Posts Tagged ‘XNA’

My Experience Converting from XNA Game Studio 3.1 to 4.0

Sunday, October 31st, 2010

Microsoft released a big update to XNA Game Studio with version 4.0. The main improvement is Windows Phone 7 support. I will probably not develop for WP7 (see reasons below) but I still need to upgrade my current Xbox 360 project from XNA 3.1 to 4.0.

The process was not as smooth as I though it would be, so I wrote this article to help people transitionning from 3.1 to 4.0.

Upgrading to XNA 4.0

To install Game Studio 4.0, you normally need Windows Vista or Windows 7. However, Microsoft made a version for Windows XP working only for Windows and X360 projects. I don’t want to buy a new OS, therefore I am going with this “light” version. However, this version does not support Windows Phone 7. That’s a shame as I’d be interested to try things with a touch screen but upgrading to Windows 7 is expensive.
To install GS 4.0, you need Visual C# 2010 Express, and to get Visual C# 2010 Express on XP, you need the Service Pack 3. Problem: SP3 install failed for some strange reason. I could find this article on Microsoft’s site: When you try to install Windows XP Service Pack, you receive the error message “Access is denied” and the third solution consisting in running command line utilities solved my problem. I was not really sure what I was doing, but it finally worked :)

Converting the Project

When opening a GS3.1 project with Visual C# 2010, it automatically tries to convert it to GS4.0. Each project of the solution is converted. Of course, if you are using a compiled library (dll), you need to get or compile a 4.0 version. I had to re-compile Box2D.XNA and download the latest version of TiledLib’s dlls.

However, I had a problem when compiling for the first time, with the following error: “The referenced assembly “Microsoft.Xna.Framework.Content.Pipeline, Version=4.0.0.0, Culture=neutral, PublicKeyToken=842cf8be1de50553″ could not be resolved because it has a dependency on “Microsoft.Build.Utilities.v4.0, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a” which is not in the currently targeted framework “.NETFramework,Version=v4.0,Profile=Client”. Please remove references to assemblies not in the targeted framework or consider retargeting your project.”
Luckily, one guy had the same problem on Creators Club forums and the solution given by Stephen Styrchak solved my problem. It should be solved by changing the Target Framework in the application properties, but the option is greyed out. I had to edit my csproj manually with a text editor.

API changes

Ok, this is where the conversion really starts: fixing compiling errors due to numerous API changes in the framework. Here is a list of the main changes that affected my project:

Color struct: The Color struct has moved to XNA.Framework (from Xna.Framework.Graphics). A few constructors have also been removed, such as this one: Color( Color, float). I used it a lot. Easy to fix but Color is widely used in my project so that involved many changes.

Vertex buffers and Effects: There has been a few changes with vertex buffers and effects. There are many portions of code to update because of that but the new API is really simpler and better. For instance, you do not have to do Begin/End on effects and each pass, but you just use Pass.Apply: Less code to write for the same result. Also, when you have standard vertex types, you do not need to use VertexDeclarations. The GraphicsDevice.VertexDeclaration member has been removed. Again, less code to write!

Pixel/Vertex Shader compiler : I found the compiler more strict. For instance, I had a texture and a technique with the same name, it did compile with GS 3.1, but not with GS 4.0. I also had a pixel shader function called PixelShader and it does not compile on GS 4.0.

Point Sprites: They simply have been removed. I don’t use them in my current project, but my last game Spring Up Harmony used point sprites for the back ground effect. It takes some time to update to triangles.

Render Targets: In addition to a few simple API changes when setting render targets, the most notable change is the removal of the ResolveTexture2D class. You now need to use a RenderTarget2D and can’t directly get a texture from the backbuffer.

Storage changes: A few API changes have been made in the storage too. Biggest change is the OpenContainer method that is now asynchronous (Begin/EndOpenContainer). A few functions have been renamed too.

Executing of the Game

Ok, now that the game compiles, let’s run it! And another problem occured here: The game does not run at all and asks for a DX 10 graphics card. Easy to fix: modify the XNA project properties and choose “Reach” instead of “HiDef”. Difference is that Reach has a limited API for WP7 but should be enough for me.

