[code] Verlet Rope « cocos2d for iPhone

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[code] Verlet Rope

(84 posts) (33 voices)

Started 2 years ago by patrickC
Latest reply from flightless

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RelicaGames
Member
@abitofcode, thanks for the help, I really should have thought to check to make sure dealloc was being called! I guess I just figured it was because I was getting the errors in the dealloc method when I tried to release some of those other objects. But anyway, it's working now, I wasn't actually calling release on the ropes, as I guess I thought they would be released when removed from my array!

But I still don't understand what's going on with, for example, this bit:
```
for(int i=0;i<numPoints;i++) {
	CGPoint tmpVector = ccpAdd(pointA, ccpMult(ccpNormalize(diffVector),multiplier*i*(1-antiSagHack)));
	VPoint *tmpPoint = [[VPoint alloc] init];
	[tmpPoint setPos:tmpVector.x y:tmpVector.y];
	[vPoints addObject:tmpPoint];
}
```
Why does tmpPoint not need releasing after calling alloc and init. Or is it because its a subclass of NSObject, and this is returning an autorelease object?

Thanks again for the help though!
Posted 1 year ago #
abitofcode
Administrator

Weird, adding an object to an array ups its retain count by 1, removing it reduces it by one. As the object above is not autoreleased it should be released after being added to the array so that its retain count becomes 1. The object would then be released when the array is released as it sends a release to each of the objects within it.

Does adding the release cause it to crash?

Posted 1 year ago #
RelicaGames
Member
Yes I thought that was how it should be, but yes adding a release after its been added to the array causes an error here:
```
-(void)dealloc {
	for(int i=0;i<numPoints;i++) {
		[[vPoints objectAtIndex:i] release];
		if(i!=numPoints-1)
			[[vSticks objectAtIndex:i] release];
	}
	[vPoints removeAllObjects];//Error on this line! - SIGABRT
	[vSticks removeAllObjects];
	[vPoints release];
	[vSticks release];
	[super dealloc];
}
```
Specifically, the error is:
malloc: *** error for object 0x615eb10: pointer being freed was not allocated.

But not having the release after its been added to the array works fine, and there are no longer any leaks according to instruments. So I find this very confusing!
Posted 1 year ago #

abitofcode
Administrator

-(void)dealloc {
	[vPoints release]; // this will send a release to all objects within the array
	[vSticks release]; // this will send a release to all objects within the array
	[super dealloc];
}

Posted 1 year ago #

RelicaGames
Member

Ahh yea that works, so really there's never any need to remove all objects before releasing! Thanks for the help! And thanks @patrickC for this rope class!

Posted 1 year ago #
cocos2der
Member

I don't really follow whats happening in the createRope, resetWithPoints, updateWithPoints and updateSprites of the Rope.mm class. could someone please help me.

Posted 1 year ago #
flightless
Member

hi,

we’re using a modified VRope 0.4 in our latest game (Bee Leader, http://www.flightless.co.nz/beeleader) so we’ve put the changes up on github at https://github.com/mb1/VRope.

Changes include initialising a rope using a b2RopeJoint (instead of two bodies, allows for more flexible anchor points), allowing for changing gravity, and a retina fix (tested on iPhone4s and iPad 3).

There’s still some testing, cleanup and other changes to be done, but it's working well. Thanks to @patrickC for the original code and tutorial.

cheers,

// greg
greg@flightless.co.nz

Posted 1 year ago #
mobilebros
Moderator

@flightless - The link to your game does not work, did you mean http://www.flightless.co.nz/projects/bee-leader/

Posted 1 year ago #
flightless
Member

@mobilebros yep, thanks. The forum code grabbed the closing bracket ) and applied it to the link :)

Posted 1 year ago #
tweedy2
Member

Hey guys, I just found the VRope and it's really awesome!! Did anyone fix the Dealloc Issue? I just cant get it working. In my Cocos2D 2.0 Scene I use the rope and it works fine but when I get to the GameOverScene and HelloWorldLayer dealloc is called I'm getting Bad Access all the time. I tried evrything you wrote here but it's permanently crashing... Do I have to do anything in my HelloWorld dealloc?? because anything in the VRope Dealloc seems to be wrong. I got the standard :
[ropeSprites release];
[vPoints release];
[Sticks release];

Any help SOOO appreciated!

Posted 10 months ago #
flightless
Member

It's not ported to cocos2d v2.x so it won't work directly, but compare what you've got in your init/dealloc with our update at https://github.com/mb1/VRope

Posted 10 months ago #
tweedy2
Member

Hey thx but I already tried it with your VRope. I get a SIGBART with "-[VRope init:body2:batchNode:]: unrecognized selector sent to instance 0xb074cd0" Do you have any Sample Project for Cocos2d 2.x? That would be so awesome!

Posted 10 months ago #
flightless
Member

No, sorry, we haven't ported anything to cocos2d v2.x so that will be the cause of the crash you just mentioned. Try comparing what you had working with our init/dealloc methods to see where your bad access might be. Also, you try using NSZombiesEnabled to see where it's being accessed (http://stackoverflow.com/questions/6991328/how-can-i-set-nszombiesenabled-in-xcode4).

