Bresenham 生成直線

void BresenhamLine(const QPointF& pt0,
                   const QPointF& pt1,
                   std::vector<QPointF> &line)
{
    double x=0.0,y=0.0,e=0.0;
    double x0=pt0.x();
    double y0=pt0.y();
    double x1=pt1.x();
    double y1=pt1.y();
    double dx=x1-x0;
    double dy=y1-y0;
    if(fabs(dy)<=fabs(dx))
    {
        if(x1<x0)
        {
            qSwap(x0,x1);
            qSwap(y0,y1);
        }
        dx=x1-x0;
        dy=y1-y0;
        if(y0<=y1)
        {
            e=-dx;
            x=x0;
            y=y0;
            for(int i=0;i<=dx;i++)
            {
                line.push_back(QPointF(x,y));
                x++;
                e+=2*dy;
                if(e>=0)
                {
                    y++;
                    e-=2*dx;
                }
            }
        }
        else
        {
            e=dx;
            x=x0;
            y=y0;
            for(int i=0;i<=dx;i++)
            {
                line.push_back(QPointF(x,y));
                x++;
                e+=2*dy;
                if (e<=0)
                {
                    --y;
                    e+=2*dx;
                }
            }
        }
    }
    else
    {
        if(y1<y0)
        {
            qSwap(x0,x1);
            qSwap(y0,y1);
        }
        dx=x1-x0;
        dy=y1-y0;
        if(x0<=x1)
        {
            e=-dy;
            x=x0;
            y=y0;
            for(int i=0;i<=dy;i++)
            {
                line.push_back(QPointF(x,y));
                y++;
                e+=2*dx;
                if(e>=0)
                {
                    x++;
                    e-=2*dy;
                }
            }
        }
        else
        {
            e=dy;
            x=x0;
            y=y0;
            for(int i=0;i<=dy;i++)
            {
                line.push_back(QPointF(x,y));
                y++;
                e+=2*dx;
                if(e<=0)
                {
                    --x;
                    e+=2*dy;
                }
            }
        }
    }
}