Fall Fury: Part 1 - Introduction
- Posted: Jan 23, 2013 at 3:56 PM
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In late May, I arrived in Redmond to work as an intern on the Channel9 team. I had the freedom to choose what I was going to work on, so I decided to challenge myself and work outside my comfort zone, utilizing less C# and managed code and more C++ and DirectX. To do so, I decided to highlight the capabilities of Windows 8—that’s how FallFury was born.
FallFury is a 2D platformer in which the player controls a falling bear, trying to avoid obstacles, dodge missiles, and destroy monsters as the bear falls. The project incorporates several of the new Windows 8 APIs, including the accelerometer and touch as well as integrations with core OS capabilities such as settings and share charms. Additionally, the project leverages the most exacting addition to the Visual Studio development environment—hybrid application development with XAML, C++, and DirectX.
Check out the video for this article at http://channel9.msdn.com/Series/FallFury/Part-1-Introduction. For a complete, offline version of this series, you may download a nicely formatted PDF of all the articles.
From the outset, Rick Barraza and I decided that since our target audience was composed of both kids and adults, the main character had to be familiar to both groups. Teddy bears turned out to be the best choice. Rick spent a day creating tens of potential bear drawings—out of which I had to choose one:
As the bear’s fall progresses, the character encounters a variety of obstacles dependent on the level type and complexity. Those obstacles should of course be avoided, so as the user tilts the device, the character in the game moves in the associated direction.
The design of the project took a week, and during this time the following items were determined and conceptualized. Considerations for both tablet and desktop environments directed our decisions:
· The main character layout.
· The way the game progresses as the character falls down.
· How the user interacts with the game in a wide variety of possible scenarios.
· What the game screens look like.
· What the menu system interaction looks like.
· How the game looks in different screen modes and on different device types.
· Some of the bonuses that the main character can pick up during free fall.
· What happens when the user progresses through the game and iterates through levels.
· What is shared and how this is accomplished.
As the game ideas were outlined, Arturo Toledo, the designer behind ux.artu.tv, was brought on to create the game assets. Then the core design decisions were made and we jumped into the development process.
You will need to download and install Microsoft Visual Studio 2012 Express for Windows 8 in order to be able to follow the steps that I am describing in this series. The development has to be done on Windows 8, because the end result is a Windows Store application that relies on Windows 8 APIs. Though specific hardware is not required, both ARM and x86 devices will work well, so whether you have a Microsoft Surface RT or Samsung Series 7 slate, you will be able to test the code when you have the opportunity.
To get started, open Visual Studio 2012 and select the C++ project types. You will notice that there are several options you can choose from. You want to create a Windows Store application, so choose the appropriate category. Windows Store applications run in a sandbox, outside the boundaries of the standard .NET runtime.
Next, select the Direct2D (XAML) app type from the project list. This is a new application type introduced in Visual Studio 2012 that allows developers to combine native DirectX graphics with XAML overlays. Do not be confused by the fact that there is a Direct2D in the name—you can still invoke DirectX capabilities supported in the WinRT sandbox:
At this point you might be wondering, why choose a hybrid application instead of a fully-native project? The reason behind this decision is that is allows the developer to focus more on fine-tuning the gameplay instead of creating the UI core in pure DirectX. Because XAML is a part of the game, we can create dynamic UI layouts for the HUD, settings charm and menus without touching the graphical backbone. It is possible to do the same directly through DirectX and was a perfect approach for FallFury, considering the time constraints and the fact that I needed minimal UI overlays. Most of the graphics were already processed through the DirectX pipeline, so I did not have to invest significant resources and time into designing low-level structures for the interactivity layer.