References

Here is a list of resources/blogs that I found very useful while converting my game to GS 4.0. You should read them all ;)

MSDN Page: What’s new in XNA Game Studio 4.0

Shawn Hargreaves’ blog: articles on Vertex BuffersEffects, removal of point sprites, render targets.

Nick Gravelyn’s blog: article on storage in GS4.0

Done

And voilà! Conversion is done and the game runs properly (I did not test thoroughly yet). I was worried the new default use of premultiplied alpha would cause problem but I haven’t found any. If you had a problem converting your project that is not mentioned here, feel free to comment!

3 Simple Tips to Avoid Memory Allocations with XNA/C#

Friday, May 21st, 2010

Long time without posting. I’ve spent a lot of time working on the game, contracting art, buying sound effect and music assets, designing the levels… New screenshots/video should come very soon.

Anyway, back on topic: when developing from C++ to C#, I found out very strange that you can allocate memory but you cannot free it and have to let the garbage collector do it. But I finally got quickly used to it and found it quite handy… Until I found out that garbage collection is not free and usually causes framerate drops, especially on X360.

clrprof

Using the CLR Profiler (screenshot above), you can easily see where you are wasting memory (well, it can be scary the first time you see it but in fact, it’s easy). I nearly removed all my runtime allocations with this tool, here are the few tips that can be useful:

1. Be careful with the class string

String is allocating memory every time it returns a new string. StringBuilder is the key to the problem. I didn’t even know what StringBuilder was before working on memory and now I use it everywhere I need to take care about memory. There are some awesome tips (and source code) about StringBuilder on Gavin Pugh’ blog. Especially this and this. You have everything you need now :)

2. Reuse your lists

I had multiple sections of code creating a temporary List<> in order to add elements to need a special treatment. This was in an update function in my case. It is handy and fast to write code like that, but it allocates memory. To fix this, I know have the List<> as a member of the class. I clear it and reuse it when needed. When creating a list, you should use the constructor with an int used to define the default capacity of the list. (List<Vector2> l = new List<Vector2>(64) for instance).

3. foreach loops

I converted my foreach loops in C++ like for loops and it saved me some allocations. Memory allocated due to foreach loops on lists is showing up in the CLR Profiler as System.Collections.Generic.List<T>.

Conclusion

I hope you’ll find this useful. In Spring Up Harmony, I still have some run-time allocations, mostly in the particle engine, when a new fx is launched (I use Mercury for now). However, it seems that the garbage collector is not causing hick-ups therefore I’m ok with it.

Yes, multi-threading in XNA/C# can be that simple!

Wednesday, April 14th, 2010

Multi-threading is often causing problems for multiple reasons: synchronization, deadlocks, concurrent access to memory… But with my recent experience with multi-threading in XNA/C#, you can really do simple and efficient optimizations.

While looking for possible performance improvements in Spring Up Harmony for Xbox 360 (PC), I have seen a simple situation really suited for multi-threading. You can see that situation with the following screenshot of my in-game profiler (click to enlarge):
Frozax-4
I have two tasks with performance issues since I started to run the game on Xbox 360 : the dynamics of the background effect and the computation of the estimation of the launch of the ball (running a simplified physics simulation multiple times, through Box2D.XNA). On this screenshot, these tasks are called VelGrid.U(9) and Launchers.U(14). The first part of VelGrid.U (Comp.Balls,10) uses the data of the physics simulation but DynaColLines(11) doesn’t. Therefore, the VelGrid.DynaColLines and Launchers.U are totally independent with each others. No data is shared between these code sections. Perfect candidates for my initiation to multi-threading in XNA! :)

The e-book found here (recommended in multiple threading articles) is really awesome and helped me find the algorithm I need to use. I want to start the Launchers.U at the same time than VelGrid.DynaColLines and wait until both are finished. I know this is not optimal, but it allows me to simplify the problem and avoid so many threading pitfalls.

