opening seperate window to display bitmaps

I'm currently designing a program that I want to open a seperate window and display a bitmap, when selected in a menu. I set up a menu and the child window and the bitmap but when ran and the menu selected it doesn't do anything. It acts likes I got nothing in the switch statment in the menu.
What i have is

Code:

case IDM_WD_568A:
hwndChild = CreateWindow (szChildClass, NULL,
               	WS_CHILDWINDOW | WS_VISIBLE, 0, 0, 282, 363, hwnd, 568A,
                  (HINSTANCE GetWindowLong(hwnd, GWL_HINSTANCE), NULL);

The childWndProc is:

Code:

LRESULT CALLBACK ChildWndProc (HWND hwnd, UINT message,
								WPARAM wParam, LPARAM lParam)
{

   static HBITMAP  hBitmap;
   static int      cxClient, cyClient, cxSource, cySource ;
   BITMAP          bitmap;
   HDC				 hdc, hdcmem;
   HINSTANCE		 hInstance ;
   int 				 x,y;
   PAINTSTRUCT 	 ps;

	switch (message)
   {
   	case WM_CREATE :
      hInstance = ((LPCREATESTRUCT) lParam)->hInstance;

      hBitmap = LoadBitmap ("childInstance", TEXT ("Wiring Diagram"));

      GetObject (hBitmap, sizeof (BITMAP), &bitmap);

      cxSource = bitmap.bmWidth;
      cySource = bitmap.bmHeight;

      return 0;

      case WM_PAINT:
      hdc = BeginPaint (hwnd, &ps) ;
      hdcmem = CreateCompatibleDC (hdc) ;
      SelectObject (hdcmem, hBitmap);
      for (y = 0 ; y < cyClient ; y += cySource)
      for (x = 0 ; x < cxClient ; x += cxSource)
      {
      	BitBlt (hdc, x, y, cxSource, cySource, hdcmem, 0, 0, SRCCOPY) ;
      }

      DeleteDC (hdcmem);
      EndPaint (hwnd, &ps);
      return 0;

   	case WM_DESTROY:
      DeleteObject(hBitmap);
   	return 0;
   }
}

What am I doing wrong?

Ray Koons

PS..I used to post ALOT here like 2 years ago but to a hiatus from programming but am starting to get back into it.

I guess using 568A as child window identifier may be the problem?

Try it without the WS_CHILDWINDOW flag. On another note, that flag has the same value as WS_CHILD, so you needn't type those 6 extra characters.

Originally posted by bennyandthejets
Try it without the WS_CHILDWINDOW flag. On another note, that flag has the same value as WS_CHILD, so you needn't type those 6 extra characters.

I tried that, didn't change anything. I also changed the name of the child window like lobo said, still no effect :-(

Try putting a call to MessageBox right before the CreateWindow code to make sure that the CreateWindow code is being reached.

message box comes up but no childwindow

Try changing the 2nd parameter in CreateWindow to TEXT( "" ).

I never see the point in using TEXT(). Just look at the definition. It has absolutely no effect whatsoever on the parameter passed, it's exactly the same.

I just noticed that in this code, there is an imbalance of brackets. It should have caused a compile error.

Code:

hwndChild = CreateWindow (szChildClass, NULL,
               	WS_CHILDWINDOW | WS_VISIBLE, 0, 0, 282, 363, hwnd, 568A,
                  (HINSTANCE GetWindowLong(hwnd, GWL_HINSTANCE), //Need another closing bracket here
NULL);

I don't see how it could compile with this error.

The bracket belongs after the HINSTANCE (assuming it was not a typo on the OP's behalf):

Code:

hwndChild = CreateWindow (szChildClass, NULL,
               	WS_CHILDWINDOW | WS_VISIBLE, 0, 0, 282, 363, hwnd, 568A,
                  (HINSTANCE) /* Added missing closing bracket */GetWindowLongPtr(hwnd, GWL_HINSTANCE), NULL);

Life is a lot easier if you have an error number:

Code:

if (hwndChild == NULL) {
     char buf[256];
     sprintf(buf, "CreateWindow failed with %d", GetLastError());
     MessageBoxA(NULL, buf, NULL, 0);
}

I never see the point in using TEXT(). Just look at the definition. It has absolutely no effect whatsoever on the parameter passed, it's exactly the same.

You're going to get a rude shock when you start producing unicode compatible apps. :-) The TEXT macro causes a string literal to be a normal 8-bit string when unicode is not defined and a wide character string when unicode is defined.

Code:

#ifdef UNICODE
#define TEXT(string) L##string
#else
#define TEXT(string) string
#endif

You should read a tutorial on making your apps unicode compatible as it will save a lot of trouble down the track. For now, it is a good idea to use the TEXT macro and use the LPTSTR and TCHAR types instead of LPSTR and char types repspectively.

Child windows can't have menus.

MSDN
"WS_CHILD
Creates a child window. A window with this style cannot have a menu bar. This style cannot be used with the WS_POPUP style."

The resource ID is an int so yours, ending in an A, is invalid. IF thats what you called the menu then use MAKEINTRESOURCE()

If you specify the WS_CHILD then the HMENU param is interpreted as the windows int resource ID.

