使用EasyX实现画图软件中画出矩形的效果

#include <easyx.h>
#include<stdio.h>
int main()
{
  initgraph(1120, 700);
  setbkcolor(WHITE);
  cleardevice();
  setlinecolor(BLACK);
  int L, T, R, B;
  ExMessage msg;
  while (1)//先固定1个点的(x,y)
  {
    if (peekmessage(&msg, EX_MOUSE))
    {
      if (msg.message == WM_LBUTTONDOWN)
      {
        L = msg.x;
        T = msg.y;
        break;
      }
    }
  }
  while (1)
  {
    if (peekmessage(&msg, EX_MOUSE))
    {
      R = msg.x;
      B = msg.y;
      cleardevice();
      rectangle(L, T, R, B);//左上角(L,T) 右下角(R,B)
      if (msg.message == WM_LBUTTONUP)
      {
        break;
      }
    }
  }
  getmessage(EX_KEY);
  return 0;
}