Category Archives: Physics

An entity/component system’s attempt using Box2D

One year ago, I heard about the Entity/Component Model for the first time. It seemed to be awesome for game design / development. This is 3 links/resources for a good introduction : Gamasutra the Entity Component Model, Entity Systems are the future of MMOG development, Entity Systems. Then Richard Lord has made a very good blog post with code example using his own framework : Ash. And finally, Shaun Smith’s experience using Ash.

All the code example is available on the new Citrus Engine’s GitHub repository. Compile the src/entity/

During this year, entity/component system has always been something I wanted to try… but that was scary : this is not OOP, that’s a new way of programming. I wanted to add this system to the Citrus Engine as an option to handle complex object. For basic object OOP is great and easy to set up, but for complex game object which may have new abilities on the fly, you’ve quickly a Class with 700 lines of code and conditions. Not easy to maintain some weeks later. The Citrus Engine handles physics engine (Box2D & Nape) & a simple math-based collision-detection system. However it comes built-in with a “platformer” starter-kit based on Box2D, so I made my entity/component system’s experiments using Box2D. And that was not simple.

Continue reading An entity/component system’s attempt using Box2D

Citrus Engine on Nape and physics performance improvement

Hi folks! Since my studies are over and my new portfolio online, I have time to focus on personal projects. Yep, it was time to contribute again to the Citrus Engine. I’ve worked 3 days at full time focusing on its big issue : mobile performances. I’m glad to say that now they are just an old memories!

6 months ago, I’ve made the CE compatible with Stage3D thanks to Starling and added some cool stuff. CitrusEngineV3 BETA 1 has been downloaded 3047 in 6 months, that’s not bad! However it didn’t see lots of Stage3D game, because it was missing the point : people wants to make mobile games.

You will find all the sources at the end.

Continue reading Citrus Engine on Nape and physics performance improvement

Tribus, Graduation Project

On Wednesday 20 th, I made my last orals for school. Some weeks ago, I’ve finished my training at Swad‘s web agency in Annecy. Since Wednesday my sandwich course at Gobelins school (Annecy) is finished, and now I’m in “holiday”. It means that I’m working on my new Portfolio and looking for a job probably at Lyon, France 😉

Let me introduce Tribus, the first game which use bus public transportation as gamification!
We were 4 people behind this project, Pauline the Graphic Designer, Coraline the Designer, Lory the Project Manager / Developer and me as the lead Developer.
Tribus is based on a simple observation : public transportation are boring time for many people. The idea was to play in real time with the bus public transportation and break the boredom thanks to the Gamification.
The Tribus’ concept is to gamify the bus route using its own elements : location, speed, line, bus stop… and offer a game!

The concept was there, but what type of game offer? A real time massive multi-players space opera? Impossible for a small team in 4 – 6 months, we aren’t Electronic Arts. A survival game with zombies? I loved this idea, it could have been awesome if we have worked on subway : safe point, network lost… all the ingredients were already present. However we wanted a game for everyone : fun, easy to play, stress-free… yep, one more casual game.

Tribus is a Canabalt type of game, it is close to Jetpack Joyride. But how are bus elements injected in the gameplay?
It is very difficult to have information on the bus, bus’ companies don’t disclose these informations. So we used the smartphone’s GPS. Thanks to it we could know our position and so the bus one. We have located bus stop in a database and so we knew if a user follow the bus route and then suppose that he is using the bus! The GPS is also used to know the bus speed and thus change the speed of the game.

We developed for iPhone, using Chipmunk and Sparrow for the game (not the app interface) and made a simple port of the Citrus Engine. Since this is my first project using Objective-C the port is not very “user friendly” and it can be improved a lot. Anyway, that was a very rewarding experience.
All the source code is available on GitHub.

A short video :

Screenshots :

The Citrus Engine goes on Haxe NME, welcome to the CitruxEngine

One month ago I started to work on the CitruxEngine. I was very confident with Haxe performance on mobile and NME cross platform opportunities. And now, I can say those are awesome!