I just have to use two AutoResetEvents. The Launchers.U section is created in a thread and waits for a “Go” signal from VelGrid. After doing its job, it sets a Ready signal so that VelGrid knows when to carry on after doing its own stuff. Two different cases can happen, depending on which section finishes before the other.

Here are screenshots of the in-game profiler showing the differences (taken on X360). Every code section prefixed by a * means it’s executed on the thread.

Case 1 : The code on the main thread completed before the code on the worker thread:

thread_slower
The Velgrid section has to wait for the Launchers to complete, shown with the red arrow.

Case 2 : the code on the main thread completed after the code on the worker thread:

thread_faster

The thread is idle while the main thread still works (red arrow).

With this simple threading mechanism (coded and tested in a few hours only), I have been able to optimize the game. In the basic test level shown here, instead of 2.3 + 3.1 = 5.4 milliseconds spent on the main thread for both features, the game now spends 3.6 milliseconds, running two threads at the same time (33% gain). In this test scene, the Velgrid.DynaColLines is “free”.

Since I took these screenshots, I have made a few more changes : now, the whole Box2D update used while the game is in motion is threaded too.

Last important thing to know, on Xbox 360, you must choose which core to use for your thread. Just read the msdn page about the SetProcessorAffinity, everything you need to know is here. You can see in this article that I still have a few cores available :)

In conclusion, if you have independent sections of code that take some time to run, you can improve that very quickly using this method.

On-screen profiling for XNA

Wednesday, April 7th, 2010

A few days ago, I read an article called Among Friends: How Naughty Dog Built Uncharted 2. The interesting screenshots on the third page gave me the urge to create what I call an “on-screen profiling” tool for Spring Up XNA. I talked before about profilers and how to use them to find which sections of your code need to be optimized. But a visual tool is really handy, because it’s real time, and with Edit and Continue on PC, you can even see your improvements live!

So, I spend some time working on it, and here is a sample screenshot (click to enlarge):

onscreen_profiling_sample_x360The bars show the timeline of the current frame. In the bars, there is the name of the section. For clarity, all profiled sections are also displayed in plain text with the following informations: Name, Time elapsed this frame (in millisecond), smooth time elapsed, percentage of the 60 fps frame (16.6 ms). The vertical magenta line is the limit of the 60 fps frame. On this screenshot, my objective of 60 fps is not met, there are some bars displayed after it :)

I am really happy with the results, you instantly see where optimization is needed and you also see the results quickly. For instance, after seeing the previous screenshot, I concentrated on the “Velgrid.D” section (section drawing the background effect that is seen in motion here). After some improvement, it still was not fast enough. I noticed that the problem was simply the overhead of calling SpriteBatch.Draw more than 5000 times. I therefore decided to write my own vertex+pixel shaders and you can see the result here:

onscreen_profiling_final_x360It’s now so fast that we can’t even see the name of the section in the bars and I have to have a look at the list to see the exact time taken by this section of the game (number 15).

The profiling works obviously on both Xbox 360 and PC so I could compare both hardware. As I could read here and there, the X360 build is much slower than the Windows one. I made two screenshots of the same scene with a scale of the bars so that the length in pixels of the full frame is around the same on each platform. Here is the screenshot of the windows build that you can compare to the first screenshot of this post: 
onscreen_profiling_pc_scaled

The “slower” sections are not the same. Globally, the X360 is better at using its GPU and the PC using its CPU. Of course, this is heavily dependant on the PC platform. For information, I am using a 3.4 GHz computer with a X850 graphics card.

And just for fun :) , the first screenshot of the profiler on X360, before I started any optimizations:

onscreen_profiling_first version x360The frame took 165% of my objective target frame (60 fps). I can’t even see it all on screen. I am now at 75% of the frame, and with an additional feature (glow around objects, section 9 on the second screenshot).

So the small amount time taken to make this in-game tool is very well spent. It’s obviously quicker than running a profiler and waiting for the results, even if it’s not as precise. And the great thing is that this was easy and interesting to program :)

First Run on Xbox 360 : Problems and Solutions

Friday, April 2nd, 2010

I decided about a month ago to start working on the Xbox 360 version of Spring Up in April. I think it can be interesting to share my experience about that.

