SCALE;
}