COLORREF circle_color =  RGB(0, 105, 255);



	//获取窗口DC
	HDC hdc = GetDC(hWnd_);

	//背景色透明
	SetBkMode(hdc, TRANSPARENT);


	// 这里的像素是相对窗体来说的， 而不是屏幕坐标，
	HPEN pen = CreatePen(PS_SOLID, 3, circle_color);
	SelectObject(hdc, pen);
	//Ellipse(hdc, center_x_in_form - CIRCLE_RADIUS, center_y_in_form - CIRCLE_RADIUS, 
	//				center_x_in_form + CIRCLE_RADIUS , center_y_in_form + CIRCLE_RADIUS);

	SetROP2(hdc, R2_NOTXORPEN);   // 第一次回圈，  重新调用一次 就 删除原来的圈 去掉这一句就是正常画圈
	Ellipse(hdc, center_x_in_form - CIRCLE_RADIUS, center_y_in_form - CIRCLE_RADIUS, 
				center_x_in_form + CIRCLE_RADIUS , center_y_in_form + CIRCLE_RADIUS);

	//释放句柄DC
	ReleaseDC(hWnd_, hdc);