We were asked to help fixing the A8 version of the A7 Ragdoll demo by Helghast. As this is a good example of the problems you can encounter when converting an A7 ODE project to A8 PhysX, I'm posting here our experiences as case study.

1. Continous collision detection

For speed reasons, PhysX does not use CCD by default. This causes very small objects, such as the tiny bones of the demo, to fall through the floor. So you need to activate CCD when tiny things move fast and collide with something.

Code:
// A7 physics initialization
	fps_max = 60;
	fps_min = 30;
	
	ph_iterations = 20; // set itterating physics to smooth out.
	ph_setgravity(vector(0, 0, -668)); // set gravity
	ph_setcorrections(9000, 0); // set physics corrections
	ph_setcollisions(1000, 20);

Code:
// A8 physics initialization for CCD
	physX_open();
	pX_setgravity(vector(0, 0, -9.81)); // set gravity
	pX_setccd(1);


2. Initialize physics objects

Begin with the default settings. They will suffice in most cases. Adjust them later if necessary. The mass is calculated automatically in A8.

Code:
// A7 physics object initialization
	set(entityMe, PASSABLE);
	phent_settype(entityMe, PH_RIGID, PH_BOX);
	phent_setmass(entityMe, mass, PH_BOX);
	phent_setfriction(entityMe, 15);
	phent_setdamping(entityMe, 35, 35);
	phent_setelasticity(entityMe, 35, 30); // bounciness
	reset(entityMe, PASSABLE);

Code:
// A8 physics object initialization with CCD
	pXent_settype(entityMe, PH_RIGID, PH_BOX);
	pXent_setccdskeleton(entityMe, nullvector, 1);


3. Initialize joints

In A8, joints are addressed through the entity pointer, not through a hinge handle, and have more parameters (for instance restitution, and break limits). When you don't need a break limit, pass NULL for the vector parameter. Passing nullvector would set the break limits to 0. And don't join an object with itself! This will cause a crash, just as in real life.

Code:
// A7 hinge initialization
	var tempHinge;
	// make constraint
	tempHinge = phcon_add(PH_HINGE, constr_1, constr_2); // attach to bodypart
	phcon_setparams1(tempHinge, constr_1.x, RD_Hinge1, nullvector); // set hinge limits
	phcon_setparams2(tempHinge, RD_Hinge2, nullvector, nullvector);


Code:
// A8 hinge initialization
	// make constraint
	pXcon_add(PH_HINGE, constr_1, constr_2, 0); // attach to bodypart
	pXcon_setparams1(constr_1, constr_1.x, RD_Hinge1, NULL); // set hinge limits
	pXcon_setparams2(constr_1, RD_Hinge2, NULL, NULL); // same


4. Reading object positions

Don't disable or enable objects for reading their positions in A8. First, it is not necessary. Second, you can't displace objects that are attached to joints, so disabling an object requires removing its joints first. You don't want to do that for a ragdoll.

Code:
// A7
	pXent_enable(limb, 0);
	vec_for_bone(limb.x, actor, boneBlend); // place at right position
	ang_for_bone(limb.pan, actor, boneBlend); // rotate by right angle
	pXent_enable(limb, 1);


Code:
// A8
	vec_for_bone(limb.x, actor, boneBlend); // place at right position
	ang_for_bone(limb.pan, actor, boneBlend); // rotate by right angle