Global things:TList=New TList
Type thing
	Field x#,y#,vx#,vy#,r#,m#,ox#,oy#
	Field x2#,y2#,vx2#,vy2#
	Field cor#,cof#	'coefficient of restitution, friction
	Field an#,van#
	Field col#
	
	Method New()
		things.addlast Self
		m=1
		r=1
		cor=1
		cof=0
		col=Rand(360)
	End Method
	
	Function Create:thing(x#,y#,m#,r#,cor#,cof#)
		t:thing=New thing
		t.x2=x
		t.y2=y
		t.m=m
		t.r=r
		t.cor=cor
		t.cof=cof
		Return t
	End Function
	
	Method checkcollide(t:thing)
	
		'quick bounding box check
		If Not (x-r<t.x+t.r And x+r>t.x-t.r And y-r<t.y+t.r And y+r>t.y-t.r)
			Return False
		EndIf

		'find difference between new positions
		dx#=x-t.x
		dy#=y-t.y
		d#=dx*dx+dy*dy
		tr#=r+t.r
		
		If d=0 Return False
		
		'if radii overlap
		If d<tr*tr
		
			'find difference in old positions
			odx#=ox-t.ox
			ody#=oy-t.oy
			dvx#=vx-t.vx
			dvy#=vy-t.vy
			
			'find time of collision
			a#=dvx*dvx+dvy*dvy
			b#=2*dvx*odx+2*dvy*ody
			c#=odx*odx+ody*ody-tr*tr
			If a=0 Return False
			If (b*b-4*a*c)<0 Return False
			time#=(-b-Sqr(b*b-4*a*c))/(2*a)
			
			If time<0 time=(-b+Sqr(b*b-4*a*c))/(2*a)
			If Abs(time)>1	'something mad has gone on, such as both objects beginning the frame overlapping
				d=Sqr(d)
				diff#=tr-d
				dx:/d
				dy:/d
				f#=diff*t.m/(m+t.m)
				f2#=diff*m/(m+t.m)
				mx#=dx*f
				my#=dy*f
				mx2#=-dx*f2
				my2#=-dy*f2
				x2:+mx
				y2:+my
				vx2:+mx
				vy2:+my
				t.x2:+mx2
				t.y2:+my2
				t.vx2:+mx2
				t.vy2:+my2
				Return True
			EndIf
			
			'find positions of objects at time of collision
			nx#=ox+time*vx
			ny#=oy+time*vy
			nx2#=t.ox+time*t.vx
			ny2#=t.oy+time*t.vy
			
			'find vector between objects at collision
			dx=nx-nx2
			dy=ny-ny2
			d=tr
			
			
			If d=0 Return False	'just in case#
			dx:/d
			dy:/d
			
			'work out COR of collision (guess)
			rcor#=(m*cor+t.m*t.cor)/(m+t.m)
			
			'find components of velocity towards collision normal and tangential
			in#=vx*dx+vy*dy
			in2#=t.vx*dx+t.vy*dy
			n#=-vx*dy+vy*dx
			n2#=-t.vx*dy+t.vy*dx
			
			'find new velocities in direction of normal after collision
			nin#=(m*in+t.m*in2+t.m*rcor*(in2-in))/(m+t.m)
			nin2#=(m*in+t.m*in2+m*rcor*(in-in2))/(m+t.m)
			
			Rem
			'work out friction and apply to tangential velocity
			rcof#=(cof+t.cof)/(m+t.m)
			rcof=0
			f#=(in2-in)*rcof
			nn#=-Sgn(n)*f/m
			nn:+n
			If nn*n<0 nn=0
			
			nn2#=-Sgn(n2)*f/t.m
			nn2:+n2
			If nn2*n2<0 nn2=0
			EndRem
			
			'combine to give new velocities
			nvx#=nin*dx-n*dy
			nvy#=nin*dy+n*dx
			
			nvx2#=nin2*dx-n2*dy
			nvy2#=nin2*dy+n2*dx
			
			'add remaining time's movement using new velocities
			nx:+(1-time)*nvx
			ny:+(1-time)*nvy
			nx2:+(1-time)*nvx2
			ny2:+(1-time)*nvy2
			
			
			'DEBUG
			dx=nx-x
			dy=ny-y
			If dx*dx+dy*dy>50
			'	DebugStop
			'	Print "WOW"+(dx*dx+dy*dy)
			'	DrawLine t.x,t.y,x,y
			EndIf
			
			x2:+nx-x
			y2:+ny-y
			vx2:+nvx-vx
			vy2:+nvy-vy
			
			t.x2:+nx2-t.x
			t.y2:+ny2-t.y
			t.vx2:+nvx2-t.vx
			t.vy2:+nvy2-t.vy
			
			Rem
			x=nx
			y=ny
			t.x=nx2
			t.y=ny2
			vx=nvx
			vy=nvy
			t.vx=nvx2
			t.vy=nvy2
			EndRem
			
			Return True
		EndIf
	End Method
	
	Method update()
	
		x=x2
		y=y2
		vx=vx2
		vy=vy2
		
	
		ox=x
		oy=y
		x:+vx
		y:+vy
		If x<r
			time#=(r-ox)/vx
			vx=-vx*cor
			x=r+(1-time)*vx
		EndIf
		If x>600-r
			time#=(600-r-ox)/vx
			vx=-vx*cor
			x=600-r+(1-time)*vx
		EndIf
		If y<r
			time#=(r-oy)/vy
			vy=-vy*cor
			y=r+(1-time)*vy
		EndIf
		If y>600-r
			time#=(600-r-oy)/vy
			vy=-vy*cor
			y=600-r+(1-time)*vy
		EndIf
		
		x2=x
		y2=y
		vx2=vx
		vy2=vy
	End Method
	
	Method draw()
		col:+.5
		SetColor Sin(col)*100+100,Cos(col*2)*100+100,Cos(col*3)*100+100

		SetAlpha .8
		'SetBlend lightblend
		DrawOval x-r,y-r,r*2,r*2
		'DrawLine x,y,x+vx*10,y+vy*10
		
		'SetBlend shadeblend
		SetAlpha .1
		DrawRect x-r*10,y-r*10,r*20,r*20
	End Method
End Type

Global me:thing
Function setup()
	things=New TList
	me:thing=thing.Create(100,40,3,30,.5,0)
	me.vy2=1
	me.vx2=1
	'thing.Create(300,300,9,30,.5,0)
	thing.Create(100,500,4,20,.5,0)
	
	For c=1 To 100
		makething
	Next
	
End Function

Function makething()
	in=1
	While in
		pr=Rand(50,250)
		an=Rand(360)
		x=Cos(an)*pr+300
		y=Sin(an)*pr+300
		in=0
		r=Rnd(5,10)
		For t:thing=EachIn things
			dx#=x-t.x
			dy#=y-t.y
			d#=dx*dx+dy*dy
			If d<=(t.r+r)*(t.r+r)
				in=1
				Exit
			EndIf
		Next
	Wend
	thing.Create(x,y,.01*r,r,.5,.5)
End Function

AppTitle="some old ones"
Graphics 600,600,0
SetBlend ALPHABLEND
'SetClsColor 255,255,255
setup

While Not (KeyHit(KEY_ESCAPE) Or AppTerminate())
	If KeyHit(KEY_SPACE) setup
	
	If Rand(50)=1
		'makething
	EndIf

	me.vx2:+(KeyDown(KEY_RIGHT)-KeyDown(KEY_LEFT))*.1
	'me.vy:+(KeyDown(KEY_RIGHT)-KeyDown(KEY_LEFT))*.1
	me.vy2:+(KeyDown(KEY_DOWN)-KeyDown(KEY_UP))*.1

	e#=0
	For t:thing=EachIn things
		t.update
		te#=0.5*t.m*(t.vx*t.vx+t.vy*t.vy)
		'DrawText te,t.x,t.y
		e#:+te
	Next
	DrawText e,0,15
	
	
	collision=10
	'While collision>0
		ts:TList=things.copy()
		While ts.count()>1
			t:thing=thing(ts.removefirst())
			For t2:thing=EachIn ts
				If t.checkcollide(t2)
					collision:-1
				Else
					collision=0
				EndIf
			Next
		Wend
	'Wend
	
	ts=things.copy()
	While ts.count()>1
		t:thing=thing(ts.removefirst())
		For t2:thing=EachIn ts
			dx#=t2.x-t.x
			dy#=t2.y-t.y
			d#=Sqr(dx*dx+dy*dy)
			If d<>0
				f#=5/(d*d)
				t.vx2:+t2.m*f*dx/d
				t.vy2:+t2.m*f*dy/d
				t2.vx2:-t.m*f*dx/d
				t2.vy2:-t.m*f*dy/d
			EndIf
		Next
	Wend
		
	For t:thing=EachIn things
		t.draw
	Next
	
	DrawText things.count(),0,0

	Flip
	Cls
Wend