Verlets are simply a system of doing physics that work by linking several points with constraints. Each loop through the constraints are satisfied several times.
There is a good explanation of how things work here:
http://www.gamasutra.com/resource_guide/20030121/jacobson_01.shtml
Here is a simple b3d example
There is a good explanation of how things work here:
http://www.gamasutra.com/resource_guide/20030121/jacobson_01.shtml
Here is a simple b3d example
Open in online IDEGlobal screen_w = 1024 Global screen_h = 768 Global gravity# = .25 Graphics3D screen_w,screen_h,0,2 SetBuffer BackBuffer() SeedRnd MilliSecs() timer = CreateTimer (60) ; lock game fps to this Type vector3 Field x# Field y# Field z# End Type Type Verlet Field pos.vector3 ; verlet position Field vel.vector3 ; verlet velocity Field old.vector3 ; store the previous pos here Field radius ; size of verlet Field id ;use to identify groups Field collide ; is this colliding? Field pivot ; pivot for operations End Type Type constraint Field p1.verlet Field p2.verlet Field length# Field mesh ; display line End Type campivot = CreatePivot() cam = CreateCamera(campivot) CameraZoom cam,2 MoveEntity cam,0,200,500 PointEntity cam,campivot light = CreateLight() ;PositionEntity light,0,100,-50 RotateEntity light,90,0,0 Global arenabounds = 200 wall1 = CreateCube() PositionEntity wall1,-arenabounds,0,0 ScaleEntity wall1,1,1,arenabounds wall2 = CreateCube() PositionEntity wall2,arenabounds,0,0 ScaleEntity wall2,1,1,arenabounds wall3 = CreateCube() PositionEntity wall3,0,0,arenabounds ScaleEntity wall3,arenabounds,1,1 wall4 = CreateCube() PositionEntity wall4,0,0,-arenabounds ScaleEntity wall4,arenabounds,1,1 ground = CreatePlane() EntityColor ground,32,32,64 EntityAlpha ground, .9 mirror = CreateMirror() definePyramid() ;CreateVerlet.verlet (xpos,ypos,size,id) Global v1.verlet = CreateVerlet (10,0,10,8,1) Global v2.verlet = CreateVerlet(10,0,-10,8,1) Global v3.verlet = CreateVerlet (-10,0,10,8,1) Global v4.verlet = CreateVerlet(-10,0,-10,8,1) Global v5.verlet = CreateVerlet(0,20,0,8,1) ConstrainVerlet (v1,v2) ConstrainVerlet(v2,v3) ConstrainVerlet(v1,v3) ConstrainVerlet(v1,v4) ConstrainVerlet(v2,v4) ConstrainVerlet(v3,v4) ConstrainVerlet(v1,v5) ConstrainVerlet(v2,v5) ConstrainVerlet(v3,v5) ConstrainVerlet(v4,v5) EntityColor v1\pivot,160,32,32 While Not KeyHit(1) WaitTimer(Timer) ; Pause until the timer reaches 60 (caps the game framerate on faster systems) ; move verlet 1 based on arrow keys v1\pos\z = v1\pos\z + (KeyDown(208) - KeyDown(200) ) * .8 v1\pos\x = v1\pos\x + (KeyDown(203) - KeyDown(205) ) * .8 v1\pos\y = v1\pos\y + KeyDown(57) * 2 UpdateVerlets() UpdateConstraints() positionstuff() UpdateWorld() RenderWorld() Text 20,20,"use arrow keys and space bar to move verlet cage" Flip() Cls() Wend End Function definePyramid() ;CreateVerlet.verlet (xpos,ypos,size,id) v11.verlet = CreateVerlet (10,20,10,8,2) v12.verlet = CreateVerlet(10,20,-10,8,2) v13.verlet = CreateVerlet (-10,20,10,8,2) v14.verlet = CreateVerlet(-10,20,-10,8,2) v15.verlet = CreateVerlet(0,40,0,8,2) ConstrainVerlet (v11,v12) ConstrainVerlet(v12,v13) ConstrainVerlet(v11,v13) ConstrainVerlet(v11,v14) ConstrainVerlet(v12,v14) ConstrainVerlet(v13,v14) ConstrainVerlet(v11,v15) ConstrainVerlet(v12,v15) ConstrainVerlet(v13,v15) ConstrainVerlet(v14,v15) End Function Function CreateVerlet.verlet (xpos,ypos,zpos,size,id) v.verlet=New verlet v\pos = New vector3 v\pos\x = xpos v\pos\y = ypos v\pos\z = zpos v\vel = New vector3 v\vel\x = 0 v\vel\y = 0 v\vel\z = 0 v\old = New vector3 v\old\x = xpos v\old\y = ypos v\old\z = zpos v\radius = size v\id = id v\pivot = CreateSphere() ScaleEntity v\pivot,size,size,size Return v End Function Function ConstrainVerlet.constraint (head.verlet, tail.verlet) Local dx#,dy#,dz# ;this creates a new constraint and sets the length equal to the current distance between the verlets c.constraint = New constraint c\p1.verlet = head.verlet c\p2.verlet = tail.verlet dx = c\p1\pos\x - c\p2\pos\x dy = c\p1\pos\y - c\p2\pos\y dz = c\p1\pos\z - c\p2\pos\z c\length = Sqr ( dx*dx + dy*dy + dz*dz ) c\mesh = CreateCube() ScaleEntity c\mesh,.2,.2,c\length * .5 PositionMesh c\mesh,0,0,1 ;DebugLog c\length Return c End Function Function UpdateVerlets() Local dx#,dy#,dz#,dist# For v.verlet = Each verlet v\collide = False v\vel\x = (v\pos\x - v\old\x)*.985 ; Get the velocities of the verlet,...add a bit of decay to simulate friction v\vel\y = (v\pos\y - v\old\y)*.985 v\vel\z = (v\pos\z - v\old\z)*.985 v\old\x = v\pos\x ; store position in "old" v\old\y = v\pos\y v\old\z = v\pos\z v\pos\x = v\pos\x + v\vel\x ;store new postion based on velocity v\pos\y = v\pos\y + v\vel\y - gravity v\pos\z = v\pos\z + v\vel\z For vv.verlet = Each verlet If v <> vv And v\id <> vv\id; if not the same verlet or group dx = v\pos\x - vv\pos\x dy = v\pos\y - vv\pos\y dz = v\pos\z - vv\pos\z dist = Sqr ( dx*dx + dy*dy + dz*dz) TotalRadius# = v\radius + vv\radius If dist < Totalradius Diffx# = ( dist - TotalRadius ) * ( dx / dist ) Diffy# = ( dist - TotalRadius ) * ( dy / dist ) Diffz# = ( dist - TotalRadius ) * ( dz / dist ) v\pos\x = v\pos\x - Diffx ;* .5 v\pos\y = v\pos\y - Diffy ;* .5 v\pos\z = v\pos\z - Diffz ;* .5 vv\pos\x = vv\pos\x + Diffx ;* .5 vv\pos\y = vv\pos\y + Diffy ;* .5 vv\pos\z = vv\pos\z - Diffz ;* .5 v\collide = True EndIf EndIf Next ;check screen bounds If v\pos\y < v\radius ;ground collision v\pos\y= v\radius v\collide = True EndIf If v\pos\x >arenabounds Then v\pos\x = arenabounds If v\pos\x < -arenabounds Then v\pos\x = -arenabounds If v\pos\z >arenabounds Then v\pos\z = arenabounds If v\pos\z < -arenabounds Then v\pos\z = -arenabounds Next End Function Function UpdateConstraints() Local dx#,dy#,dz#,length#,diff# For loop = 1 To 5 ;iterations For c.constraint = Each constraint dx=c\p2\pos\x - c\p1\pos\x dy=c\p2\pos\y - c\p1\pos\y dz=c\p2\pos\z - c\p1\pos\z length=Sqr(dx*dx + dy*dy + dz*dz) ; distance between p1 and p2 If length<>0 ;avoid divide by 0, then normalize the vector diff = (length - c\length) / length ; vector length minus constraint length EndIf dx = dx * .5 ;find the midpoint dy = dy * .5 dz = dz * .5 c\p1\pos\x = c\p1\pos\x + diff * dx c\p1\pos\y = c\p1\pos\y + diff * dy c\p1\pos\z = c\p1\pos\z + diff * dz c\p2\pos\x = c\p2\pos\x - diff * dx c\p2\pos\y = c\p2\pos\y - diff * dy c\p2\pos\z = c\p2\pos\z - diff * dz Next ;constraints Next ;iterations End Function Function positionstuff() For v.verlet = Each verlet EntityColor v\pivot,255,255,255 If v\collide = True Then EntityColor v\pivot,128,0,0 PositionEntity v\pivot, v\pos\x, v\pos\y, v\pos\z Next For c.constraint = Each constraint PositionEntity c\mesh, c\p1\pos\x, c\p1\pos\y, c\p1\pos\z PointEntity c\mesh ,c\p2\pivot Next End Function