GRID_SIZE是什么意思？该怎么处理

void CsingleView::OnDraw(CDC* pDC)
{
    CsingleDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);
    if (!pDoc)
        return;

    // TODO: 在此处为本机数据添加绘制代码
    //取得客户区域，并转化为相对坐标
    CRect WndRect;
    this->GetWindowRect(&WndRect);
    this->ScreenToClient(&WndRect);

    CDC mdc;                //内存DC
    CBitmap bmp;            //临时位图，为内存DC提供绘图环境
    CPen FramePen;            //画矩形框使用画笔
    CPen PtPen;                //画点时使用的画笔
    CBrush BkBrush;            //背景画刷，灰色
    CBrush PtBrush;            //画点时用的画刷，红色

    //初始化GDI对象
    mdc.CreateCompatibleDC(pDC);
    bmp.CreateCompatibleBitmap(pDC,WndRect.Width(),WndRect.Height());
    mdc.SelectObject (&bmp);
    FramePen.CreatePen(PS_SOLID,3,RGB(0,0,0));
    mdc.SelectObject(&FramePen);
    BkBrush.CreateSolidBrush(RGB(128,128,128));

    //绘制矩形区域

    int width = MAX_X_NUM * GRID_SIZE, height = MAX_Y_NUM * GRID_SIZE;
    mdc.Rectangle(START_POS_X,START_POS_Y,width+START_POS_X,height+START_POS_Y);
    PtBrush.CreateSolidBrush(PS_SOLOD,1,RGB(0,0,0));
    mdc.SelectObject(&PtPen);
    PtBrush.CreateSolidBrush(RGB(255,0,0));
    mdc.SelectObject(&PtBrush);

    //枚举CSingleDoc类中的点集数据

    int i, j;
    for (i = 0; i<MAX_X_NUM; i++)
    {
        for (j = 0; j< MAX_Y_NUM;j++)
        {
            //检测指定点的状态，如果为TRUE则在指定位置绘制红点
            if (pDoc->GetGridStatus(i,j))
            {
                int x = START_POS_X + GRID_SIZE * i;
                int y = START_POS_Y + GRID_SIZE * j;
                mdc.Ellipse(x, y, x + GRID_SIZE, y + GRID_SIZE);
            }
        }
    }
    pDC->BitBlt( 0, 0, WndRect.Width(),WndRect.Height(), &mdc, 0, 0, SRCCOPY);


    //删除临时GDI对象
    bmp.DeleteObject();
    FramePen.DeleteObject();
    PtPen.DeleteObject();
    BkBrush.DeleteObject();
    PtBrush.DeleteObject();
    mdc.DeleteDC();
}