Strings / Ropes, Etc.

Hey All,

I'm working on a rope / string simulation based on hugo elias's model for a string, found here...

[link]http://freespace.virgin.net/hugo.elias/models/m_string.htm[/link]

It seems to be working o.k., but there are a few things about it which i don't like, mainly the fact that it seems to continuously relax from gravity. It also is a little bit too flexible. Does anyone have any ideas for improvement, or other models?

thanks,

Roland

Graphics3D 640,480,0,2
Global cam = CreateCamera()

PositionEntity cam,0,10,-40
l=CreateLight()


Type Node
	Field entity
	Field x#
	Field y#
	Field xspeed#
	Field yspeed#
	Field num
	Field newx#
	Field newy#
	Field dragging
End Type

Global gravity# = -.15
Global damping# = .9
Global length# = 2
Global endnode
Global startnode

Global mag1#
Global mag2#
Global extension1#
Global extension2#
Global xvector1#
Global xvector2#
Global yvector1#
Global yvector2#
Global xv#
Global yv#

Global picker = CreateCube()
ScaleEntity picker,100,100,.2
EntityAlpha picker,.2
EntityPickMode picker,2


For x=0 To 31

	n.Node = New Node
	n\entity = CreateSphere(3)
	ScaleEntity n\entity,.75,.75,.75
	n\x = 0
	n\y = Float(x)
	n\num = x
	
	PositionEntity n\entity,n\x,n\y,0
	
	If x = 0 Then endnode = Handle(n)
	
	If x = 31 Then startnode = Handle(n)
	
	EntityPickMode n\entity,2

Next



While Not KeyHit(1)


	updatenodes()

	If MouseHit(1)
		CameraPick cam,MouseX(),MouseY()
		For n.Node = Each Node
		
			If PickedEntity() = n\entity
				n\dragging = 1
				EntityColor n\entity,255,0,0
			Else
				n\dragging = 0
				EntityColor n\entity,255,255,255
			EndIf
		Next
	EndIf
	
	If MouseDown(1)
		CameraPick cam,MouseX(),MouseY()
		For n.Node = Each Node
			If n\dragging = 1
				n\x = PickedX()
				n\y = PickedY()
			EndIf
		
		Next
	EndIf



UpdateWorld
 
RenderWorld

n.Node = First Node
Text 0,0,n\x

Flip



Wend


End


Function dist#(xlen#,ylen#)

	Return Sqr((xlen^2)+(ylen^2))


End Function



Function updatenodes()

	For n.Node = Each Node
	
		hasno1 = 0
		hasno2 = 0
	
		For no.Node = Each Node
		
			If (no\num = n\num-1)
			
				xvector1 = no\x-n\x
				yvector1 = no\y-n\y
				mag1 = dist#(xvector1,yvector1)
				extension1 = mag1-length
			
				hasno1 = 1
			
			Else If (no\num = n\num+1)
	
				xvector2 = no\x-n\x
				yvector2 = no\y-n\y
				mag2 = dist#(xvector2,yvector2)
				extension2 = mag2-length
				hasno2 = 1
			
			EndIf
		
		Next
		
		If hasno1 <> 1
		
			xvector1 = 0
			yvector1 = 0
			mag1 = 1
			extension1 = 0			
		
		EndIf

		If hasno2 <> 1
		
			xvector2 = 0
			yvector2 = 0
			mag2 = 1
			extension2 = 0			
		
		EndIf

		
		xv = (xvector1/mag1*extension1)+(xvector2/mag2*extension2)	

		yv = (yvector1/mag1*extension1)+(yvector2/mag2*extension2)+gravity
		
		n\xspeed = n\xspeed*damping+(xv*.07)
		n\yspeed = n\yspeed*damping+(yv*.07)

		n\newx = n\x+n\xspeed
		n\newy = n\y+n\yspeed

		If Handle(n) = startnode
			n\newx = 0
			n\newy = 31
		EndIf

		
	Next


	For n.Node = Each Node
		
		n\x = n\newx
		n\y = n\newy
		

		
		If Handle(n) = startnode
			n\x = 0
			n\y = 31
		EndIf
		
		PositionEntity n\entity,n\x,n\y,0	
	
	Next


End Function