Be my fan on FacebookBox2D: tutorial for the absolute beginners
- January 27, 2009 by Emanuele Feronato
- Filed under Actionscript 3, Box2D, Flash | 49 Comments
This is a tutorial about Box2D dedicated to the absolute beginners.
I received a lot of request asking for this, so here we go.
What is Box2D
Box2D is a feature rich 2d rigid body physics engine, written in C++ by Erin Catto.
There is a Flash version called Box2DFlashAS3, but among Flash developers it’s called Box2D as well, that you can download from this link.
Being a Flash porting, we will use AS3 to make our project, instead of C++ as required by the original library.
Once you downloaded and unpacked the zip file in a folder, this is what you will get:
You are now ready to begin
Your first Box2D experiment
Start Flash and create a new AS3 Flash file and call it (example) demo.fla. Save it in the same folder you used to unzip Box2D package. Also in your properties panel assign the Class name to (example) demo, this way:
Now create a new actionscript file, call id demo.as and save it in the same folder.
Your folder now should look this way:
it’s time to edit demo.as
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 | package { import flash.display.Sprite; import flash.events.Event; import flash.utils.Timer; import flash.events.TimerEvent; import Box2D.Dynamics.*; import Box2D.Collision.*; import Box2D.Collision.Shapes.*; import Box2D.Common.Math.*; public class demo extends Sprite { public var the_world:b2World; var time_count:Timer=new Timer(1000); public function demo() { var environment:b2AABB = new b2AABB(); environment.lowerBound.Set(-100.0, -100.0); environment.upperBound.Set(100.0, 100.0); var gravity:b2Vec2=new b2Vec2(0.0,10.0); the_world=new b2World(environment,gravity,true); var debug_draw:b2DebugDraw = new b2DebugDraw(); var debug_sprite:Sprite = new Sprite(); addChild(debug_sprite); debug_draw.m_sprite=debug_sprite; debug_draw.m_drawScale=30; debug_draw.m_fillAlpha=0.5; debug_draw.m_lineThickness=1; debug_draw.m_drawFlags=b2DebugDraw.e_shapeBit; the_world.SetDebugDraw(debug_draw); var final_body:b2Body; var the_body:b2BodyDef; var the_box:b2PolygonDef; the_body = new b2BodyDef(); the_body.position.Set(8.5, 13); the_box = new b2PolygonDef(); the_box.SetAsBox(8.5, 0.5); the_box.friction=0.3; the_box.density=0; final_body=the_world.CreateBody(the_body); final_body.CreateShape(the_box); final_body.SetMassFromShapes(); addEventListener(Event.ENTER_FRAME, on_enter_frame); time_count.addEventListener(TimerEvent.TIMER, on_time); time_count.start(); } public function on_time(e:Event) { var final_body:b2Body; var the_body:b2BodyDef; var the_box:b2PolygonDef; the_body = new b2BodyDef(); the_body.position.Set(Math.random()*10+2, 0); the_box = new b2PolygonDef(); the_box.SetAsBox(Math.random()+0.1,Math.random()+0.1); the_box.friction=0.3; the_box.density=1; final_body=the_world.CreateBody(the_body); final_body.CreateShape(the_box); final_body.SetMassFromShapes(); } public function on_enter_frame(e:Event) { the_world.Step(1/30, 10); } } } |
Lines 2-5: some commons Flash libraries used to make the demo
Lines 6-9: Box2D libraries… it’s not that important at the moment to know everything about them… they’re just some libraries
Line 11: Declaring the_world variable, b2World type. b2World is the the main object to deal with the Box2d engine. It stores all the joints and bodies, handles listeners and is responsible for stepping through the simulation.
Line 14: Declaring the_environment, b2AABB type. The physics environment generated by Box2D is not infinite, and b2AABB is the container of such environment. Think about it as a bounding box. Inside this bounding box, the world is ruled by Box2D physics.
Lines 15-16 : Defining the upper and lower corners of the environment bounding box, in meters. 1 meter = 30 pixels. So our box has sides made by 6000 pixels. They’re pretty too much for a single-screen project, but if you are using scrolling, it could be useful to set up a big environment. For more information about pixels and meters refer to Understanding pixels and meters with Box2D and how to select an object with mouse – part 2.
Line 17: Declaring gravity variable, b2Vec2 type. b2Vec2 is a vector with x and y components.
Line 18: Starting up the world: the constructor has three parameters: environment, the worldAABB bounding box, gravity the world gravity vector, and a boolean set to true to improve performance by not simulating inactive bodies.
And now you created the world. Next time I’ll explain the rest of the script
Anyway, this is the result
And this is the source code to download.
I hope this will help you start playing with Box2D.
(53 votes, average: 4.51 out of 5)
Loading ...They can be easily customized to meet the unique requirements of your project.
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YES!
finally a box 2d tutorial i can understand!
this actually might make me migrate to AS3…
Awesome!!
Thanks a lot!
You are really the rockstar of programming
make it PROgramming
thanx emanuele for making a tut for Box 2D that is for begginers
i haven’t started AS3 yet, but i think this will help…
do u have a beggining AS3 tutorial
Very basic for my taste. But you can’t satisfy everyone :)
Glad you got a good response from your other users.
Keep up the more advanced tutorials too.
[...] Box2D: tutorial for the absolute beginners [...]
XD
Excellent!
I shall be closely following both the basic Box2D tutorials tonight and start playing around with them!
[...] Box2D: tutorial for the absolute beginners [...]
It looks great, but when i’m trying to open “demo.fla” file in Adobe Flash CS3, I got the message “Unexpected file format”. Do you know why?
[...] you followed Box2D: tutorial for the absolute beginners, then you know you can put some object to “sleep” to improve performance by not [...]
