Datepicker control

#include    <windows.h>

#define     MINSIZE        50 // The minimal width and height a childwindow should have
#define     SBS            2  // Short for SplitterBarSize

LRESULT CALLBACK WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
   static   HWND           hwndChild1, hwndChild2, hwndChild3;
   static   CREATESTRUCT   *cs;
   static   HCURSOR        hcSizeNS, hcSizeEW, hcArrow;
   static   int            xDiv, yDiv;
   static   BOOL           xSizing, ySizing;

   int                     xPos, yPos;
   RECT                    rect, focusrect;
   HDC                     hdc;

   switch(iMsg)
   {
   case WM_CREATE :
      cs = (CREATESTRUCT *)lParam;
      xDiv = 300;
      yDiv = 300;

      hwndChild1 = CreateWindowEx(WS_EX_CLIENTEDGE, "Pane 1", "Child 1",
                     WS_CHILD | WS_VISIBLE | WS_CLIPCHILDREN,
                     0, 0, 0, 0, hwnd, NULL, cs->hInstance, NULL);
      hwndChild2 = CreateWindowEx(WS_EX_CLIENTEDGE, "Pane 2", "Child 2",
                     WS_CHILD | WS_VISIBLE | WS_CLIPCHILDREN,
                     0, 0, 0, 0, hwnd, NULL, cs->hInstance, NULL);
      hwndChild3 = CreateWindowEx(WS_EX_CLIENTEDGE, "Pane 3", "Child 3",
                     WS_CHILD | WS_VISIBLE | WS_CLIPCHILDREN,
                     0, 0, 0, 0, hwnd, NULL, cs->hInstance, NULL);

      hcSizeNS = LoadCursor(NULL, IDC_SIZENS);
      hcSizeEW = LoadCursor(NULL, IDC_SIZEWE);
      hcArrow  = LoadCursor(NULL, IDC_ARROW);
      break;

   case WM_SIZE :
      GetClientRect(hwnd, &rect);
      // Make sure splitterbars are visible
      if(xDiv > rect.right - MINSIZE)
      {
         xDiv = rect.right - MINSIZE;
      }
      else if(xDiv < MINSIZE)
      {
         xDiv = MINSIZE;
      }
      if(yDiv > rect.bottom - MINSIZE)
      {
         yDiv = rect.bottom - MINSIZE;
      }
      else if(yDiv < MINSIZE)
      {
         yDiv = MINSIZE;
      }
      MoveWindow(hwndChild1, rect.left, rect.top + 1,
                  rect.left + xDiv - SBS, rect.top + yDiv - SBS, FALSE);
      MoveWindow(hwndChild2, rect.left + xDiv + SBS,
                  rect.top + 1, rect.right - rect.left - xDiv - SBS, rect.top + yDiv - SBS, FALSE);
      MoveWindow(hwndChild3, rect.left, rect.top + yDiv + SBS,
                  rect.right - rect.left, rect.bottom - rect. top - yDiv - SBS, FALSE);
      InvalidateRect(hwnd, &rect, TRUE);
      break;

   case WM_LBUTTONDOWN :
      xPos = (int)LOWORD(lParam);
      yPos = (int)HIWORD(lParam);

      xSizing = (xPos > xDiv - SBS && xPos < xDiv + SBS);
      ySizing = (yPos > yDiv - SBS && yPos < yDiv + SBS);

      if(xSizing || ySizing)
      {
         SetCapture(hwnd); // Track movement of the mousepointer
         if(xSizing)
         {
            SetCursor(hcSizeEW);
         }
         else if(ySizing)
         {
            SetCursor(hcSizeNS);
         }
      }
      break;

   case WM_LBUTTONUP :
      if(xSizing || ySizing)
      {
         ReleaseCapture();
         hdc = GetDC(hwnd);
         GetClientRect(hwnd, &rect);
         if(xSizing)
         {
            SetRect(&focusrect, xDiv - SBS, rect.top, xDiv + SBS, yDiv);
            DrawFocusRect(hdc, &focusrect);
            xSizing = FALSE;
         }
         if(ySizing)
         {
            SetRect(&focusrect, rect.left + 1, yDiv - SBS, rect.right, yDiv + SBS);
            DrawFocusRect(hdc, &focusrect);
            ySizing = FALSE;
         }
         ReleaseDC(hwnd, hdc);
      }
      // Post a size message so the childwindows get their new size
      PostMessage(hwnd, WM_SIZE, 0, 0);
      break;

