윈도우즈 프로그램이 굴러가는 정현 곡선 (2)

//               ，           
//    2*NUM     。
#include <windows.h>
#include <math.h>

#define ID_TIMER 1
#define NUM 1000
#define STEP 10//       
#define TWOPI (2 * 3.14159)

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain ( HINSTANCE hInstance, HINSTANCE hPrevInstance,
   PSTR szCmdLine, int iCmdShow)
{
 static TCHAR szAppName[] = TEXT ("SineWave") ;
 HWND   hwnd ;
 MSG    msg ;
 WNDCLASS  wndclass ;
     
 wndclass.style  = CS_HREDRAW | CS_VREDRAW ;
 wndclass.lpfnWndProc= WndProc ;
 wndclass.cbClsExtra = 0 ;
 wndclass.cbWndExtra = 0 ;
 wndclass.hInstance = hInstance ;
 wndclass.hIcon  = LoadIcon (NULL, IDI_APPLICATION) ;
 wndclass.hCursor = LoadCursor (NULL, IDC_ARROW) ;
 wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
 wndclass.lpszMenuName  = NULL ;
 wndclass.lpszClassName = szAppName ;
          
 if (!RegisterClass (&wndclass))
 {
   MessageBox ( NULL, TEXT ("Program requires Windows NT!"), 
   szAppName, MB_ICONERROR) ;
   return 0 ;
 }
     
 hwnd = CreateWindow ( szAppName, TEXT ("Sine Wave Using Polyline"),
    WS_OVERLAPPEDWINDOW,
    CW_USEDEFAULT, CW_USEDEFAULT,
    CW_USEDEFAULT, CW_USEDEFAULT,
    NULL, NULL, hInstance, NULL) ;
 ShowWindow (hwnd, iCmdShow) ;
 UpdateWindow (hwnd) ;
     
 while (GetMessage (&msg, NULL, 0, 0)){
  TranslateMessage (&msg) ;
  DispatchMessage (&msg) ;
 }
  return msg.wParam ;
}

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){
 static int  cxClient, cyClient ;
 HDC         hdc ;
 int         i;
 PAINTSTRUCT ps ;
 static POINT       apt [2*NUM] ;
 static HPEN hPen1,hPen2;
 static int step;
     
 switch (message)
 {
    case WM_SIZE:
       cxClient = LOWORD(lParam);
       cyClient = HIWORD(lParam);
   
   for(i = 0; i < 2 * NUM; i++)
   {
    apt[i].x = (int)(i * cxClient / NUM);
    apt[i].y = (int) (cyClient * (1 - sin(TWOPI * i / NUM)) / 2);
   }
   return 0;
  case WM_CREATE:
   hPen1 = CreatePen(PS_SOLID,4,RGB(255,0,0));
   hPen2 = CreatePen(PS_SOLID,2,RGB(0,255,0));
   SetTimer(hwnd,ID_TIMER,100,NULL);
   return 0;

  case WM_TIMER:
   step= (step+STEP) % NUM;
   InvalidateRect(hwnd,NULL,true);
    UpdateWindow(hwnd);
      return 0;
  case  WM_PAINT:
     hdc = BeginPaint(hwnd,&ps);
           SetViewportOrgEx(hdc,-step*cxClient/NUM,0,NULL);
     SelectObject(hdc,hPen1);
     MoveToEx(hdc,-step*cxClient/NUM,cyClient/2,NULL);
     LineTo(hdc,cxClient+step*cxClient/NUM,cyClient/2);
     SelectObject(hdc,hPen2);
     Polyline (hdc, apt+step, NUM) ;
     EndPaint(hwnd,&ps);
     return 0;

    case WM_DESTROY:
     PostQuitMessage(0);
     KillTimer(hwnd,ID_TIMER);
     DeleteObject(hPen1);
     DeleteObject(hPen2);
     return 0;  
    }
 return DefWindowProc(hwnd,message,wParam,lParam);
}