[...] a mix of your tutorials about “Box2D for absolute begginers” and “Totem Destroyer Prototype“. I also added some other features, such as the [...]
Hi,
I wanted to know if there was an easy way to add a texture to those ‘boxes’..
Thx
Fabien
uuuh, yeeeah, that’s so PROOO Mr. PROgrammer
Thanks a lot!!!!
Can you put it in a Flash CS3 format?
Or do I NEED Flash CS4?
If I do, that would suck! :(
[...] Boy Wonder!!) Emanuele Feronato (an Italian PROgrammer) has written an extremely useful tutorial: box2d tutorial for the absolute beginners/. This one is a very good starting [...]
Nice guide, might play around with it sometimes.
Also, hi Fighterlegend!
to Fighterlegend:
no you do not NEED CS4 for this,
this can also be done in CS3 with ease.
PS: awesome tutoial 5/5
Why don’t you reply to peoples questions?
Nice tutorial. I’m still learning as3 and this will be very useful. Thanks!
[...] want to give yet another shout out to Emanuele Feronato. If you are looking at this code, and are completely lost, he has EXCELLENT tutorials to get you [...]
This one help me start off on the right foot. And all your other tutorials are awesome! I was able to expand on this to turn the boxes into dynamic falling text.
(^_^)// Cheers.
Thank you very much.^_^
Thanks for these, really finding them useful.
One thing though, you mentioned that 1 meter = 30 pixels… is that a default or do you have to set that ratio somewhere in the code?
Thanks again.
Thank you for the lovely tutorial, its beyond amazingly useful. As a low to mid-level Flash progrommer / animator, getting a handle on the Box2D stuff through just the examples is actually quite difficult (and not helped by the slightly more ambiguous naming conventions it uses)
But seriously, amazing stuff. Thanks :)
I don’t seem to have flash, to create a new AS3, I need help. Can you give me a link?
Can u pls explain the rest of the script
Errm.PART 2!!!!!!!!!!!!!!!!!!!!!?????????????????
HAHA! I found it XD
http://www.emanueleferonato.com/2009/01/29/box2d-tutorial-for-the-absolute-beginners-step-2/
:D
i followed the directions exactly as listed, however when i try to run the program, it gives me a bunch of errors starting with:
1046: Type was not found or was not a compile-time constant: b2World.
1046: Type was not found or was not a compile-time constant: b2AABB.
1046: Type was not found or was not a compile-time constant: b2Vec2.
anyone have any ideas?
@clayton
your classpaths arent correct configured..
these errors happen when flash or your code editor cannot find the class you are trying to use..
So check your linkage to the classes and try again :)
it also helps to get a basic understanding of AS3.0 and OO before you start a tutorial like this one.
;)
ok. I tried this and it was an epic fail.
The idiots who made Box2d decided to randomly change the whole thing! The box2d looks nothing like the screenshots you had. Could you plz make a new tutorial?! thanks.
I got the same error with #26.
Help pls ><
[...] About a year ago I published a Box2D tutorial for the absolute beginners. [...]
Hi, guys.
You need to have the following in order to successfully run Demo.fla.
1. Adobe Flash CS4
2. Box2DFlashAS3_2.0.2
Download Box2DFlashAS3_2.0.2 in here.
http://sourceforge.net/projects/box2dflash/files/
If you have any questions, ask. :-)
Thank you for the great tutorial, Emanuel! You rock!
Sam
hello,
i liked very much the scene i see in the last animation screen.
now i want to ask whether it is possible to write an application without using flash development environment? i am a newbee in software developing but i like flash applications too. but i am a student and no have money for flash development environment.
is there a compiler for action script desperate from flash development environment?
i googled a bit but find nothing.
thanks for tutorial and any possible advises.
I tryed this code with Adobe Flash IDE CS4 : It’s okay.
When I try with an AS3 project with Flash Develop, debugDraw doesn’t display any objects.
I use : FlashDevelop 3.0.6/Box2D 2.0.2/Flex 3.4
Learning AS3 and your tutorial is an awesome way to experiment. Really one of the best sites I’ve found about Flash, Actionscript, and games. Thanks for sharing your knowledge.
hii those whor getting error just like #26 and #29 check out this link http://orenyomtov.com/topic/flash
i had the same error i got it sorted nw.
Great tutorial. I’m very excited in box2d. Hope you can give more..
[...] Einsteiger Tutorial von Emanuele Feronato: http://www.emanueleferonato.com/2009/01/27/box2d-tutorial-for-the-absolute-beginners/ [...]
Hey Emanuele, Nice tutorial though the box 2d files i downloaded had nearly 60 to 70 syntax errors like the one below all was same error
1084: Syntax error: expecting identifier before lessthan.
public var m_vertices:Vector.;
the use of this bracket caused a lot of problems
Doesnt work i dont know why
do i have to put it in a special rute in flash installation directory?
hi,
A very simple and nice tutorial and followed all the instruction as said in tutorial but i got 10 compile time errors :- 1084: Syntax error: expecting identifier before lessthan. all the errors were same. I am using FLASH CS3. I created demo myself since i am not having CS4. Thanks for such a b’ful tutorial.
Great tutorial, with the latest version there were a lot of errors, but after downloading the previous version Box2DFlashAS3_2.0.2 all worked great without any errors.
Thanks for this tutorial!
Thanks! Great easy-to-learn tutorial!
hi Emanuele,
10x for this tutorial
I think you should consider update it. I saw that in the latest B2Box – there is now more public b2DebugDraw.m_sprit instead we have b2DebugDraw.SetSprite()
If either of you (readers of this tutorial) encountered this problem – I hope I helped.
The way I solved this, is by going to decleration of class b2DebugDraw, and looking for m_sprite.
Best Regards, Shefy