Collision problem of two bodies « cocos2d for iPhone

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Collision problem of two bodies

(5 posts) (3 voices)

Started 1 year ago by cocosboy
Latest reply from max9xs

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cocosboy
Member
I have two cpBodies, a hero and hurdle in my game play. when ever they collide I call a function and these two bodies are received in it. I need to stop both of these bodies.

I am using this code to stop them
```
static int Collisionfunction(cpArbiter *arb, cpSpace *space,  void *unused)
{
     cpShape *a, *b;
     cpArbiterGetShapes(arb, &a, &b);
     a->body->v = cpvzero;
     b->body->v = cpvzero;
     return  1;
}
```
Problem is that when they collide first time they are stopped. when I navigate player to go the opposite side from hurdle and again this collision function is called and player is unable to move again.

any idea to move player second time after first collision with hurdle.

I know it can be done using a BOOL flag to check its first time or second time. But I wish to do this with out using flag.

any idea?

thanks in advance
Posted 1 year ago #
itlgames
Moderator

Usually to avoid this problem you do collision detection based on future coordinate positions, so e.g. before you move your character, you calculate his next x,y position, and do the collision detection, if it's free to move, you move it, if not, you don't. I find this way much much better on all kind of games I have ever developed.

Posted 1 year ago #
cocosboy
Member

thanks for reply

as we know collision detection is being done by chipmunk automatically.

first thing is that how can I get future coordinates (if I am not wrong, its front point of my player direction?) of my player?

secondly once I have got the front point. How I will detect collision from that future point.

Posted 1 year ago #
itlgames
Moderator

I'm not sure about chipmunk, but I reckon if you used it, there must be something wrong on the way you used it, cos I am sure chipmunk does collision detection correctly, but I can't help there cos I am not familiar with chipmunk.

Anyway there must be few ways to do collision detection, what I do is, in 2d, assume each sprite is inside a rectangle or circle (depends of shape), so you know x,y coordinates and size of rectangle or radius of circle, you also know coordinates and shape of your enemies, so is just simple maths to detect a collision between two rectangles or two circles.
To check future position, you just calculate what is going to be the next position of your character, so you have x+dx,y+dx, where dx,dy should be the amount you should move on next frame.

Posted 1 year ago #

max9xs
Member

@cocosboy... in the first time when the collision performs change the collision type of it.. like

static int Collisionfunction(cpArbiter *arb, cpSpace *space,  void *unused)
{
     cpShape *a, *b;
     cpArbiterGetShapes(arb, &a, &b);
     a->body->v = cpvzero; // hero
     b->body->v = cpvzero; // hurdle

    b->collision_type=4;
     return  1;
}

Now check for the hero and hurdle with collision_type =4 and return 0; implementation..

Collision problem of two bodies

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