FallFury uses XAML for the following:
When you create the project, a default infrastructure that prints text on the screen—both through Direct2D and XAML—is available. Direct2D is a subset of DirectX APIs and facilitates hardware-accelerated 2D graphics processing. It is used to create basic geometry elements and text. Since I am here working mostly with XAML, I am not going to cover Direct2D in-depth in this article:
I will go into more details regarding the XAML and DirectX interaction model later in the series, but for now, take a look at which parts of the project you have available. First and foremost, you probably notice the combination of both C++ source and header files and DirectXPage.xaml. Starting with Visual Studio 2012, you are now able to create XAML applications in C++. So even if you are an experienced C++ developer who never worked with the Extensible Application Markup Language, you can create the product core in your familiar environment and either import existing XAML structures or delegate the XAML writing to a designer.
If you open the XAML page, you will notice one significant change that you haven’t experienced in standard XAML applications, such as WPF or Silverlight for Windows Phone:
<SwapChainBackgroundPanel x:Name="SwapChainPanel" PointerMoved="OnPointerMoved" PointerReleased="OnPointerReleased"> <TextBlock x:Name="SimpleTextBlock" HorizontalAlignment="Center" FontSize="42" Height="72" Text="Hello, XAML!" Margin="0,0,0,50"/> </SwapChainBackgroundPanel>
A SwapChainBackgroundPanel is a component that lets the developer overlay XAML on top of the core DirectX-based experience. Look, for example, at the FallFury main menu as the game runs in landscape mode:
The menu buttons, the label and the side curtains are designed and rendered entirely in XAML. The clouds in the background, as well as the teddy bear, are rendered directly through the DirectX stack. The end-user does not notice any difference in the way these elements interact or are displayed. From a development perspective, however, there are several conditions that must be met.
There can only be one instance of SwapChainBackgroundPanel per app. Therefore, you can have only one overlaid XAML controls set. This does not mean that you can’t have multiple controls, but it implies that to do so you have to implement a control management flow that handles content adaptation. For example, if I invoke the pause state in the game, I don’t show the HUD but rather the screen-specific controls that let me resume or abandon the game and the PAUSE label. This switch needs to be handled on both the DirectX and XAML because a state change affects what is shown on the screen and what behaviors are tracked. As you will see through this series, this is not too hard to implement with a helper class that will store the global game state, that can be accessed from anywhere in the game.
When using SwapChainBackgroundPanel, remember that XAML is in all cases overlaid on top of the DirectX renders. So, no matter what controls you are using, those will always be placed on top of what DirectX shows to the user. For more details about how DirectX and XAML interoperate, check out this MSDN article.
As with any other game, there is not only code involved in production—there are also sound and graphical assets that create a unique experience for the user. FallFury includes a wide variety of graphical assets designed by Toledo Design as well as audio created by David Walliman.
It is important that all graphical resource requirements are established at the very beginning of development. As I mentioned in the Design section of this article, I had to put together a list of all the game screens, power-ups, obstacles, backgrounds, character states and possible particles that were generated from a texture. That way, when the designer started creating the assets, all components blended together well and their styles were compatible with the vision of the game.
While working on the assets, Arturo Toledo created multiple variations of the same set up that showed how assets integrate in different game conditions:
As you follow this series, you will not have to create your own game assets—we at Coding4Fun decided to provide all graphical and audio assets, which you can download at http://fallfury.codeplex.com/. We not only provided you with the final PNG and DDS files, but also with the raw assets that can be used in Microsoft Expression Design and Adobe Illustrator. Let’s take a look at what is in the package.
You will notice that the project Assets folder is split in several subfolders. All these assets are used mostly in the XAML layer or in game conditions where texture/sound processing is not necessary. There is also an additional asset folder I will discuss later.
All graphical assets mentioned here are PNG resources. The way I structured the game, some elements are larger than the others and I needed to take some measures to cut down on the package size. PNGs are fairly well-sized without much quality loss compared to raw images. At the beginning of the development process, all graphics were stored in DDS files.