Posted 10 months ago #
tetraweb
Member

On 1.1 I'm also getting the unrecognized selector error on
[code]
[VPoint setGravityX:0.0f Y:-0.98f];
[/code]

I must be missing something in setting it up to work with different gravity.

Greg

Posted 9 months ago #
flightless
Member

@tetraweb what version of VRope are you using? [VPoint setGravityX:0.0f Y:-0.98f] should work in the version of VRope 0.4 we put on github (https://github.com/mb1/VRope/blob/master/VRope/VPoint.h).

Posted 9 months ago #
Sandbird
Member

Hi,
Is there any way this can be used to 'skin' the pulley rope from the Box2D example ? Right now it has a debugdraw line only.
And if so, how ? Any ideas on what to change? (i guess besides the 2 points, given to the rope)

Posted 8 months ago #
flightless
Member

@Sandbird VRope makes a rope of constant length between two points, applies some gravity, etc. and simulates moving a range of internal points (each with sprites) between the control end-points. If you're ok with the rope not changing length (and perhaps drooping down with gravity when the pulley gets shorter) then you could just update the rope endpoints to your pulley locations. If you want to skin the pulley and have the rope adjust length to match then you'll have to use another technique or adjust VRope a bit to add/remove points and adjust the rope length as required.

Posted 8 months ago #
Sandbird
Member

@flightless, it would be so nice if pulley had VRope embedded in it T_T.
I guess i have to try and do it. Thanks for the info though. :)

Posted 8 months ago #
mijator
Member

While able to get VRope working (via Wenderlich tutorial) and impressed by it, it doesn't behave the way I was hoping because other bodies pass right through it, so while it looks like a rope it doesn't exactly behave like a real rope. I'm just wondering if anyone knows the best way to create things like: flexible bridge, ropes that collide with other bodies, ropes that character (bodies) can climb, strings (e.g. guitar string), etc., or is there a way to attach fixtures to VRope sticks?

Posted 4 months ago #
Ruenzuo.PE
Member

I have been using Verlet Rope class, It's fantastic! I'm working in a game with variable length ropes, wich I achieve by changing the max length of the joint by calling:

((b2RopeJoint *)_joint)->SetMaxLength(((b2RopeJoint *)_joint)->GetMaxLength() + 10/PTM_RATIO);

Everything works great with the joints, I checked with the debugger, but I cannot get the VRope class update the number of sprites it uses to represent the rope, for example, when I decrease the joint a lot, I get a little sag.

Could you help me? Let me know I you need more info, like project or screenshots.

Posted 4 months ago #
flightless
Member

@Ruenzuo.PE

from memory the original VRope code uses some hardcoded numbers to tweak things like sag. Check the source and test with some different magic numbers to see if it solves your problems with shorter ropes. If it works then you could update the VRope source to make it a variable and then set it based on the length/number of segments when creating your rope. I don't think it supports changing the number of segments/sprites during simulation but there might be some nice ways to tweak things to change the length/sag rather than destroying and recreating the rope.

I'd guess that changing the number of segments/sprites during a simulation would cause a noticable jump as the code would need to solve over a different number of points. You'd probably have to smooth/fix this if you changed the number of segments or simply destroyed and recreated the rope, depending on the usage in your game.

cheers,

// greg

Posted 4 months ago #
yetanothersignup
Member

I used a few days trying to figure out how the VRope, Box2d, cocos2d things work. I'm a newbie to all of them (but not to iOS dev, having 2-3 years of experience).
I guess some people asked how to cut the rope...
What I tried to do was release the box from the rope upon push of a button. It was kind of hard and I don't think I have an optimal solution yet. It seems that the VRope implementation always need two b2Bodies for the rope constraint itself, and then the graphical VRope too. What I ended up doing so far at the time of the button push is I destroy the original rope constraint, and in its place create a new one with body A being the same anchor body as in the first constraint. As for body B I created a new invisible body (that will not collide with any other bodies) and basically copy the values from the original body B (didn't find a clone method, so I recreated the body from the def, and copied the position. Might have to copy some more values like rotation, transformation (?) to make it really correct...). Also I modified VRope class to allow setting a new bodyB object. Didn't check for memory issues so far but it is working 85% ok. If the rope is in a tangled up position, it might get stuck (think Dilbert's necktie). Getting more used to cocos2d and Box2D, I hope I can fix that later. If someone else does not have a better idea?
My plan is to have a guy hang on to the rope, and allow the guy to jump off of it...

Posted 3 months ago #
Vavius
Member

You can make a "handle" body at the end of the rope (can be invisible) and attach it to the guy with weld joint. When jump off button is pressed you just destroy the joint.

Posted 3 months ago #
flightless
Member

No new changes, but moved our repo to http://github.com/gregharding/VRope (was http://github.com/mb1/VRope).

Posted 1 month ago #

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