[RC] Box2D

Hi all,

It took me a while, I'm close to finishing the Box2D flash port.

There are a few problems caused by incompatibilities between the EXE and the Flash library of the Box2D libraries and I can't really fix these unless I invest a *LOT* of time - and even then I might not be able to. I've also dropped a few things because they are rather complex but not used very often, it seems.

Changes from the latest beta:

• More expressions.
• Contact filtering
• More stable object/body linkage
• All "create" (joint etc.) actions are now implemented.

Here's a list of what might not work:

• Ray-casting can go through walls in really rare, odd cases. This seems like a library issue.
• Edge chains work differently: Each edge is a shape in Flash. This causes some actions that modify edge chains to be unsupported.
• It seems like Box2D Flash handles sleeping differently. Bodies might fall asleep even if they shouldn't. You can manually disable sleeping for them or uncheck "Allow sleeping" in the properties.
• Body definition strings are not supported.
• Working with custom mass might cause unwanted behaviour! From what I know it should work, but it works a lot different in Flash, so it's a source for problems...
• Some expressions may not work properly at all. *SOME* - Most of them should work perfectly! It's just that I didn't have the time to test them all properly! RevoluteJointAngle seems to behave weirdly sometimes. I really have no idea why.

The testbed seems to work fine - except for the issues that I mentioned which are partially present there (the raycasting issue and Sticky Bodies 2 jiggles weirdly sometimes). So yeah, it seems like your chances of being successful when opening an old Box2D project and porting it to Flash are pretty high. :)

This is a Release Candidate - There's still room for bug reports. I just think this version is good enough from what I know - feel free to prove me wrong. Just note that I can't really provide 100% compatibility - the library differences make this way too difficult, sorry.

Grab it here:
http://clickteam.info/looki/Extensions/Flash/B2D.zip

Testbed:
http://clickteam.info/looki/Stuff/Testbed.html

Congratulations, you have been working hard on this!

Thanks! Update: 2 new fixes (bugs found by the great Outcast!). When linking an object, specifying "0 (no object)" for rotation now works (The body will rotate, but the Active won't). Also, the body type is now guaranteed to update every time you add/alter shapes (A body is static if all its shapes have a density of zero).

Thank you very much!

:D

Ooh! Can't wait to try this version! *Downloads*

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Originally Posted by Looki

Thanks! Update: 2 new fixes (bugs found by the great Outcast!). When linking an object, specifying "0 (no object)" for rotation now works (The body will rotate, but the Active won't). Also, the body type is now guaranteed to update every time you add/alter shapes (A body is static if all its shapes have a density of zero).

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Great :D I am humbled :)

wow! mind-blowing indeed :O thanks a lot for sharing this!

Do you have any tutorials or examples you could please put together on how to use at least a few of the features for Flash Apps? (Documentation, or walk throughs?)

Thanks =)

Based on the features I know are supported (based on Looki's list), I'm starting work on making a simple tutorial that focuses on flash Box2D, but also works for standard Box2D.

I've already finished Section 1: Differences and limitations in flash, so it's getting progress...

Looking forward to it!! =)

Wow, great happygreenfrog! I appreciate it, thanks :)

*Works on it some more*

Okay, sorry about the delay! The second section is done now, so I have a WIP version available, for those who can't wait. It has a example (which is very close to what you make in the second section), and the documentation (which also applies to the EXE version in the coding part of it). If you notice any errors in the tutorial (grammatical or coding), please let me know so I can fix it in the next version.

...I just ALT+F4'd the browser when I was done with my post. I'll try to write it again in short form:

Thanks for your documentation/examples! I appreciate the effort!

I'll explain some things:
The boundary properties actually have been removed from new Box2D library versions, in Flash they don't do anythign. Pos & Vel iterations pretty much what they do, how many iterations are used to process the body movement etc.
Timestep is a coefficient for how much time is processed each step. Should usually be set to 1/FPS, e.g. 0.02 for 50 FPS. Also, custom mass works in Flash now. There shouldn't be any weird results. I think.
Link destruction = If an object is deleted, so is its body and vice versa.

Anyway, thanks a lot for your help! :)

Okay, good to know. I'll revise my documentation based on that info. I'll put it in a new post here, not the old one, since I can't edit the post with the documentation.

