Best way to simulate ships « cocos2d for iPhone

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Best way to simulate ships

(6 posts) (4 voices)

Started 2 years ago by Sexxypants
Latest reply from georgeburns

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Sexxypants
Member

Hey guys,

This is my first topic post (woot), hopefully somebody can help. Admittedly, I've posted this in the chipmunk forum as well, but it seems to be less active than cocos2d forums.

Getting down to it, I'm looking to simulate some boats moving around the screen. I used the bit of hackery in this post: http://www.slembcke.net/forums/viewtopic.php?f=1&t=873&p=4043&hilit=path#p4043 in order to get my boats moving along a "path." That's all fine and dandy if I tweak some of the parameters, but when they collide, they usually end up getting stuck to each other. And no matter what I do, I can't move them apart (the ships can't rotate with enough force to move the other ship away, so both of them can't move away).

What I really want is for the ships to collide initially, but sort of repel each other mildly so they're never stuck together. It's not necessarily realistic, but I just don't want my ships in a place where they can't move apart. I've set up some sensors on the ships, so I know when another ship enters my sensors, I'm just a little lousy on the physics part of it. It's almost like two magnets repelling each other, and I wasn't able to decipher how to get that done from the chipmunk electric/magnetic demo.

Anybody have any good idea on how to simulate this? I'd even settle for some ideas on how to move the ships around in a more accurate manner. I guess I'm saying I'm a bit short on ideas, and any would be appreciated.

Thanks,
-Paul

Posted 2 years ago #
Tone
Member
You should be able to setup a Collision handler that you can then tell the two shapes/sprites to do something different to get unstuck.

I am moving my objects around the screen and using chipmunk for different effects. When they bump into each other rather than have them keep going I set up a handler to detect the collision and then tell each Object to go the opposite direction.
```
cpSpaceSetDefaultCollisionHandler(space, &begin,nil,nil,nil, nil);

static int
begin(cpArbiter *arb, cpSpace *space, void *unused) {
	cpShape *a, *b;
	cpArbiterGetShapes(arb, &a, &b);
	if(a->data) {
		[((Star*)a->data) goOppDir];
	}
	if(b->data) {
		[((Star*)b->data) goOppDir];
	}
	return 1;
}
```
I hope that helps.
Posted 2 years ago #
Sexxypants
Member

Right, right, I'm doing a similar thing by calling a similar function when one ship collides with another ship's sensor.

I guess my question was more about a certain type of reaction. I don't want it to be cut and dry, collision = turn around. I would prefer that when you're a certain distance from another ship, you sort of drift apart slightly (like when you're within the sensor range). Like a magnet, you just get pushed a certain distance away before remaining at rest there.

Do I just take the points of contact and apply a force in the direction of the normal of that contact point?

Posted 2 years ago #
patrickC
Member

I would calculate the vector between the two ships rather than using the contact normal.
Then decide how much force to apply based on the distance between the two.
Apply an equal amount of force on each ship with opposing vectors and that should do it smoothly.
good luck

Posted 2 years ago #
georgeburns
Member
you could mod the gravity, so that when a ship is closer to the another it gets repelled. Take another look at the gravity magnetic demo. It took a while to wrap my head around... but I was able to make a test with two planets with their own gravitational fields... and about 100 objects floating around them.

the gravity update function on your boats would work something like this...
```
g = cpvmult(cpvsub(p,planet1),-30000.0f/(cpvdistsq(p, planet1)) );
g = cpvadd(g,cpvmult(cpvsub(p,planet2),-30000.0f/(cpvdistsq(p, planet2))));
```
except not planets... you would use ships, and a positive value instead of a negative one to make them avoid each other. The closer they get the more powerfully they would be repelled.
Posted 2 years ago #
georgeburns
Member

oh.. and you can just repeat that second line for each additional ship to avoid.
if there were a ton of ships or a variable amount, you could just loop it.

Posted 2 years ago #

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