Tutorial: How to create physics joints in SP simulation

MrDailyBlah

Hi there..
Now probably all of u guyz have used Sketchyphysics at some point, and created physics joints in them.

The problem though, is that sumtimes the joints become glitchy : they either become floppy or fall off completely... not good...

The solution to the problem is to create a joint while the simulation is running.

Ever explored the scripts which make up Sketchyphysics? If so, u've probably seen the module "NewtonServer" sumwhere... . this module is just about the kernel of the Sketchyphysics system. It creates nearly every physical feature of Sketchyphysics, from joints to forces to gravity and so on.

We need one of its methods, which is "createJoint"...


# this example creates a hinge joint
parent={grp} # a grouped object that encases the joint
child={grp} # a grouped object that is attached to the joint

type="hinge"
min=0
max=0
accel=0
damp=0
breakingForce=1000000
limits=[min,max,accel,damp,0,0,breakingForce] # parameters for the joint

xform=parent.transformation
pinDir=xform.zaxis.to_a # the axis of the joint

parentBody=DL;;PtrData.new(parent.get_attribute("SPOBJ","body",nil)) # converted parent body

childBody=DL;;PtrData.new(child.get_attribute("SPOBJ","body",nil)) # converted child body

  jnt=NewtonServer.createJoint(type,xform.origin.to_a.pack("f*"),
            pinDir.pack("f*"),
            childBody,parentBody, 
            limits.pack("f*") ) # the joint itself

Important: in general, all array objects need ".pack("f*")" after them, and all grouped bodies need to be converted into DL::PtrData (by using "DL::PtrData.new({grp}.get_attribute("SPOBJ","body",nil))" )

The created joint doesnt have the bugs normal joints have. (hopefully... )

Have fun "Sketchyphysic"ing (!)