An Introduction to Windows Programming - Introduction to 3D Game Programming with DirectX 9.0 - page 374

destroyed. Our code is quite simple; when we receive a WM_LBUTTON-
DOWN message, we display a message box that prints out “Hello,
World”:
case WM_LBUTTONDOWN:
::MessageBox(0, "Hello, World", "Hello", MB_OK);
return 0;
When our window gets a WM_KEYDOWN message, we test what key was
pressed. The wParam passed into the window procedure specifies the
virtual key code of the specific key that was pressed. Think of virtual
key codes as an identifier for a particular key. The Windows header files
have a list of virtual key code constants that we can use to then test for
a particular key (for example, to test if the Escape key was pressed, we
use the virtual key code constant VK_ESCAPE ).
Note: Remember, the wParam and lParam parameters are used to
specify extra information about a particular message. For the WM_KEY-
DOWN message, the wParam specifies the virtual key code of the specific
key that was pressed. The MSDN library will specify the information
that the wParam and lParam parameters carry for each Windows
message.
case WM_KEYDOWN:
if( wParam == VK_ESCAPE )
::DestroyWindow(MainWindowHandle);
return 0;
When our window gets destroyed, we post a quit message (which ter-
minates the message loop).
case WM_DESTROY:
::PostQuitMessage(0);
return 0;
At the end of our window procedure, we call the DefWindowProc
function. This function is a default window procedure. In our Hello
World application, we only handle three messages; we use the default
behavior specified in DefWindowProc for all the other messages that
we receive but don't necessarily need to handle ourselves. For exam-
ple, Hello World can be minimized, maximized, resized, and closed.
This functionality is provided to us through the default window proce-
dure, as we do not handle the window messages to perform this
functionality. Note that DefWindowProc is a Win32 API function.
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