A fast, easy to use, free, and community supported 2D game engine
indy2005
Member
Hi,
If you wanted to create a Box2D world where a car can drive almost infinitely either way (think Doodle Jump), how can you achieve this? I assume there must be limits to the size of a Box2D world...if not, would you have to pick up the body and move it to the start of the map instantly to give a continuous effect?
Regards
i
Moved to physics.
The size could be as big as you want. The limit is in how many bodies you are going to have.
robodude666
Member
Well, as of Box2D 2.1 (I believe) there is no longer a world boundary size. Prior to Box2D 2.1 when creating a b2World you had to include a b2AABB which included the bounds of the world. This requirement has been lifted. The bounds of the world are now infinite. If you need to imply a physical bound just do so programmatically. If the user jumps more than 1,000 miles in the air then stop them by applying an opposite force, etc.
Keep in mind, however that Box2D is designed to simulate small physics. Things are best simulated when small. If you create a static shape that's 1,000 miles high you may upset Box2D.
-robodude666
indy2005
Member
Thanks all,
So the question is...you want a phycis based car, to drive up the screen avoiding obstacles. You want to keep generating random stretches of track, with potentially no end....think Doodle jump, you just keep going up....hopw to handle that with Box2D physics controlling the car and collisions?
i.e. do you have to somehow "transport" the car back to the start occasionally and reproduce all forces to make it look seemless?
Regards
i
This may or may not work in your case, but I was working on something vaguely similar and what I ended up doing was to not move my hero forward at all, but just move everything else around it. A bit tricky to get everything synchronized properly, but once I got it figured out, everything worked fine. Something to consider anyways.
@indy2005
If you are programmatically creating your levels, as the player moves (lets say left to right), what you could do is destroy the physics bodies behind the player after a given distance. You could leave the ground but destroy the moving bodies that have no chance to react/contact with the player physics object. You could also destroy the ground objects that are away from the player (and re-create if needed). The key is to reduce the number of physics objects Box2D has to compute collisions and forces on.
indy2005
Member
Hi,
Thanks, I understand that concept I think, my issue is how do you let potentially the hero just continue moving right to left for ever. Do you not have to constrain the world somehow in it size and boundaries, or surround it by some static shape made of vertices (as per all B2D demos).
If you do have to constrain the workd - if a player reaches the end of the world - do you pick it up and somehow move it back somewhere in the world - but try to make it look seamless by recording and reapplying all forces? I am thinking a body must reach the end of its track/world at some point!
Regards
i
@indy2005 as @robodude666 mentioned above, in the new versions of Box2D, you do not need to define world boundaries. So you could keep expanding your world forever, but it eventually consume your CPU and memory.
Here is a quick test. Create a test project using the Cocos2D+Box2D template, comment out the ground body and put a CCLOG (or NSLog) display one of the physics block bodies X and Y coordinates (from Box2D). Notice how it keeps falling and falling and falling...
indy2005
Member
Hi,
Thanks. This is why I wanted to potentially recycle parts of the world, and drag the hero seamlessly back to an earlier part of the world after travelling 200m or so. The left and right boundaries could just be two static shapes I simply move into position left and right of the car and swap out as the car moves.
Not sure how to do it though (reposition the car seamlessly to an earlier position).
Regards
i
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