verlet newb...

I've been playing a bit with verlets lately, thanks to the simple code posted by Bot Builder in this thread: http://www.blitzbasic.com/Community/posts.php?topic=43242

I've picked at that code and altered variables so that I could better understand what was happening, Also removed some optimizations for the same reason... I think I finally am starting to get it, but I'm a bit stumped on adding collisions. edit: i've added code that properly detects collisions between verlets in different groups, but I need help on taking the proper action.

I'd like to see some really simple examples of how you would do this. I'd rather see simple examples than highly optimized at this point, since I am simply trying to understand things a bit better.

Anyways, here is where I am (again,... I take no credit for this code,... modified from Bot Builders) press space to add another box,... I'd like to have this code working with coliding boxes.

Thanks for any help.

Graphics 800,600,32,2

Type Verlet
 Field x#, y#, ox#, oy#, size,id , collide
End Type

Type Constraint
 Field Head.Verlet, Tail.Verlet, Length
End Type

Global circle=CreateImage (40,40)
SetBuffer ImageBuffer(circle)
Color 128,128,128
Oval 0,0,40,40
Color 0,255,0
Oval 0,0,40,40,0
MidHandle circle

Global circlehit=CreateImage (40,40)
SetBuffer ImageBuffer(circlehit)
Color 255,0,0
Oval 0,0,40,40
MidHandle circlehit

SetBuffer BackBuffer()

definebox() ; create a verlet box with constraints

While Not KeyHit(1)
	UpdateVerlets()
	Drawscreen()

	If MouseDown(1) Then ; use mouse to drag selected point around
		If selection.verlet<>Null Then
			selection\x=(selection\x+MouseX())/2
			selection\y=(selection\y+MouseY())/2
		Else
			For v.verlet=Each verlet
				If Sqr((MouseX()-v\x)*(MouseX()-v\x)+(MouseY()-v\y)*(MouseY()-v\y))<v\size Then
					selection=v
					Goto skipNull
				EndIf
			Next
			selection=Null
			.skipnull
		EndIf
	Else
		selection=Null
	EndIf

	Flip
	Cls
Wend

End 

Function UpdateVerlets()
	For v.Verlet=Each Verlet

		tx#=v\x	;tempx
		ty#=v\y	;tempy

		If v\collide = False 
			v\x=v\x+.99*(v\x-v\ox)	;give the verlet momentum from the previous loop - decay the value
			v\y=v\y+.99*(v\y-v\oy) ;+ .5	;same as above plus gravity
		EndIf 

		v\collide = False

		If v\x>GraphicsWidth()-v\size Then v\x=GraphicsWidth()-v\size ElseIf v\x<v\size Then v\x=v\size  ; constrain verlet to screen
		If v\y>GraphicsHeight()-v\size Then v\y=GraphicsHeight()-v\size ElseIf v\y<v\size Then v\y=v\size;

		v\ox=tx	; store verlet position in old slot for next loop
		v\oy=ty	;
	Next

	;basic collision detection,... needs to be integrated with code above
	For v.verlet = Each verlet
		For vv.verlet = Each verlet
			If v<>vv And v\id<>vv\id ; don't compare verlet against itself or others in the same id
				;v\collide = False
				;vv\collide = False
				dx#= v\x - vv\x
				dy#= v\y - vv\y
				dist# = Sqr (dx*dx + dy*dy)
				If dist# < 40
					;Text 50,50,"collide"
					v\collide = True
					vv\collide = true
				EndIf
			EndIf
		Next
	Next 
	
	For i=0 To 10		;Iterate
		For c.Constraint=Each Constraint
			dx#=c\Tail\x - c\Head\x 	;x vector distance
			dy#=c\Tail\y - c\Head\y 	;y vector distance
			dl#=Sqr(dx*dx+dy*dy)	;vector length
			d#=(dl - c\length) / Float(dl) ; vector length - constraint / vector length

			dx#=dx/2	; half distance
			dy#=dy/2	;half distance
			
			c\Head\x=c\Head\x+d*dx
			c\Head\y=c\Head\y+d*dy

			c\Tail\x=c\Tail\x-d*dx
			c\Tail\y=c\Tail\y-d*dy		;Simple, optimized rigid constraint algo

		Next
	Next
End Function

Function DrawScreen()
	For v.verlet=Each verlet
		If v\collide = False
			DrawImage circle,v\x,v\y	; draw red circle if colliding
		Else
			DrawImage circlehit,v\x,v\y	; draw image,... faster than circle below
		EndIf		
		;Oval v\x-v\size,v\y-v\size,v\size Shl 1,v\size Shl 1
	Next

	;For c.constraint = Each constraint ; draw all the constraints
	;	Line c\head\x,c\head\y,c\tail\x,c\tail\y
	;Next 
End Function

