Measuring game performance : framerate is not everything

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).

Therefore, 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

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!

NProf : A Simple, Efficient and Free XNA Profiler

On its google code page, NProf is described as a statistical profiler for .NET applications. Good news: XNA being .NET, it can be used to profile games.

It’s well known that in order to optimize, you first need to find what part of your code is slow. That’s where a profiler comes handy, it finds the bottlenecks of your game and then you can optimize what needs to be.

The title of the post says it all, NProf is trivial to use, efficient and free. Once you download it, you select your XNA game executable, play it for some time and that’s it! I spent some time trying to find great profilers when I developed for PC and Mac but could not find anything really usable and affordable. I finally timed critical code sections with custom code and studied the log manually. Fortunately, NProf does all that for me in XNA.

I had a few surprises when I ran NProf. For instance, yesterday I could see that 21% of the game was spent in one method:
Color.Color( Vector3 )

This XNA constructor converts a Vector3 in a Color and it is called a lot in my game to create my background effect (see an old version in motion here). In this constructor, the expensive call is PackUtils.ClampAndRound. I do not have access to this code, but I can use another basic constructor and do the conversion myself. Here is what I ended up doing:

Color col = new Color( vColor +
    new Vector3( start_val, start_val, start_val ) );

int r = (int)(( vColor.X + start_val) * 255 );
int g = (int)(( vColor.Y + start_val) * 255 );
int b = (int)(( vColor.Z + start_val) * 255 );
Color col = new Color( ( r > 255 ) ? (byte)255 : (byte)r,
    ( g > 255 ) ? (byte)255 : (byte)g,
    ( b > 255 ) ? (byte)255 : (byte)b );

The new code doesn’t clamp values below zero but I don’t need that feature. The really important thing is that it is now more than 12 times faster than before!

Without NProf, I would not have guessed that this constructor was that critical.

The main problem I see with NProf is that it only profiles your game on Windows and bottlenecks may be different on the X360.

Anyway, I really advise you to run your game in this profiler before you optimise anything. Be sure to use a release build.

Feel free to share your experiences with NProf!

Box2D.XNA : a great 2D physics engine

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!

Video : Level Editor

I am mostly working on the level editor. I was not sure when I started this project that I would need a specific level editor. But Spring Up! X360 needs some serious changes in the level design to improve the quality and to adapt to the X360 platform, therefore I need this new level editor. Working on tools with C# is great : it’s really powerful and efficient! Technically speaking, the level editor is just a Game Component (DrawableGameComponent XNA class) of the Game. When the “Editor” component is created, all the new mouse and keyboard shortcuts are available.

As you can see in the video, here are some features implemented: create, move, rotate and delete items and targets. You can set up objects as static, dynamic or with a motor. There is also a snap feature. And as the game is running at the same time, you can play directly in the editor.

You can also see some of the new shapes that will be available in Spring Up! XNA : a triangle and pentagon.

That’s it for today, I hope you liked it!

Spring Up! XNA : first try at background effects

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

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:

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).

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!

Price drops : better late than never!

I probably should have done this a long time ago, but I finally changed the prices of my games to adapt to current market. Here are the old and new prices:

Spring Up!	Around the World	Shapy Deluxe
$19.99 $ 6.99	$19.95 $ 6.99	$9.95 $ 1.99

Recently, many big companies involved in casual and downladable games business had big price cuts:

• XBL Indie Games prices changed a few months ago and are now available at either 80, 240 or 400 MSPoints ($1, $3 and $5 dollars).
• Big Fish Games games are now available at $6.99. Before, this price was reserved to Big Fish Game Club. Club games now sell at $2.99.
• Reflexive games have multiple prices, apparently from $2.99 to $10.99.
• Some Steam products are sold from $2.
• iPhone games are also very cheap ($1 – $5 usually).

Developers have different thoughts about cutting the prices. I honestly do not know if it’s efficient or not, but there is one observation I’ve been able to make: I am selling games from Big Fish using their affiliation program on frozax.com. When Big Fish Games changed their prices, I didn’t notice any change of income, or maybe a slight increase in profit. I do not have the full details of the number of games sold, but as the income per month stayed about the same, I can suppose there are more games sold to compensate.

Let’s hope I can increase my volume of sales, too. I’ve had nearly no sales in the last few months and a few sales could help!

Win/Mac and X360 differences (2) : Screen resolution and aspect ratio

The second “Win/Mac and X360 differences” post is about the aspect ratio and resolutions of the screen. This may not apply to all games as more and more casual games nowadays can be played on multiple resolutions included the X360 ones. However, I decided to write a post about it because that’s a problem I am facing at the moment.