Now I just need to know what "Unit scale" is...

I have a new revision made, but it doesn't have info on "Unit scale". The example remains unchanged, but is still included for those who don't have the previous version.

Thanks for your effort :D Lookin good.
Oh right. The unit scale is basically a coefficient between body (box2d) and object (mmf) coordinates. The default unit scale of 32 basically means that if you create an object at 64, 64, it will internally be created at 2, 2 (since 64/32 is 2). This kind of affects the way the physics are processed. All kinds of length units are divided by this unit length internally. Expressions like 'body X' would still return 64, since they internally multiply by 32 again. This is kinda useful if you want to use meter units, for example. With a unit scale of 32, a 32px object is exactly one meter tall. That means if you use 9.81 as Y gravity, you're accurately simulating earth gravity.

Okay! I guess it will need it's own sub-section in my documentation then, huh? It's kinda hard to make a short version of that in such a small space, so it just says "(Complicated, will be explained in a later section...)" I tried, and I couldn't even fit the last two sentences of your description of Unit Scale in it without it showing up on a new line. I can't have it so that it would be on a new line, because that would bump everything else down, so that's why I need to keep it short when editing existing parts of the documentation. Anyway, the updated version is attached.

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Originally Posted by happygreenfrog

Okay! I guess it will need it's own sub-section in my documentation then, huh? It's kinda hard to make a short version of that in such a small space, so it just says "(Complicated, will be explained in a later section...)" I tried, and I couldn't even fit the last two sentences of your description of Unit Scale in it without it showing up on a new line. I can't have it so that it would be on a new line, because that would bump everything else down, so that's why I need to keep it short when editing existing parts of the documentation. Anyway, the updated version is attached.

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This is really nice for beginner Box2D users. Will there be more advanced documentation in future?

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Originally Posted by Outcast

This is really nice for beginner Box2D users. Will there be more advanced documentation in future?

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It will get more advanced in the later sections, so yeah. It will get more advanced, and will turn a absolute beginner into a pro. Next section will probably talk about mouse joints. Once you have learned how to use those, you can then make a simple physics game where you just fling stuff around (simple, but at least it's got user interaction).

Does anybody think that mouse joints is a suitable subject for the next section of the tutorial?

I don't see why not. Are you having doubts?

Marv

No, I'm not having doubts, just checking with the people who are more experienced with making tutorials/documentation for MMF2 if it sounds good. I guess I'll start writing section three, then. Thanks for your feedback on the matter! *Begins writing*

Okay! The next section is complete! It's about mouse joints. (Thanks for the feedback Marv!)

Nice! Keep them coming :) Is it possible this will cover more advanced areas in the future? Like "soft bodies" and ropes?

It will cover ropes. I don't know what you mean by a "soft body", care to explain more? I already think I know what the next section will be about, and it's going to be more advanced.

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Originally Posted by happygreenfrog

It will cover ropes. I don't know what you mean by a "soft body", care to explain more? I already think I know what the next section will be about, and it's going to be more advanced.

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Sounds nice! :) With "soft bodies" I mean ways to simulate softness. It is used to do water type substances for example.

I don't know if Box2D has built-in support for that...

Quote:

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Originally Posted by happygreenfrog

I don't know if Box2D has built-in support for that...

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Its possible to create, I have seen some examples of it (not made in mmf though)
There are actually a lot of them out there. http://www.youtube.com/watch?v=VFkd_wqlx0A
I think I saw one that was made out of triangles, like a wheel.

But this is very advanced stuff I guess. Better to focus on the basics first maybe :P :D

It would be nice if you would cover joints in general in future! :)

Well, I'm not sure if I will cover anything that requires a very complicated work-around. Ropes are easy enough to make, but aren't going to be discussed in the next section. Instead, the next section will be a intro to polygons. However, I'm not going to be working on the documentation for a while, because I'm starting work on something else relating to 3D...

Thanks for your hard work Looki

I have a small problem, I'm unable to set the world-timestep to anything less than 1 (ingame). is there a workaround?


Trying to get my Delta in there, it works great outside of flash (ex timestep=0.02*delta).

It's been a while since I've update the documentation. I'll make a new thread for it once I have made a new revision. I think the next section will discuss something other than what I was originally planning on discussing.