cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   chrisco
   Member

   In my game, I have a constant stream of missiles - my goal is to have the missiles fly along a path that's randomly chosen from a collection of possible paths. What I'm not sure about is how to handle this with Box2d-based collision and physics.

   My current plan is to move my AtlasSprite using a BezierBy action, and to update the position of a b2Sensor with each tick in my physics system to match the sprite. I think this will work, but I'm not sure how expensive it is or what kind of control I'll have over collision reactions.

   My preferred plan would be to apply forces to the missiles to approximate the path, and to have full benefit of the physics system.
   My knowledge of Box2d (and physics engines in general) is pretty limited, though - would something like this be possible? My best guess would be to constantly look at the path ahead of the missile and apply impulse and torque to maintain the path and rotation. Seems like it would be pretty tricky to keep a smooth, natural motion at a consistent velocity.

   Anyone else have any ideas on this? The paths will be fairly complex (more so as the difficulty increases in the game), so a simple direction and constant force won't really do the trick.

   Thanks for reading, and for any suggestions/guidance,
   Chris

   Posted 2 years ago #
2. 

   yarri
   Member

   Hi, I don't mean to be sarcastic but... you could just "fire" the projectile by applying a force with a vector and let the engine work. Look at the box2d code for the "LaunchBomb" code in the test framework, this might be all you need.

   --yarri

   Posted 2 years ago #
3. 

   chrisco
   Member

   Thanks Yarri - I did think about that, but I want to have a certain level of control over the paths that the missile takes. As the difficulty in the game increases, the missiles will zig-zag and loop around the screen (to be avoided by the player). I don't want this to be completely random, which is why I'd prefer to use preset paths.

   Thanks again for taking the time to look over my questions.

   Posted 2 years ago #
4. 

   pabloruiz55
   Member

   I am thinking you could do something like this:

   -When launching missile store the launch and destination position.
   -Make the missile move towards the destination position applying impulses.
   -This will make the missile go in a straight line towards the destination. (suppose it is moving horizontally from left to right)
   -Now you could apply an upwards/downwards impulse to it in somepoint while it is moving towards the destination.
   - To make it zigzag you would apply an upward impulse at 1/3 of its path and a downward impulse at 2/3 of its path.

   Decalimer:Not sure about this ;)

   Posted 2 years ago #
5. 

   chrisco
   Member

   I think I might give that a shot, though I'll still lose some control. My biggest concern with random paths is the possibility of the path being unfair to the gamer in the earlier stages. I'm sure that I can find some way to balance it though. Thanks for the help :)

   Posted 2 years ago #
6. 

   Nalin
   Member

   I think it may be difficult to achieve exactly what you want, but one possibility is to set up box2d sensors along the potential path and when an object lies within it you could try applying forces/impulses.

   If you want to use preset paths then you can use body->SetXForm() to simply set the angle and position directly - and use it just for collision detection, though it does kind of defeat the purpose of box 2d.

   HTH

   Nalin

   Posted 2 years ago #

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