   case WM_MOUSEMOVE :
      xPos = (int)LOWORD(lParam);
      yPos = (int)HIWORD(lParam);

      if(wParam == MK_LBUTTON)   // Is one of the splitterbars being moved?
      {
         if(xSizing || ySizing)
         {
            hdc = GetDC(hwnd);
            GetClientRect(hwnd, &rect);

            if(xSizing)
            {
               SetRect(&focusrect, xDiv - SBS, rect.top, xDiv + SBS, yDiv);
               DrawFocusRect(hdc, &focusrect);

               xDiv = xPos;

               SetRect(&focusrect, xDiv - SBS, rect.top, xDiv + SBS, yDiv);
               DrawFocusRect(hdc, &focusrect);
            }
            if(ySizing)
            {
               SetRect(&focusrect, rect.left + 1, yDiv - SBS, rect.right, yDiv + SBS);
               DrawFocusRect(hdc, &focusrect);

               yDiv = yPos;

               SetRect(&focusrect, rect.left + 1, yDiv - SBS, rect.right, yDiv + SBS);
               DrawFocusRect(hdc, &focusrect);
            }
            ReleaseDC(hwnd, hdc);
         }
         break;   // Leave
      }

      if( (xPos > xDiv - SBS && xPos < xDiv + SBS) && GetCursor() != hcSizeEW )
      {
         SetCursor(hcSizeEW); // hovering above the vertical splitterbar
      }
      else if( (yPos > yDiv - SBS && yPos < yDiv + SBS) && GetCursor() != hcSizeNS )
      {
         SetCursor(hcSizeNS); // hovering above the horizontal splitterbar
      }
      else if(GetCursor() != hcArrow)
      {
         SetCursor(hcArrow);  // not hovering above a splitterbar
      }
      break;

   case WM_CLOSE :
      DestroyWindow(hwnd);
      break;

   case WM_DESTROY :
      PostQuitMessage(0);
      break;
   }
   return DefWindowProc(hwnd, iMsg, wParam, lParam);
}

LRESULT CALLBACK Child1WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
   switch(iMsg)
   {
   case WM_CREATE :
      break;
   }
   return DefWindowProc(hwnd, iMsg, wParam, lParam);
}

LRESULT CALLBACK Child2WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
   switch(iMsg)
   {
   case WM_CREATE :
      break;
   }
   return DefWindowProc(hwnd, iMsg, wParam, lParam);
}

LRESULT CALLBACK Child3WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{
   switch(iMsg)
   {
   case WM_CREATE :
      break;
   }
   return DefWindowProc(hwnd, iMsg, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
   HWND        hwnd;
   MSG         msg;
   WNDCLASS    wndclass;
   char        szAppName[] = "SplitterApp";

   wndclass.style         = 0;
   wndclass.lpfnWndProc   = WndProc;
   wndclass.cbClsExtra    = 0;
   wndclass.cbWndExtra    = 0;
   wndclass.hInstance     = hInstance;
   wndclass.hIcon         = LoadIcon(hInstance, szAppName);
   wndclass.hCursor       = LoadCursor(NULL, IDC_ARROW);
   wndclass.hbrBackground = (HBRUSH)(COLOR_BTNFACE + 1);
   wndclass.lpszMenuName  = szAppName;
   wndclass.lpszClassName = szAppName;
   RegisterClass(&wndclass);

   wndclass.lpfnWndProc   = Child1WndProc;
   wndclass.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
   wndclass.lpszClassName = "Pane 1";
   RegisterClass(&wndclass);

   wndclass.lpfnWndProc   = Child2WndProc;
   wndclass.lpszClassName = "Pane 2";
   RegisterClass(&wndclass);

   wndclass.lpfnWndProc   = Child3WndProc;
   wndclass.lpszClassName = "Pane 3";
   RegisterClass(&wndclass);

   hwnd = CreateWindow(szAppName, szAppName, WS_OVERLAPPEDWINDOW | SW_MAXIMIZE | WS_VISIBLE,
                        0, 0, 600, 500, NULL, NULL, hInstance, szCmdLine);

   while (GetMessage(&msg, NULL, 0, 0))
   {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
   }
   return (int)msg.wParam;
}