cpPolyShape collision issues « cocos2d for iPhone

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cpPolyShape collision issues

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Started 2 years ago by DetectiveCakes
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DetectiveCakes
Member

Has anyone else had weirdness in dealing with collisions between cpPolyShapes and other shapes?

My situation is this: I have some static cpPolyShapes hooked up to a body with infinite mass. I have some cpCirclesShapes that are user controllable. If the user pushes one of the circle shapes against a poly, initially it behaves as expected and bounces away. But if the user keeps pushing it, eventually it sort of "squeezes" through the poly shape and pops out the other side.

A few notes:
-My cpPolyShapes are convex
-The vertices of my cpPolyShapes have been defined in a clockwise direction, in order
-I'm using cpBodySlew to push stuff around. Maybe a problem?
-I don't have this problem with cpCircleShapes hitting other cpCircleShapes or cpSegmentShapes
-Seems to happen most often at/near vertices of a cpPolyShape, and in places where two cpPolyShapes touch/overlap
-I'm not dealing with particularly high velocities or particularly small shapes

Any ideas? Anyone had similar issues, even if you didn't find a solution (just so I know I'm not losing my mind)?

Thanks

Posted 2 years ago #
pabloruiz55
Member

hi!
If i am not mistaken using cpBodySlew modifies the velocity of a body to have it move to the desired location. Maybe it is what is causing your problem... try testing with applyforce or applyimpulse.

From what you describe is the only thing i can think of.

Posted 2 years ago #
zombie
Member

Hi,

I would ask for this in the chipmunk forum. You will get an answer there pretty soon.

- Some ideas from me: Try not to use the slew function. I use a joint between a mouse body (controlled by the user touch) and the touched body. By this the joint will strech instead of forcing by the slew function the shape to the defined position.

- Try to increase the iterations or minimize the spaceStep interval.

I never tried the Slew funtion myself, but I am pretty happy with the way it works my way. (ps. I use the trunk of chipmunk, there are some joint features added that will improve the mouse grabbing stuff)

Hope this hekps somehow.

Zombie - We started our ZombieSmash Blog : http://zombiesmash.gamedrs.com

Posted 2 years ago #
DetectiveCakes
Member

Thanks guys! I was thinking it might be something to do with cpBodySlew, and I really need to move to something more robust than that anyways for other reasons. So, first test will be to ditch that. I like your joint idea quite a bit.

That or ditch chipmunk and move to box2d, which has been tempting me for a while.

For now, it's time for TV and beer. Ahhhh, short term solutions...

By the way, I cross-posted to the chipmunk forums, will update here if they have anything interesting to say for future reference.

Posted 2 years ago #
zombie
Member

Remember to take a look at the chipmunk trunk. The demo in there shows how to implement mouse dragging.

Zombie - We started our ZombieSmash Blog : http://zombiesmash.gamedrs.com

Posted 2 years ago #
vutronic
Member

"If the user pushes one of the circle shapes against a poly, initially it behaves as expected and bounces away. But if the user keeps pushing it, eventually it sort of "squeezes" through the poly shape and pops out the other side."

I'm experience a similar issue with the poly shape too. Please let me know if you've found a fix. I have a moving platform done with poly shape. In the game, a vehicle can jump on it. It looks like the collision detection is not very accurate between circles( wheels of the vehicle) and poly shapes.

Posted 2 years ago #
DetectiveCakes
Member

The chipmunk author seems to think it's a bug with chipmunk.

Here is a link to the thread over there, with a few more details (not many):
http://www.slembcke.net/forums/viewtopic.php?f=1&t=647

Posted 2 years ago #
DetectiveCakes
Member

Came up with kind of a silly work-around that seems to work acceptably. Basically, any time I create a poly shape, I create a circle shape near each vertex that sticks out about a pixel outside of the poly.

It's not ideal... there's a little more overhead, but circles are well enough optimized in chipmunk that I'm not noticing any measurable performance hit. Once in a great while I still slip through though, which is annoying...

Posted 2 years ago #

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