//Листинг 4.4. Оконная функция задачи "Ping-pong"

const int SPAN = 10;
#include <math.h>
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM
   lParam)
{
   PAINTSTRUCT ps;
   HDC hdc;
   int mx, my;
   static double mod, vx, vy, xt, yt;
   static HDC memDC;

   static HPEN hpen;
   static int x, y, cx, cy, scrx, scry;
   static HBITMAP hCircle;
   static bool play;
   switch (message)
   {
   case WM_CREATE:
      hpen = CreatePen(PS_SOLID, 4, RGB(255, 0, 0));
      hCircle = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_CIRCLE));
      hdc = GetDC(hWnd);
      memDC = CreateCompatibleDC(hdc);
      SelectObject(memDC, hCircle);
      ReleaseDC(hWnd, hdc);
      break;
   case WM_SIZE:
      scrx = LOWORD(lParam);
      scry = HIWORD(lParam);
      x = (cx = scrx/2) - 16;
      y = (cy = scry/2) - 16;
      break;
   case WM_LBUTTONDOWN:
      if (!play)
      { mx = LOWORD(lParam);
        my = HIWORD(lParam);
        vx = mx - cx;
        vy = my - cy;
        mod = sqrt(vx*vx+vy*vy);
        vx = vx/mod;
        vy = vy/mod;
        hdc = GetDC(hWnd);
        SelectObject(hdc, hpen);
        MoveToEx(hdc, cx, cy, 0);
        LineTo(hdc, mx, my);
        LineTo(hdc, mx - (vx - vy)*SPAN, my - (vy + vx)*SPAN);
        MoveToEx(hdc, mx - (vx + vy)*SPAN, my - (vy - vx)*SPAN, 0);
        LineTo(hdc, mx, my);
        ReleaseDC(hWnd, hdc);
        play = true;
      }
      break;
   case WM_TIMER:
      hdc = GetDC(hWnd);
      BitBlt(hdc, x, y, 32, 32, NULL, 0, 0, PATCOPY);

      if (x + 31 > scrx || x < 1) vx = -vx;
      if (y + 31 > scry || y < 1) vy = -vy;
      xt += vx*10;
      yt += vy*10;
      x = int(xt + 0.5);
      y = int(yt + 0.5);
      BitBlt(hdc, x, y, 32, 32, memDC, 0, 0, SRCCOPY);
      ReleaseDC(hWnd, hdc);
      break;
   case WM_COMMAND:
      switch (LOWORD(wParam))
      {
      case ID_PLAY_BEGIN:
      SetTimer(hWnd, 1, (int)(sqrt(double(cx*cx+cy*cy))/mod)*10, NULL);
      xt = x;
      yt = y;
      InvalidateRect(hWnd, NULL, TRUE);
      break;
   case ID_PLEY_END:
      KillTimer(hWnd, 1);
      x = cx - 16;
      y = cy - 16;
      InvalidateRect(hWnd, NULL, TRUE);
      play = false;
      break;
   case IDM_EXIT: DestroyWindow(hWnd); break;
   default: return DefWindowProc(hWnd, message, wParam, lParam);
   }
   break;
   case WM_PAINT:
      hdc = BeginPaint(hWnd, &ps);
         BitBlt(hdc, x, y, 32, 32, memDC, 0, 0, SRCCOPY);
         EndPaint(hWnd, &ps);
      break;
   case WM_DESTROY:
      DeleteDC(memDC);
      DeleteObject(hpen);
      PostQuitMessage(0);
      break;
   default: return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}