Most PC/Mac casual games are only developed for a 4:3 resolution (640×480, 800×600 or 1024×768 generally). However, on X360, resolutions are mostly 16:9. In fact, the 1280×720 resolution is recommended by the XNA developers to ensure the game works on every video adapters. Spring Up’s resolution on computers is 800×600, and it will be 1280×720 on XNA, as shown on the first screenshot revealed last month.

Of course, there is a difference in the number of pixels, but the biggest problem is the aspect ratio (from 4:3 to 16:9). The following picture illustrates the problem.

The blue sections represent the X360 screens and the green sections represent the PC screens. The first illustration shows how the 800×600 screen fits in the 1280×720 screen without any change of resolution. That’s the easiest way to do and what I did for the first screenshot of the game. Basically, you don’t change anything, you just render your game in the center of the X360 screen.

On the second illustration, the PC screen is enlarged so that it fits with the height of the X360 one. This is a 1.2 scale that transforms the PC screen in 960×720. You can see there are blue portions on the sides. That’s what Peggle did (see XBLA screenshot). They just added some (useless?) stuff on the sides to fill the gaps.

There is a third solution that scales the PC screen so that the left/right borders match with the 1280 width of X360. This is a 1.6 scale. In this case, some pixels are lost on the top and bottom if you keep the 4:3 aspect ratio.

I do not want to scale the objects of the game (balls, fans, launcher…) because I prefer pixel perfect sprites (one pixel of the texture is exactly one pixel on the screen). Consequently, in Spring Up!, I will probably move the items that compose the levels so that I take up more space on the screen. A good point to this solution is that it will contribute to correct one problem of the game stated earlier: objects will less likely be stuck due to extra spacing between targets.
I will also tweak the level design to “fill the blanks”, mostly on the left and right sides.
As the background is made up of tiles of 100×100 pixels, I just have to draw more tiles so that’s not a problem.
The walls will of course need to be moved to the sides of the screen.

Another detail that sometimes bother people that don’t think about it right from the beginning is the “title safe frame”. On X360, it is required that every important instruction on screen is displayed in the inner 80% of the screen. In 1280×720, that is 1024×576. On Win/Mac, I have many important information on the borders of the screen (bonus bar, score, level). I will need to change game design here to pass this requirement. I keep that in a corner of my head for the moment and will decide how to do it when working on the UI.

That’s it for resolution and aspect ratio, feel free to comment!

And happy new year!

Win/Mac and X360 differences (1) : C++ and C#

I will write a series of posts about the differences in developing for Windows (or Mac) and working for X360 with XNA Game Studio.

The first post of these series is about the most obvious difference : the programming language.

All my PC and Mac games were developed in C++ because that’s the language I’m most efficient with. I developed in C++ for years. Retail X360 games are mainly developed in C++ too, but to work with XNA Game Studio, you have to use C# and the XNA Framework. C# was new to me, but it’s easy to learn when you know other objects-oriented languages.

XNA Framework is also offering a lot of interesting libraries to help develop games. For instance, here are a few libraries I used on PC and Mac that are provided by the XNA Framework:

• 2D rendering : I used Popcap framework (Win) and SDL (Mac). XNA provides easy ways to draw sprites using the SpriteBatch class.
• Audio : I tried Audiere in my first Windows games and now I use SDL_Mixer (Win and Mac). XNA uses SoundEffect and Song classes.
• Game management : I used in-house code, XNA provides various helping classes (Game and GameComponent for instance).
• Math : I developed my own functions in C++, XNA has all you need (2D/3D Vectors, Matrices…).
• Input : I used specific Win32 and Mac functions in C++. Once again, XNA provides easy classes to deal with input (Keyboard, Mouse and GamePad classes). Of course, inputs are different on computers and X360 console. More on this later

But there is still many code to rewrite when porting the game. For Spring Up! there is obviously all the game code, and the physics engine. I am also using gameswf (a flash library) to draw all the UI of the game in Win/Mac. I won’t try to port it to X360 for two reasons : 1) it’s a lot of work, and 2) the UI I made with gameswf must be used with keyboard/mouse. I will probably have to write specific UI code for X360.

C++ code that is not platform specific (like game code or even the physics engine) is quite easy to port. Here are the few adaptations I have to make:

• No pointer in C# (well, except unsafe mode but I don’t use that). Basically, it just means removing *’s
• No delete. You have to trust the garbage collector. For now, it’s working smoothly but I’ve read some people are having troubles with that.
• No include files : that’s awesome! One file only per class is handy.
• No STL (even though I don’t use them much) : C# lists are very handy, better than STL and the syntax is also easier to read.

When I have big functions to port, I basically copy and paste the code from C++ to the C# editor, and modify what needs to be modified. Quick and easy. So far, it went pretty smoothly.

Feel free to comment!