Your paint is going to be slow as you do all the drawing after the OS has called for a paint.
You have a GDI leak as the bitmap is selected into a HDC, not selected out again. This will prevent the HDC from being deleted as it has not been returned to its default state.
The bitmap will also not delete as it is still selected into a HDC (though this may be taken care of by the OS as the HDC has lost scope)

PS if you are going to open a window to display bitmaps of differing size look at

AdjustWindowRect()

I have posted examples of how to use this to resize the window to the image size.

The error code is 0.
This is my now reformed code:

Code:

          case IDM_WD_568A:
               MessageBox (NULL, TEXT  ("The menu works."), TEXT ("Hellomsg")
               	, 0);
     				hwndChild = CreateWindow ("Child_SCTS", TEXT("Wiring diagram"),
               	WS_CHILDWINDOW | WS_VISIBLE, 0, 0, 282, 363, hwnd, MAKEINTRESOURCE("568a"),
                  TEXT("hInstance"), NULL);

               if (hwndChild == NULL) {
     					char buf[256];
     					sprintf(buf, "CreateWindow failed with %d", GetLastError());
     					MessageBoxA(NULL, buf, NULL, 0);
					}
               return 0;

I haven't changed the childwndproc so Im not gonna repost that. I get the message box to come up so it hase to be something in the createwindow call but I can't see anything wrong. Also when creating a child window the ninth parameter of the createwindow call is the handle to the child window. There is no menu and its impossible to have a menu in a child window.

Something is missing...

return DefWindowProc(...);

Don't you hate that? We should make a checklist of reasons why window creation fails and post it on the FAQ board.

I was missing that but Im still getting the same result.
The WndChildProc now looks like this:

Code:

LRESULT CALLBACK ChildWndProc (HWND hwnd, UINT message,
								WPARAM wParam, LPARAM lParam)
{

   static HBITMAP  hBitmap;
   static int      cxClient, cyClient, cxSource, cySource ;
   BITMAP          bitmap;
   HDC				 hdc, hdcmem;
   HINSTANCE		 hInstance ;
   int 				 x,y;
   PAINTSTRUCT 	 ps;

	switch (message)
   {
   	case WM_CREATE :
      hInstance = ((LPCREATESTRUCT) lParam)->hInstance;

      hBitmap = LoadBitmap ("childInstance", TEXT ("Wiring Diagram"));

      GetObject (hBitmap, sizeof (BITMAP), &bitmap);

      cxSource = bitmap.bmWidth;
      cySource = bitmap.bmHeight;

      return 0;

      case WM_PAINT:
      hdc = BeginPaint (hwnd, &ps) ;
      hdcmem = CreateCompatibleDC (hdc) ;
      SelectObject (hdcmem, hBitmap);
      for (y = 0 ; y < cyClient ; y += cySource)
      for (x = 0 ; x < cxClient ; x += cxSource)
      {
      	BitBlt (hdc, x, y, cxSource, cySource, hdcmem, 0, 0, SRCCOPY) ;
      }

      DeleteDC (hdcmem);
      EndPaint (hwnd, &ps);
      return 0;

   	case WM_DESTROY:
      DeleteObject(hBitmap);
   	return 0;
   }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}

I fixed up some of the WM_CREATE message but to no avail. This is really agrivatig me now.

Code:

LRESULT CALLBACK ChildWndProc (HWND hwnd, UINT message,
								WPARAM wParam, LPARAM lParam)
{

   static HBITMAP  hBitmap;
   static int      cxClient, cyClient, cxSource, cySource ;
   BITMAP          bitmap;
   HDC				 hdc, hdcmem;
   HINSTANCE		 hInstance;
   int 				 x,y;
   PAINTSTRUCT 	 ps;

	switch (message)
   {
   	case WM_CREATE :
      hInstance = ((LPCREATESTRUCT) lParam)->hInstance;

      hBitmap = LoadBitmap (hInstance,MAKEINTRESOURCE("IDB_568a"));

      if (hBitmap == NULL) {
     	char buf[256];
     	sprintf(buf, "LoadBitmap failed with %d", GetLastError());
     	MessageBoxA(NULL, buf, NULL, 0);
		}

      GetObject (hBitmap, sizeof (BITMAP), &bitmap);

      cxSource = bitmap.bmWidth;
      cySource = bitmap.bmHeight;

      return 0;

      case WM_PAINT:
      hdc = BeginPaint (hwnd, &ps) ;
      hdcmem = CreateCompatibleDC (hdc) ;
      SelectObject (hdcmem, hBitmap);
      for (y = 0 ; y < cyClient ; y += cySource)
      for (x = 0 ; x < cxClient ; x += cxSource)
      {
      	BitBlt (hdc, x, y, cxSource, cySource, hdcmem, 0, 0, SRCCOPY) ;
      }

      DeleteDC (hdcmem);
      EndPaint (hwnd, &ps);
      return 0;

   	case WM_DESTROY:
      DeleteObject(hBitmap);
   	return 0;
   }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}

Could you post the code that registers the window class "Child_SCTS"?