Chipmunk Physics

Posted: **Thu Jan 01, 2009 9:17 pm**

Hi, Happy new year

I'm working on a game for Academic work and I use the very nice physics library Chipmunk. (dowloaded here: http://files.slembcke.net/chipmunk/rele ... Latest.tgz)

But after all my work and after checking all my project, a bug still here: the Segments (Static or active) don't generate collisions between them...

just see this screen capture:

http://fr.youtube.com/watch?v=YLpxWxfYhxM

don't make matter about the grey Circle, and the force which is apply to the segment, it's normal...

but see the 2 active segments and the top part of the balance (which is made with active Segments):
- the 1st fall and don't hit the top part of the balance (which is made with active Segments)...
- the 2nd turn and don't hit the 2 static Segments near its, but it hit the balls...
- then, the top part of the balance hit the balls, and the triangle (which is made with static polygon) but it don't hit the 1st segment...

in my code, the Chipmunk step are like that:

Code: Select all

if (m == INFINITY)
{
	_isStatic = true;
	obj = cpBodyNew(INFINITY, INFINITY);
}
else
{
	_isStatic = false;
	obj = cpBodyNew(m, 500);
}
obj->p = cpv(xpos, ypos);

....

if (_isStatic == false)
	cpSpaceAddBody(space, obj);
shape = cpSegmentShapeNew(obj, pos1, pos2, radius);
shape->e = e; shape->u = u;
cpShapeCacheBB(shape);
if (_isStatic == true)
{
	shape->collision_type = 3;
	cpSpaceAddStaticShape(space, shape);
}
else
{
	shape->collision_type = 1;
	shape->data = this;
	cpSpaceAddShape(space, shape);
}
cpResetShapeIdCounter();

finally, this 3 active segment shape which each one is linked with differents bodies, with the default group ( 0 ) and default layers ( (int) 65535 ), don't generate collisions with all others static or active segments

Can I find a solution or a fix here ? or maybe It can be my code ?

Posted: **Fri Jan 02, 2009 12:45 am**

Lack of segment to segment collisions is a known limitation. It simply has not been implimented yet.
see: http://www.slembcke.net/forums/viewtopi ... p=812#p812

The only workaround I can think of is to use a thin polygon instead of a line segment.

Regards,
AX

Posted: **Fri Jan 02, 2009 8:30 am**

oh, ok...

but how you made a thin polygon or a polygon line?

cpPolyShapeNew don't work with a numVerts at 1...

then, I tried this code for a polygon with 2 lines:

Code: Select all

		tab = (cpVect*)malloc(2 * sizeof(cpVect));
		tab[0].x = pos1.x;
		tab[0].y = pos1.y;
		tab[1].x = pos2.x;
		tab[1].y = pos2.y;
		if (_isStatic == false)
		{
			cpBodySetMoment(obj, cpMomentForPoly(obj->m, 2, tab, cpvzero));
			cpSpaceAddBody(space, obj);
		}
		shape = cpPolyShapeNew(obj, 2, tab, cpvzero);
		shape->e = e; shape->u = u;
		cpShapeCacheBB(shape);
		if (_isStatic == true)
		{
			shape->collision_type = 3;
			cpSpaceAddStaticShape(space, shape);
		}
		else
			{
				shape->collision_type = 1;
				shape->data = this;
				cpSpaceAddShape(space, shape);
			}
		cpResetShapeIdCounter();

But it don't work too

So how you can make that ?

Posted: **Sat Jan 03, 2009 10:48 pm**

I don't think a polygon shape would work with less than 3 vertices because the shape would have 0 area(nothing to collide with).

I was thinking of a thin rectangle when I said "thin polygon".

You could try replacing a line segment with: a rectangle with two parallel sides the length of the line, and the two remaining sides' length would be the "line segment" radius(must be greater than 0 in the case of a polygon though).

Chipmunk Physics

Bug... Segments don't make collisions between them

Bug... Segments don't make collisions between them

Re: Bug... Segments don't make collisions between them

Re: Bug... Segments don't make collisions between them

Re: Bug... Segments don't make collisions between them