Part 1 : XNA Creator Membership

Basically, you just need to pay creator membership (99 € for one year in Europe), launch XNA Game Studio Connect on your console and that’s it.

Problem 1 : You have problems to redeem your XNA account to a new X360 profile?

Solution 1 : Do not mix up your forum name and GamerTag. Yes, this one was easy but it took me at least 30 minutes to find out what was happening. :)

Problem 2 : XNA Game Studio Connect does not recognize your account as premium when you launch it even though you paid for membership?

Solution 2 : You have to wait for some time (a few hours, maybe half a day) and everything will be fine. Quite frustrating, I know.

Part 2 : Compiling your game for Xbox 360

Microsoft made something simple : just right click on your project in Visual C# and choose “Create copy of Project for Xbox 360″. I took my main project and all the dependencies were converted too.

Problem 3 : You have very strange compiling errors? When converting Box2D.XNA, I had weird errors such as “Class C does not implement inherited abstract member M” AND “no suitable method found to override M”.

Solution 3 : Make sure you use the proper version of assemblies. I don’t know why but the converter put assemblies of XNA 3.0 instead of 3.1. Using 3.1 assemblies fixed my problem.

Problem 4 : The code does not compile but it works fine on Windows?

Solution 4 : Make sure you do not use windows specific code. You will be able to see warning icons if you have invalid assemblies in your Xbox 360 projects. If you want to keep windows specific code, just use #if WINDOWS / #endif so that it compiles properly on Xbox 360. In my case, my level and dialog box editors are only available on windows because it needs to create XML files.

Problem 5 : You can’t build your XNB data from XML using your own classes?

Solution 5 : Make sure the Content projects still have references to windows builds. Resources are built on the development computer, using the windows assemblies.

Part 3 : Running the Game on Xbox 360

Problem 6 : Code 3 Error?

Solution 6 : When you have Code X errors, it is because the console hangs without being able to break or throw an exception to the debugger. To track this problem, I simply traced the code I suspected. As the problem happened on a specific action, I could easily see where was the problem. My problem was just a null pointer access that happens only when there is no savegame. I always have a savegame on PC, so I did not see the problem before. The strange fact is that when I traced the code the second time, I properly had the NullPointerException.

Problem 7 : Your game is slow?

Solution 7 : I knew Xbox 360’s are usually slower than PCx with XNA but I was still very surprised my I ran my game for the first time. I immediatly launched a release build to try to reassure myselft but it’s still quite slow. I am not sure what is the problem for now so I will improve my profiling code to see which GameComponent is the problem.

Conclusion

That’s it for my first run on X360. I hoped this helped some of you!

Measuring game performance : framerate is not everything

Thursday, March 11th, 2010

I am currently having a few problems with performance in Spring Up XNA. I have two features that are too expensive in processing power : the background effect and the computation of the preview trajectory of the ball.

I know these features are not usable at this cost because as soon as I activate one of them, my framerate drops and the game does not run at 60 FPS. When your game runs at 60 FPS, everything’s fine. When it does not, how can you tell how “far” you are from it. And because XNA is trying to catch up when your game is slow, this is even more obscure (there is a very good article on Shawn Hargreaves Blog about this topic called Understanding GameTime).

fpsTherefore, in order to have accurate and useful performance information in real-time , I am displaying on screen the time spent to compute and draw the last frame, in milliseconds.

This is done easily using the Stopwatch class. This class is standard C# system library, it is not part of XNA. It is very easy to use:

stopwatch.Reset();
stopwatch.Start();
// Code to time here
stopwatch.Stop();

You just have to time the whole Update and Draw functions. Then you can read the number of milliseconds directly in the ElapsedMilliseconds member of Stopwatch. However, as this value is a long type, I prefer to compute the number of millisecond more precisely using this code:

(float)StopwatchUpdate.ElapsedTicks/(float)Stopwatch.Frequency*1000.0f

And to display it properly, I use the following formatting:

string fps = string.Format( "fps:   {0:00.0}\nupdate:{1,4:00.0}\n
draw:  {2,4:00.0}", _fps,
(float)StopwatchUpdate.ElapsedTicks/(float)Stopwatch.Frequency*1000.0f,
(float)StopwatchDraw.ElapsedTicks/(float)Stopwatch.Frequency*1000.0f );

I first thought that the numbers would change so quickly that it would not be usable but it’s pretty constant in my game. I can see huge differences when disabling some GameComponents. It is also useful to see if you spend more time in the update part or the draw part. You must have separated game logic and rendering properly, of course.

