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Port the game loop

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Summary

Shows how to implement a window for a Universal Windows Platform (UWP) game and how to bring over the game loop, including how to build an IFrameworkView to control a full-screen CoreWindow. Part 3 of the Port a simple Direct3D 9 app to DirectX 11 and UWP walkthrough.

Create a window

To set up a desktop window with a Direct3D 9 viewport, we had to implement the traditional windowing framework for desktop apps. We had to create an HWND, set the window size, provide a window processing callback, make it visible, and so on.

The UWP environment has a much simpler system. Instead of setting up a traditional window, a Microsoft Store game using DirectX implements IFrameworkView. This interface exists for DirectX apps and games to run directly in a CoreWindow inside the app container.

Note   Windows supplies managed pointers to resources such as the source application object and the CoreWindow. See Handle to Object Operator (^).

 

Your "main" class needs to inherit from IFrameworkView and implement the five IFrameworkView methods: Initialize, SetWindow, Load, Run, and Uninitialize. In addition to creating the IFrameworkView, which is (essentially) where your game will reside, you need to implement a factory class that creates an instance of your IFrameworkView. Your game still has an executable with a method called main(), but all main can do is use the factory to create the IFrameworkView instance.

Main function

//-----------------------------------------------------------------------------
// Required method for a DirectX-only app.
// The main function is only used to initialize the app's IFrameworkView class.
//-----------------------------------------------------------------------------
[Platform::MTAThread]
int main(Platform::Array<Platform::String^>^)
{
    auto direct3DApplicationSource = ref new Direct3DApplicationSource();
    CoreApplication::Run(direct3DApplicationSource);
    return 0;
}

IFrameworkView factory

//-----------------------------------------------------------------------------
// This class creates our IFrameworkView.
//-----------------------------------------------------------------------------
ref class Direct3DApplicationSource sealed : 
    Windows::ApplicationModel::Core::IFrameworkViewSource
{
public:
    virtual Windows::ApplicationModel::Core::IFrameworkView^ CreateView()
    {
        return ref new Cube11();
    };
};

Port the game loop

Let's look at the game loop from our Direct3D 9 implementation. This code exists in the app's main function. Each iteration of this loop processes a window message or renders a frame.

Game loop in Direct3D 9 desktop game

while(WM_QUIT != msg.message)
{
    // Process window events.
    // Use PeekMessage() so we can use idle time to render the scene. 
    bGotMsg = (PeekMessage(&msg, NULL, 0U, 0U, PM_REMOVE) != 0);

    if(bGotMsg)
    {
        // Translate and dispatch the message
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    else
    {
        // Render a new frame.
        // Render frames during idle time (when no messages are waiting).
        RenderFrame();
    }
}

The game loop is similar - but easier - in the UWP version of our game:

The game loop goes in the IFrameworkView::Run method (instead of main()) because our game functions within the IFrameworkView class.

Instead of implementing a message handling framework and calling PeekMessage, we can call the ProcessEvents method built in to our app window's CoreDispatcher. There's no need for the game loop to branch and handle messages - just call ProcessEvents and proceed.

Game loop in Direct3D 11 Microsoft Store game

// UWP apps should not exit. Use app lifecycle events instead.
while (true)
{
    // Process window events.
    auto dispatcher = CoreWindow::GetForCurrentThread()->Dispatcher;
    dispatcher->ProcessEvents(CoreProcessEventsOption::ProcessAllIfPresent);

    // Render a new frame.
    RenderFrame();
}

Now we have a UWP app that sets up the same basic graphics infrastructure, and renders the same colorful cube, as our DirectX 9 example.

Where do I go from here?

Bookmark the DirectX 11 porting FAQ.

The DirectX UWP templates include a robust Direct3D device infrastructure that's ready for use with your game. See Create a DirectX game project from a template for guidance on picking the right template.

Visit the following in-depth Microsoft Store game development articles: