verlet newb...

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