我用fillrectangle创建了个矩形，鼠标移动上去后没有触发cleardevice()

#include<graphics.h>
#include<conio.h>
void menu()
{

	initgraph(1200, 700); //加载图形化窗口
	MOUSEMSG m;
	m = GetMouseMsg();
	HWND hWnd = GetHWnd(); //获取当前窗口句柄
	LONG oldstyle = GetWindowLong(hWnd,