In April 14-15th, I was in Paris to assist to the Haxe conf 2012. It was really cool, Silex Labs has made a good job! Conferences were very interested and the community greatly friendly. And I had the opportunity to make a lightning talk concerning my contribution to the Citrus Engine 2D game framework and its port on Haxe NME. The presentation was a bit from scratch, but that was a good experience! I’m very happy to be the first to start the lightning talk, since there were very serious projects 😀

CitruxEngine Github.
CitruxEngine Demo. Simple demo which have been tested on Flash & CPP (using left/right key and spacebar) and iOS (touch & accelerometer). There are sound, animations (idle, walk and jump) and physics.
The port is currently not finished!

I will not present some code here. If you are already familiar with the Citrus Engine, there will be no problem. Take a look on the example on Github.

When I started the port, I would the CitruxEngine be as cross platform as possible. HTML5 is promising, and Niel Drummond the man behind Jeash has made an incredible job! However I found that the Haxe NME Box2D port has not very good performance with HTML5. So I’ve dropped the HTML5 target at the moment, but I keep an eye on Jeash!

Thanks to Haxe NME, Box2D runs very well on mobile! This is mostly the reason why I’ve started the CitruxEngine. The Citrus Engine uses the AS3 Alchemy version of Box2D which has some differences with the original. It seems there is a bug with the Haxe NME Box2D port : the beginContact & endContact listeners are fired all the time if a dynamic body is on a static body (like a hero on a platform), whereas it fires only once if there are 2 dynamics bodies. This behavior is blocking me.

I made my test with the spritesheet haxelib which uses SpriteLoq. At the moment it works well. I’ve not made serious test with animations.

Level Editor
I love how the Citrus Engine handles Flash Pro as a Level Editor. I would like the Haxe NME version handles it as well. But at the moment we can’t read AS3 code in a SWF file (it is the way that class and properties are defined), so I need to think to an external way. Maybe it’s time to reconsider the Level Architect!

The console is really a cool feature of the Citrus Engine, it will be available in the CitruxEngine too. I’ve started to implement it, but it’s not ready yet.

I will continue to work on the CitruxEngine, but now I’ve to focus on my school project using Objective-C, it’s really hard to get back when you have tested Haxe power ! In less than two months I will be graduate and looking for a job, future is exciting.

Thanks to postite & elsassph for their help!

From Box2D to Chipmunk

Hey there, I’ve been very busy this last weeks working hard on my 2nd school year project, a mobile game. In a few weeks, I will explain it, but for now let’s do some programming stuff!
The game is a side-scrolling 2D game. See Canabalt or Jetpack Joyride, they are great games!
Developing for iOS, I used Sparrow framework. It is awesome, and really easy to learn coming from AS3 & Starling.

Why did I develop in Objective-C since AIR 3.2 is out ? Refer to my previous post about my personal preference and the future of web development ; I decided to learn Objective-C and this project is really a good opportunity! I have followed the news about HTML5 and my opinion didn’t change… Moreover, for a long range project it is preferable to have the best workflow!

Since I used the Citrus Engine, I felt in love with physics engine and particularly Box2D. It is very useful & powerful for game development, but it has some hard constraints. With this project, I wanted to try an other physics engine. My choice was Chipmunk.

This post will not compare features, there are already a great post there, but how to move quickly from Box2D to Chipmunk. Thanks Scott Lembcke (Chipmunk’s author), for your clarifications.

Box2D : Box2D is an open source C++ engine for simulating rigid bodies in 2D. Box2D is developed by Erin Catto and has the zlib license. While the zlib license does not require acknowledgement, we encourage you to give credit to Box2D in your product. The manual.
Chipmunk : Chipmunk is a fast and lightweight 2D rigid body physics library written in C. The documentation.

Box2D uses meter/kilogram/second (MKS), Chipmunk uses pixel. There is no units for the mass, you defined the value you want, but stay logical between objects. The time is not clearly mentioned in Chipmunk, it doesn’t express in seconds but floats. Box2D uses real world units because it has a number of tuning threshold values, and the default values are set to be sane values for life-sized objects. Chipmunk’s algorithms mostly avoid the need for tuning values so that you can use whatever arbitrary units makes most sense to you (pixels, meters, inches, etc). Likewise for time and mass.

Box2D uses the term “world” whereas Chipmunk uses “space”. Both defined gravity & iteration step. Body’s gravity is difficult to manage in Box2D and Chipmunk if you want your objects to have a different one. You may set up a gravity(0, 0) to your world/space and manage the gravity into each object using a variable and updating its velocity.

Both have body’s center as registration point.