Function definebox()
For num = 1 To 4
	; define the shape and constraints
	; eventually replace with file/data statements and calculate constraint distance from initial point placement
	v1.verlet=New verlet
	v1\x=100 + (num*100)
	v1\y=100
	v1\ox=100+ (num*100)
	v1\oy=100
	v1\size=20
	v1\id=num
	
	v2.verlet = New verlet
	v2\x=150+ (num*100)
	v2\y=100
	v2\ox=150+ (num*100)
	v2\oy=100
	v2\size=20
	v2\id=num
	
	v3.verlet = New verlet
	v3\x=100+ (num*100)
	v3\y=150
	v3\ox=100+ (num*100)
	v3\oy=150
	v3\size=20
	v3\id=num
	
	v4.verlet = New verlet
	v4\x=150+ (num*100)
	v4\y=150
	v4\ox=150+ (num*100)
	v4\oy=150
	v4\size=20
	v4\id=num
	
	v5.verlet = New verlet
	v5\x=150+ (num*100)
	v5\y=200
	v5\ox=150+ (num*100)
	v5\oy=200
	v5\size=20
	v5\id=num
	
	v6.verlet = New verlet
	v6\x=150+ (num*100)
	v6\y=200
	v6\ox=150+ (num*100)
	v6\oy=200
	v6\size=20
	v6\id=num
	; now connect the verlets with constraints
	c.constraint=New constraint ;top
	c\Head=v1
	c\Tail=v2
	c\Length=50
	
	c.constraint=New constraint ;right
	c\Head=v2
	c\Tail=v4
	c\Length=50
	
	c.constraint=New constraint ;bottom
	c\Head=v3
	c\Tail=v4
	c\Length=50
	
	c.constraint = New constraint ;left
	c\Head=v3
	c\Tail=v1
	c\Length=50
	
	c.constraint = New constraint ; diagonal 1
	c\Head=v6
	c\Tail=v1
	c\Length=Sqr(100*100+(50*50))
	
	c.constraint = New constraint ; diagonal 2
	c\Head=v2
	c\Tail=v5
	c\Length=Sqr(100*100+(50*50))
	
	c.constraint = New constraint 
	c\Head=v4
	c\Tail=v6
	c\Length=50
	
	c.constraint=New constraint ;right
	c\Head=v5
	c\Tail=v6
	c\Length=50
	
	c.constraint=New constraint ;bottom
	c\Head=v3
	c\Tail=v5
	c\Length=50
	
	c.constraint = New constraint ;
	c\Head=v3
	c\Tail=v6
	c\Length=Sqr(50*50+(50*50))
	
	c.constraint = New constraint ; 
	c\Head=v4
	c\Tail=v1
	c\Length=Sqr(50*50+(50*50))
Next 
End Function  

I want to see stuff too

This post is mainly aimed at BotBuilder, Sswift, Bouncer, Dev, Miracle and Frank Taylor but any responses are welcome.

Sorry to ressurect this old post, but I have been playing about with Verlet integration and constraints for the past week and dont seem to be getting any closer to making a fully working 3D ragdoll. After searching through the forums I noticed that BotBuilder, Sswift, Bouncer, Dev, Miracle and Frank Taylor had all looked into this topic in some depth a year or two ago, unfortunately most of the posts just died off without resolving some major issues and a lot of the links to files are dead.

So what I am asking is :-

1. Can 3D ragdoll be accomplihed in Blitz3d without ODE etc
2. Has anybody got any code examples of a 3D system that they dont mind sharing.
3. Have the problems with angular constraints been overcome.
4. Has the problems with collisions been overcome.
5. Has anybody got any code (3d or 2d verlet integration/constraints) with all the unneccessary garbage cleared out ie. supercams, lensflares etc so that i can learn this system better (Im not just a Verlet Newbie I'm also a Blitz Newbie).
6. Is the system fast enough to be used in games. Some of the demos I tried, bouncers for example was very fast whilst others crawled.

I know what some people are going to reply, "if your a newbie, you should be creating programs like, HELLO WORLD, and rotating primitives. I admit I am new to Blitz3D but have been hobby programming since the days of the ZX81, and now i've got my teeth into this im not gonna let go until I've cracked it or it cracks me.

Paul

1. sure.
2. sorry
3. what problems? Angular constraits are just two regular constraints+another constraint that keeps it in certain angle ranges. I suppose this allows free movement within that range though, which you might not want.
4. Well, not really this is the main problem.
5. The code above is pretty simple although prolly not commented enough
6. Yes. Hitman 2 uses verlet.

Thanks for the reply BotBuilder, but unfortunately your replies have created more questions than answers(not that I dont appreciate your response).

In my naiveity, with regards to collisions I thought I could just use the entity (b3d model) that the pivots/constraints were attached to, to perform collision checking.

The reason why I asked question 1 and 6 regarding was it possible to create a ragdoll system in Blitz3d and was it fast enough was because, I have'nt seen any 3d demos that dont you Tokamak/ODE.

Another plea to anybody who has any "cleaned up" 3d ragdoll code, that they dont mind sharing, can you please post.

Paul

Nexus,

I've got a couple of ragdoll demos at home - done completely in Blitz. I've no idea who wrote them, how good they are or how tidy the code is but if you e-mail me I'll send on the files.

E-mail .... stevie(AT)steviegoodwin.plus.com

Stevie

Thanks for the email Stevie, the attached ragdoll programs was certainly a different approach than the other methods I've seen. Its given me some idea's.

Thanks again.

paul