I told before in this blog that you must not spend time optimizing when you do not need too. But having this few lines of code is harmless and can be useful while adding new features:

  • If you see that you spend 5 more milliseconds in this session than in your previous one, you may need to have a closer look at this new code.
  • As Spring Up XNA is heavily using dynamics (through BOX2D), I can also compare the performance of the different levels.
  • You can see when a single frame takes much longer to update/draw (choppy framerate).

Hope this helps!

Video : Dynamic level demo and background effect update

Tuesday, February 23rd, 2010

The development of Spring Up XNA has been going pretty well last week.

Here is a new video, please note that it is still not the final art, just placeholders for now :

You can see the following:

  • New ways of using the physics engine in the levels (joints, gravity…)
  • Small improvements on the background : slight halo around targets, bloom reacting to matches, especially when hitting sparkling balls (the sparkling balls are part of a modification of gameplay from Spring Up PC/Mac. I will talk about it later. This is also the reason I cropped the borders of the video ;) ).
  • New particle effects (code in place, art also not final)

These days, I also implemented the sound effects (I just recoded the wavs available in the original version), improved the level editor, added many types of objects (bumpers, shrinkable balls, motors, splines…), added player score with statistics…

Globally, it’s going well, but I am having difficulties in level design. I find it very hard to innovate in each level but I still have a few interesting level prototypes in place.

Hope you like it!

Box2D.XNA : a great 2D physics engine

Friday, February 5th, 2010

Box2D is a 2D physics engine created by Erin Catto. On Win/Mac, I used a very early version of Box2D (it was released nearly two years ago!). I just made a few specific changes for the game. Of course, as I told in a previous article, XNA games must be made in C# and Box2D is made in C++. I could find multiple open-source projects of ports of Box2D in C#. They are based on the last version of the C++ engine and a lot of changes occured since I developed Spring Up!.  It means that to use a C# port, I have to adapt a lot of my physics code. But this is a good thing for the following reasons:

  • I will have the new version of the engine : there are probably some debug and optimisations.
  • New features : can be used to improve the game
  • Lots of C# code already written, I won’t have to port it myself.

Among the two or three C# ports available, I decided to go with Box2D.XNA. This port is written by Brandon and Nathan Furtwangler and they are doing a very good job! They are very active: when I fixed them a bug, they put it back in the code base in less than a day and they port the changes of the C++ version very quickly.
Compared to the old C++ engine I was using previously, the new version has been greatly improved, here are some examples:

  • Dynamic/Static/Kinetic types are included on bodies, no need to play with infinite mass directly.
  • Collision filtering is now included in the API. I developed my own system in Spring Up! but throw it away in C#.
  • Motors are included. I also developed basic motors myself in C++.
  • More joints types: only one type was available.
  • Collision detection includes polygons, not just only circles and rectangles.

As I’m still working with the level editor, I started to include new features in Spring Up! Here is a simple video showing a new possibility made with Box2D.XNA (showing motors, complex shapes, joints and collision detection).

As you can see, the gameplay does not seem that interesting in this sample but it’s just made to test the dynamics for now. I will concentrate on level design later and I am sure I will face a lot of difficulties.

In conclusion, if you need 2D physics in your game, use Box2D, and if it’s for XNA, use the Box2D.XNA port!

Spring Up! XNA : first try at background effects

Wednesday, January 20th, 2010

I spend some time trying to create an interesting visual effect in the background of Spring Up! XNA. The backgrounds of the PC/Mac versions are not really nice. I tried to do something more abstract and animated depending on the flow of the game. Geometry Wars 1 and 2 did a very good job at that. While trying to develop an effect, I came up with many different results. I uploaded a video of one of this effect (you can see it in full res here).

