Stretchy bones shiver

["Matthew Lowery" <Matt(at)luma.co.za>]

Hay gang,

 

I've got this stretchy bone set up, run the script below to see what I mean.

 

Create2DSkeleton -4, -3.74915180455534E-29, 0, -1, 1.224606353822E-16, -2, -90, 33.6900675259798, 2.33882585463089E-15, 4

AppendBone "eff", 3, 1.224606353822E-16, -2

AppendBone "eff", 6, -3.74915180455534E-29, 0

ActivateObjectSelTool

ActivateObjectSelTool

DeselectAll

GetPrim "Cube"

SetValue "cube.cube.length", 2

MatchTransform "cube", "eff", siTrn

SelectObj "eff", , True

ApplyCns "Position", "eff", "cube"

SelectObj "bone", , True

AddExpr "bone.bone.length"

SetExpr "bone.bone.length", "cond( ctr_dist( root. , cube. ) > 10.818 , ctr_dist( root. , cube. ) / 3 , 3.605551 )"

CopyAnimation "bone.bone.length", True, True, False

SelectObj "bone1", , True

PasteAnimation "bone1.bone.length"

SelectObj "bone2", , True

PasteAnimation "bone2.bone.length"

SelectObj "cube", , True

 

So if you move the implicit cube around the bone stretches.... good.

Now the problem is that the bones shiver slightly. Move the Implicit cube slowly and look at the scene from the top view to see what I mean.

 

It seems to happen because softimage is only evaluating the distance between the cube and root object down to the third decimal place. i.e. 10.574 units, as opposed to 10.5747895 units so the effector doesn't reach it's target cube all the time.

 

Does anyone have a better way of building stretchy bones? Or alternatively know how I can get xsi to measure accurately down to like the sixth or seventh decimal place?

 

Thanks,

m(at)

 

P.S. I'm still running xsi 4.2 :(