Step 3: Handling System Messages

After you have created the application window and initialized Microsoft?Direct3D? you are ready to render the scene. In most cases, Microsoft Windows?applications monitor system messages in their message loop, and they render frames whenever no messages are in the queue. However, the CreateDevice sample project waits until a WM_PAINT message is in the queue, telling the application that it needs to redraw all or part of its window.

// The message loop.
MSG msg; 
while( GetMessage( &msg, NULL, 0, 0 ) )
{
    TranslateMessage( &msg );
    DispatchMessage( &msg );
}

Each time the loop runs, DispatchMessage calls MsgProc, which handles messages in the queue. When WM_PAINT is queued, the application calls Render, the application-defined function that will redraw the window. Then the Microsoft Win32?function ValidateRect is called to validate the entire client area.

The sample code for the message-handling function is shown below.

LRESULT WINAPI MsgProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
    switch( msg )
    {
        case WM_DESTROY:
            PostQuitMessage( 0 );
            return 0;

        case WM_PAINT:
            Render();
            ValidateRect( hWnd, NULL );
            return 0;
    }

    return DefWindowProc( hWnd, msg, wParam, lParam );
}

Now that the application handles system messages, the next step is to render the display, as described in Step 4: Rendering and Displaying a Scene.