Invalidate的解释

Invalidates the entire client area.

这句话说的很有意思，就是使无效就是重绘。

 

void CBounceWnd::OnLButtonDown(UINT, CPoint point)
{
    Invalidate();

    CRect rcClient;
    GetClientRect(rcClient);

    point.x = min(point.x, rcClient.right - 2*m_sizeRadius.cx);
    point.x = max(point.x, 2*m_sizeRadius.cx);
    point.y = min(point.y, rcClient.bottom - 2*m_sizeRadius.cx);
    point.y = max(point.y, 2*m_sizeRadius.cy);

    m_ptCenter = point;
}