One of Microsoft’s most successful products in the past years has been the Xbox and Xbox 360. In the more recent years Microsoft has given us developers the chance to add our own creations to the 360 Indie Arcade with their powerful XNA framework. Using XNA, you can go from concept to finished game in literally days, and with a few more hours you can have it deployed to Indie Arcade. This is why SOTC has decided to tackle some of the concepts behind XNA, starting with the Content Pipeline.
For our first foray into the XNA content pipeline, we are going to go over the basics of what, why, and how for this pipeline thing. It can be a little bit confusing for the novice XNA developer, but once you learn about it, it becomes much easier to understand and use. So enough chit-chat, on to the Content Pipeline.
What?
In the simplest of terms, the content pipeline loads and manges the content for your game, which could be anything from a level file to a fully animated character model. The pipeline framework itself is quite complicated, but basically it helps you get your content loaded in the most efficient way possible, then gives you the tools to use and modify that content at run-time. When you are using XNA, you can load and manage content without actually using the content pipeline, but that would be severely inadvisable considering our good friends at Microsoft already provide us with the best solution.
Why?
Well, there are a whole lot of reasons why you would use the content pipeline. First off, according to Microsoft’s documentation on the subject: “The chief reason XNA Game Studio uses a Content Pipeline is to help your game run fast.” This is due to the fact that all the game assets are converted to a binary format, then stuffed inside the executable, making loading much faster. On the performance side of things, the content pipeline definitely helps.
Another thing about the content pipeline that I love is its flexibility and extensibility. While you are given a few basic importers (such as bitmap or x files) to work with by default, but lets face facts, any self respecting game project will have custom content types. I know on several occasions I have used custom level file formats. But with the content pipeline framework in your hands, you can easily create the custom handlers that allow you to use the content pipeline to do the work for you. As noted above, this gives you the best performance possible, and also cuts down the overall code you need in your game project.
Speaking of cutting code, that is definitely another reason to use the content pipeline.The code that you have to write it drastically reduced when you use the content pipeline, because most of the code has already been implemented for you. When coupled with Visual Studio, XNA allows you to literally add a file to your project and load it for use in code with just one line. While it may seem a little confusing, that one line of code, it is still quicker than the four or five lines needed to load such content in with straight C# code.
To Convert an image to and from a byte array in C# .NET:
MemoryStream mStream = new MemoryStream();
bmp.Save(mstream, ImageFormat.Jpeg);
byte[] bytes = new byte[mstream.Length];
mstream.Read(bytes, 0, (int)mstream.Length);
Loading an image asset in XNA (which is in binary form already):
spriteTexture = content.Load<Texture2D>("MyTexture");
To me, it is better to use this one line, especially when you consider the content pipeline is there and works, so you don’t have to worry much about things going wrong. It is cleaner, and a lot easier to understand what is going on when you have XNA doing some of the grunt work for you. We also must remember that XNA does some of this work when you compile your project, not at run-time, so it only decreases the amount of code you need even more so.
It is pretty apparent that there are many reasons to use the content pipeline. Between the faster load times and the flexibility alone, you know you want to use the content pipeline. However, the next question on all of our minds is how exactly this miracle manager works…
How?
Now we come to the confusing part of the content pipeline, how it works. It is not so straight forward, but once you throw together a few diagrams, it becomes a bit easier to understand. Lets start with the process your content takes when you build your project.
One of the reasons the content pipeline is so efficient is because your content is converted to a special file type called an XNB file when you compile your project. These XNB files have no type associated with them, and are completely binary, which makes loading a lot faster. It starts this conversion process by using an Importer to parse the file into an object. Once the asset has been “Imported”, it is passed off to a content Processor which takes the imported data and compiles it into a binary format. The final step is to take this binary data and write it out to the XNB file, and you guessed it, that is the job of the content Writer. Between these three, your asset will go from a bitmap file to a binary XNB file in no time flat.
So, the content pipeline compiles our assets into these magical XNB files, which allows our content to be loaded lightning fast. Since this happens when we build the project, it saves a lot of processing during run-time as well, but what happens during run-time? Well, there is only one really important part of the run-time loading process, the content reader. What this reader does is it takes the XNB file and parses it into an object to use in your game code. It is the only component used during run-time, which adds to the code minimization.
The best part about this is that any of these steps can be overridden and customized to fit your needs. You can write custom imports, processors, writers, and readers that parse your assets through the content pipeline, but load the data in the way you want. Essentially, you could write your own data types for the pipeline to handle.
So now you know what the content pipeline is, and why to use it. We also went over how it works, and the basic steps XNA takes to load and manage your assets. Its a lot to take in on a purely knowledge standpoint, but once your start digging it, it gets a lot simpler. This is it for this installment into the content pipeline, but keep an eye out for the next one, because we will be going over what it will all look like in your code. Just remember, when you need coding help, all you have to do is Switch On The Code.