Box2D uses two objects to define a body : body (user data, position, velocity, forces, torques, impulse…) & bodyDef (body type definitions, and init values). Chipmunk uses only one object defining mass (which is automatically calculated in Box2D) and moment which represent inertia for the body.
Box2D has 3 body types : static, kinematic, dynamic ; Chipmunk kinematic bodies are named rogue.

Box2D fixture/fixtureDef defined shape, density, friction, restitution and filters. There is no fixture in Chipmunk. Restitution is the elasticity property on shapes. It doesn’t store density on a per shape basis though. You have to calculate that into the mass manually..

In Chipmunk, you can attach as many shapes to a single body as you need to in order to define a complex shape. Shapes contain the surface properties of an object such as how much friction or elasticity it has. It means than you can create a simple platform body and add all the shapes to it even if they are not close (a border bottom, a wall…).

With Box2D you can know dynamically which is the other body you collide, in Chipmunk you may use this method too. You may also defined a collision handler’s function between the typeA and the typeB with function references defining collision start/end & pre/post solve. In Box2D you managed collision thanks to the fixture, in Chipmunk you add the “listener” to the space.

CitrusEngine goes Stage3D with Starling

Hey folks, happy new year! My previous post go back from 1st december, I’ve been really busy : adding Starling in the CitrusEngine, learning iOS and working on my 2nd year school project. And obviously some great holidays between christmas & the new year.

Today I’m very pleased to share with you the Citrus Engine working on Starling! For those who don’t know it, it’s a platformer game engine using Box2D Alchemy and Signal libraries. However, it’s not only made for platformer games, you can use it for every 2D contents even if it isn’t a game thanks to its great Box2D management. So before this update, it has supported : Box2D physics, Signals event, a Sound Manager, a Console for quick debugging & tools, Input management, lots of defined objects like Hero, Baddy, Platform, Coin, Sensor, Moving Platform…, parallax, a Loader manager, level editors thanks to its own (the Level Architect made with Air), or using Flash Pro, or Gleed2D. 2 views : the flash display list and blitting, and a layer management!

Thanks to this update, the CitrusEngine now support the great stage3d framework Starling and I’ve also added 3 new objects Cannon, Teleporter & Treadmill, a Level Manager and an abstract class to store the game’s data. This two last things are optional you may use it or not. In this blog post I will explain how I’ve adapted the CE for Starling, and my updates with some examples. For a quick getting start with the engine please refer on its website or to the tutorials on this blog.

But let’s stop chatting, it’s time to test the demo :
Click here for the demo.

Continue reading CitrusEngine goes Stage3D with Starling

Box2D Sound Spectrum

This week is really challenging : my second year school project has started this week. It’s a team project with a graphic designer, a designer, a project manager and me as a developer. Our concept sounds very promising!

No matter, this short introduction explained that I’m really busy, so this experimentation is not perfect due to a lack of time…
Anyway, click here to see a sound spectrum made with Box2D and the Citrus Engine using BitmapData.

Continue reading Box2D Sound Spectrum

PhysicsEditor template for the Citrus Engine

Some months ago, I bought two softwares from code ‘n’ web : TexturePacker to create SpriteSheet and PhysicsEditor to create easily box2d object from png file.

Today, I’m happy to share my first extension / template for PhysicsEditor’s software : I’ve created a template to export physics object for the Citrus Engine.

This is a quick usage example
Click on the physical object and press tab. The console is now open. Then write : set Box2D visible false and you will see its picture. It matches really well to the physical object!

Continue reading PhysicsEditor template for the Citrus Engine

Create a ladder for the Citrus Engine

Hi, today a quick post about how to create a ladder for the Citrus Engine.
It is a preview version, Michael Kerr requested me for his flash game scripting class !

I’m working with Eric to add it into the original package !!

So here is the result : the ladder in action

Continue reading Create a ladder for the Citrus Engine

Teleporter, treadmill and cannon

After my game school project (Kinessia), I’m still doing some experiments with the Citrus Engine.

On its latest update, there was some new objects :
– a powerful particle system.
– new objects : missile, reward and reward box.

In this tutorial, I wil explain how to create new specific object which extends a Citrus Engine object.
At the end, we will have : a teleporter, a treadmill and a cannon that fires missile !
An ugly example.

Continue reading Teleporter, treadmill and cannon