Chipmunk Physics

Trying to make a ragdoll. Knees should not bend forward, right?

Of course, it is achievable with collision shapes... but that sucks.
Help! Urgently need better ideas!

It seems that I'm not the first one who asked this question. Oops.
http://www.slembcke.net/forums/viewtopic.php?f=1&t=44

But i have another question:

I want the ragdoll to hold its pose. This was my plan: Red dot is the pivot, blue thing - cpDampedSpring with rest length a bit longer than the distance between anchors.

Plan did work, but not too well... lot's of glitches.
Any suggestions for plan B?

What was the issue? That should work alright.

Doing more testing right now. Maybe I was wrong about cpDampedSpring causing glitches. I'll share my results here.

As for angle limitations, I used additional shapes instead of slide joints... works very nice... why the hell did I think that additional shapes sucked (see my first message)…

Haven't played around with spring yet. Looks like I won't be needing it anyway.

Let's discuss general ragdoll making issues here. Topic of the message has been accordingly changed.

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I'm working on a ragdoll-based game for iPhone, that's why ragdoll has to be as cpu-effective as possible.
My current ragdoll:
Red thingies limit the angles.

I really like how my ragdoll works, but keep wandering if additional shapes are more or less cpu-effective than using slide joints.

I'd be really grateful for all cpu-time-saving ideas.

Slide joints should be way cheaper than using more shapes. It's a simpler constraint, and doesn't require all of the hullabaloo that goes into collision detection.

And they are easier to use, as I have just discovered.

Should have used them from the beginning instead of wasting time with shapes.

New problem.

I need a way to address different body parts of N different ragdolls.
Like this:
player1.head->f.x=1000;
or
player2.shinR->t=-20000;

My plan was to create a RagDoll structure with cpBodies embedded in it.

typedef struct RagDoll
{
float BodyLength;
float BodyFat;
.... blah blah blah...
float Flexibility;

cpBody *head, *shinR, *thighR... etc etc;

}RagDoll;

Next step was writing a ragdoll-adding function.

void adddoll(RagDoll doll) //there is no space parameter yet, because currently I’m only using one space.
{

float BodyLength=doll.BodyLength;
float BodyFat=doll.BodyFat;

.... blah blah blah...

doll.head = cpBodyNew(0.2, cpMomentForCircle(0.2, 0, abs(SKX)*HeadSize, cpvzero));
doll.head->p = cpv(initX+SKX*(HeadSize/5), initY+SKY*(BodyLength/2+HeadSize));
cpSpaceAddBody(space,doll.head);

}

Ragdoll appears, but I can't address it's head. If I do, error appears "Unhandled exception at 0x004049cc in Chipmunk4MSVC2k3.exe: 0xC0000005: Access violation writing location 0x00000024."

Ok. Plan B.

cpBody *head; //additioanal cpBody
void adddoll(RagDoll doll)
{
.... blah blah blah...

head = cpBodyNew(0.2, cpMomentForCircle(0.2, 0, abs(SKX)*HeadSize, cpvzero));
head->p = cpv(initX+SKX*(HeadSize/5), initY+SKY*(BodyLength/2+HeadSize));
cpSpaceAddBody(space, head);
doll.head=head;
}

Same thing.

Plan C.

void adddoll(RagDoll doll)
{
.... blah blah blah...
cpBody *head; //additioanal cpBody, declared outside the function and structure

head = cpBodyNew(0.2, cpMomentForCircle(0.2, 0, abs(SKX)*HeadSize, cpvzero));
head->p = cpv(initX+SKX*(HeadSize/5), initY+SKY*(BodyLength/2+HeadSize));
cpSpaceAddBody(space, head);
}
player1.head=head;


It works! And it works with any number of players! But that's not very convinient.

adddoll(player1);
player1.head=head;
player1.shinR=shinR;
......................

adddoll(player2);
player2.head=head;
player2.shinR=shinR;
.....................

adddoll(player3);
player3.head=head;
player3.shinR=shinR;

etc etc etc

That sucks.


Why, why

adddoll(player1);
.................
doll.head=head; INSIDE the function

is not equivalent to

adddoll(player1);
.................
player1.head=head; OUTSIDE the function



I know it's not a chipmunk question. But I just don't get it (and can't find the answer in the net). Maybe someone here will help me.

Or maybe you can suggest a different method of addressing different parts of a ragdoll (presuming there are N automatically generated ragdolls)?

p.s.: Sorry for my not-so-good English.

You have to make sure to allocate memory for any structure and pass in a pointer to it.
It's been awhile since I've done pure C structs (C++ and Obj-C now) so this may not be exactly right.

You could try:
void adddoll(struct RagDoll doll)

{


}
or alternately:
struct RagDoll doll, *dollPtr;
dollPtr = &doll;
dollPtr->head = 10;
void adddoll(dollPtr *doll)
{
doll->head = 10;
}

take a look at teh engine code to see how it's handled and check a C reference on passing a structure to functions.