Of course, feedback is very much welcomed (negative, positive, ideas…).
I personally have some concerns about a few things:

  • Black background, is it too simple?
  • When background is colorful, I think the player might not see the “real game” because it attracts the eye.
  • Colors are a bit too much “programmer art”. I made also some black and white tries that were nice too.

I have many variables available to tune this effect and each one of them really changes the final result. Basically, the algorithm here is a grid of particles that are animated and lit depending on the velocity and position of the moving elements around them.

I will also probably add thin trails behind objects. For boxes, I will try to attach multiple trails to  every corner.

I also have a bloom effect I did for fun before starting this project, I might try to add it in Spring Up!, probably on the trails, maybe on the background too.

Win/Mac and X360 differences (3) : XNA Content Pipeline

Wednesday, January 13th, 2010

In this post, I’ll talk about the XNA Content Pipeline. When I first tried to load a resource in the XNA game, I was trying to do as usual : opening a file and reading it using standard file reading functions. However, on XNA you have to use the Content Pipeline provided and to be honest, they have made a very good work with that. This pipeline can load some known file formats (jpg textures or wav sounds for instance) but you can extend the pipeline for your own custom formats.

I used many different types of file format for Spring Up!, for instance:

  • TGA for 32b images (I used TGA because it’s a very simple file format)
  • SWF for menus, level description and physics definition (ShockWave Flash, using the gameswf library)
  • WAV for sounds
  • OGG for music
  • Custom text files for translated texts and particle definition (called RSC and PRT)
  • Custom binary files for various data (DAT files).

The XNA Content Pipeline is really integrated into your XNA game project. You just add the resource to your project and when you compile it, the data is imported and converted in a XNB (XNA Binary File) using a Content Importer. This XNB file is generated for the right platform. It means you do not have to bother about little/big endian of the platform (Windows or X360). Once the resource is in your project, you create game objects with only one line of code. For instance, you can add a texture file to your project, and then load it using the following code:

Texture2D my_texture = Content.Load<Texture2D>("texture");

There are many file formats handled by XNA but when using specific data, you have to develop your own custom Content Importer. As told in a previous article, I will not port gameswf for many reasons so all the data I have in SWF files has to be included in another way into the X360 game. I started to include one of the most important data : the definitions of the levels. To do this on X360, I developed a quick XML exporter in the PC version of Spring Up! Then, I read the XML with my custom Content Importer. The XNA Game Studio then generates the XNB. The following diagram shows the flow of the data:

Data flow for levels data in Spring Up!
Levels data flow in Spring Up!

Now that my importer is in place, I can read a level definition using the following code:

LevelDef level = Content.Load<LevelDef>("level01");

And that’s it!

I have three importers already in place in the current version:

  • Sprite : binary format containing position and size of a sprite in a texture page. It was my first importer using XNA. It could (should?) have been XML. Original PC data was in the SWF, it is exported in binary from the PC game.
  • Level : position and type of items of the levels of the game. Original PC data was in the SWF, it is exported in xml from the PC game.
  • Physics : the definition of the physics properties of the items (size, shape, mass). This one is not completed yet, I still have pivots and joints to include. Original PC data was in the SWF (in actionscript code), it is exported in XML from the PC game, too.

If I knew from the beginning that the game would be developed on XNA, I would have done differently. The fact that I’m porting an existing product made me choose this solution of creating the exporters on PC and reimporting the data in XNA Game Studio. Ideally; I would have createed a level editor (with a Windows XNA project probably) saving data in XML. Then I’d use the content importer to put the resource in the XNA game and read directly the XML for a PC/Mac game (see diagram below).

Possibility for a multiplatform project
Possibility for a multi-platform PC/Mac/X360 project

As I plan to improve greatly the game, it is still possible that I will develop a specific level editor to be able to create new types of objects and physics items.

That’s it for my basic introduction to the XNA Content Pipeline. If you have any questions about the use of the pipeline, about importers or anything else, feel free to ask in the comments section below!