make springs use fps- and physics-engine independent movedir values:

_x = spring constant (also applies to internal constraints), set to -1 for "ultra-hard" joint
_y = maximum spring force to apply (0 = no spring)
_z = dampening (only works if _y is not 0)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@9378 d7cf8633-e32d-0410-b094-e92efae38249

diff --git a/world.c b/world.c
index 6c93517c07531ee9918bd70ceeaaa5dc046009f2..6aa27808130df41dd4ce8b2fc33460c8130a99d8 100644 (file)
--- a/world.c
+++ b/world.c
@@ -1742,6 +1742,20 @@ static void World_Physics_Frame_JointFromEntity(world_t *world, prvm_edict_t *ed
                enemy = 0;
        if(aiment <= 0 || aiment >= prog->num_edicts || prog->edicts[aiment].priv.required->free || prog->edicts[aiment].priv.server->ode_body == 0)
                aiment = 0;
+       // see http://www.ode.org/old_list_archives/2006-January/017614.html
+       if(movedir[0] > 0)
+       // we want to set ERP? make it fps independent and work like a spring constant
+       // note: if movedir[2] is 0, it becomes ERP = 1, CFM = 1.0 / (H * K)
+       {
+               float K = movedir[0];
+               float D = movedir[2];
+               float H = (!strcmp(prog->name, "server") ? sv.frametime : cl.mtime[0] - cl.mtime[1]) / world->physics.ode_iterations;
+               float R = 2.0 * D * sqrt(K); // we assume D is premultiplied by sqrt(sprungMass)
+               float ERP = (H * K) / (H * K + R);
+               float CFM = 1.0 / (H * K + R);
+               movedir[0] = CFM;
+               movedir[2] = ERP;
+       }
        if(jointtype == ed->priv.server->ode_joint_type && VectorCompare(origin, ed->priv.server->ode_joint_origin) && VectorCompare(velocity, ed->priv.server->ode_joint_velocity) && VectorCompare(angles, ed->priv.server->ode_joint_angles) && enemy == ed->priv.server->ode_joint_enemy && aiment == ed->priv.server->ode_joint_aiment && VectorCompare(movedir, ed->priv.server->ode_joint_movedir))
                return; // nothing to do
        AngleVectorsFLU(angles, forward, left, up);