DirectDraw Surface, or DDS, is a file format developed by Microsoft that helps developers optimize some of the graphics by avoiding re-compression performance loss. One of the benefits of using DDS files is the fact that whenever they are processed by the GPU, the amount of memory taken by them is the same as the file size of the DDS file itself. Usually, for 2D games the compression-based performance loss is not necessarily noticeable. For PNG files used on the DirectX stack, resources are allocated to decompress the texture. Not so for DDS files.
Depending on the case, DDS files can be generated on the fly. FallFury preserves relatively small textures in DDS format and larger ones, such as backgrounds, in PNG. It’s the best of both worlds. DDS files can be generated by a tool bundled with the DirectX SDK called dxtex (usually located in C:\Program Files (x86)\Microsoft DirectX SDK (June 2010)\Utilities\bin\x64):
There is also texconv that allows you to create DDS components from the command line, but we’ll explore that later in the series.
All DDS assets are located in the DDS folder in the solution. All that’s there are assets related to levels, such as obstacles, and assets related to character behavior, such as bear states and used weapons and powerups.
Unlike graphic assets that can be mocked from the very start, audio assets are a bit harder to come up with, mainly because at that point you need to be sure what the game will be like at the end. Music and effects should go together with the overall game feel. There are two types of audio components in FallFury—the music and the action-based sound effects. Music is played constantly, whether in the game or on a game screen such as the main menu, unless disabled by the user.
The way the audio engine works in FallFury, files are handled differently depending on where in the game they are used. All music is stored in MP3 files and the short sound effects are stored in uncompressed WAV files.
As a part of the new project that you are creating, replicate the folder structure for the Assets and DDS folders and add them to the solution. The way C++ project references work, you might want to switch to the “Show All Files” mode in the Solution Explorer:
Then, simply copy the folders to the solution folder itself. That way you will have all these resources as a part of the project itself and not just links to external files.
It’s a really good idea to use source control. There are multiple options available at no cost, such as CodePlex, Assembla, and Team Foundation Service. You need source control for multiple reasons. The most important reason of them all, however, is that code will break. There were multiple situations where I changed parts of the project and all of a sudden some components stopped working. With the project hooked to a source control system, all I needed was to do a quick rollback to the previous check-in and I was good to go.
A good practice I learned from Clint Rutkas is performing atomic check-ins. When something goes wrong, it is much easier to go back to the check-in where only 20 or 30 code lines were modified from what is currently in the stack, compared to going back to the solution where you will be missing two or more entire source files.
As you are following this project creation from scratch, notice how the entire code base is modular and interchangeable. If I decide to create a new game screen, I can do so easily by inheriting from an existing base class that provides the basic harness. If I want to replace a character model, I can do so by modifying a single class without breaking the entire interaction model.
Prototyping is also a big part of FallFury and it is key that no time is wasted working on features that will have to be entirely replaced or re-written. A good example to this scenario happened just as I started writing the project code. I noticed that the Settings charm required some XAML work for secondary popups that extended from the OS-invoked layer. As I was working on a pure DirectX application, I had to create the XAML in code-behind and that was one of the experiences that could’ve been avoided in a hybrid application. During the prototyping stage it is easy to spot potential integration problems and later change parts of the project to work better together. It is much more complicated to replace project components when the core is wired-in than when you have small parts that independently show how a part of the game works.
As you are about to start writing large amounts of code, you are probably wondering whether actual hardware is needed to test the application. The way FallFury was designed, you will be able to run it on any Windows 8 compatible machine, whether a desktop computer or a tablet. If the game is being run on the desktop, I assume that you probably do not have access to an accelerometer or a touch display. If you are running the game on the tablet, you probably do not have a physical keyboard constantly attached to it. These facts ultimately affect how you experience the game itself. From a development perspective, it is important to have multiple types of target hardware available, because the game might behave differently depending on the device configuration. But it is not required to follow this article series. As long as you have a Windows 8 machine, you are good to go.
Now onto 11 more articles on how to build Fall Fury!
For a complete, offline version of this series, you may download a nicely formatted PDF of all the articles!