WM_PAINT function, how to call again?

Ok here is the situation. I loaded a bitmap to the screen using windows GDI. I did this in the WM_PAINT function. Now what I want to do is when a user clicks on a file menu, the screen must become all clear. My question is how do I call the WM_PAINT function again to clear the screen? If I just write:

Code:

case ID_FILE_NEW:

                     WM_PAINT;
		{
			// Just a note, never use a MessageBox from inside WM_PAINT
			// The box will cause more WM_PAINT messages and you'll probably end up
			// stuck in a loop

			BITMAP bm;
			PAINTSTRUCT ps;

			HDC hdc = BeginPaint(hwnd, &ps);

			HDC hdcMem = CreateCompatibleDC(hdc);
			HBITMAP hbmOld = SelectObject(hdcMem, Logobmp);

			GetObject(Logobmp, sizeof(bm), &bm);

			BitBlt(hdc, 100, 50, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
            BitBlt(hdc, 0, 0, 800, 600,hdc, 0, 0, WHITENESS);
			SelectObject(hdcMem, hbmOld);
			DeleteDC(hdcMem);
			EndPaint(hwnd, &ps);
		}

nothing happens, the white background does't copy over the picture. However if I write the same code in the WM_PAINT function than it does.

WM_PAINT is a message sent to your window, where you handle it is a case in a switch statement not a function allthough you could call a function in the WM_PAINT case.
You can either send the WM_PAINT message yourself with SendMessage or call UpdateWindow. You can also call InvalidateRect on your window but that might not send WM_PAINT right away.

hmm, is it possible to call an if statement within WM_PAINT such as:

Code:

case WM_PAINT:
		{
			// Just a note, never use a MessageBox from inside WM_PAINT
			// The box will cause more WM_PAINT messages and you'll probably end up
			// stuck in a loop

			BITMAP bm;
			PAINTSTRUCT ps;

			HDC hdc = BeginPaint(hwnd, &ps);

			HDC hdcMem = CreateCompatibleDC(hdc);
			HBITMAP hbmOld = SelectObject(hdcMem, Logobmp);

			GetObject(Logobmp, sizeof(bm), &bm);

			BitBlt(hdc, 100, 50, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
			if (ClrScreen >= 0){
             BitBlt(hdc, 0, 0, 800, 600,hdc, 0, 0, WHITENESS);
             }
                          

			SelectObject(hdcMem, hbmOld);
			DeleteDC(hdcMem);

			EndPaint(hwnd, &ps);
		}
		break;

And than set the int ClrScreen to something greater than 0 and call WM_PAIT again:

Code:

case ID_FILE_NEW:
                     ClrScreen = 1;
                     PostMessage(hwnd, WM_PAINT, 0, 0);

However this doesn't work either for some reason.

EDIT: got it working with InvalidateRect(hwnd, NULL, FALSE ); instead of postmessege