[bb] Simple 3D sphere-to-sphere physics by Ken Lynch [ 1+ years ago ]

BlitzBot · June 29, 2017, 00:28:39

Title : Simple 3D sphere-to-sphere physics
Author : Ken Lynch
Posted : 1+ years ago

Description : This is an example of how to do simple physics using sphere-to-sphere type collisions. It uses LinePick instead of the standard collision method as it offers more control and encapsulates everything you need in simple functions that you can use in your own code with little or no modification.

Hope you find it useful.

Code :

Code (blitzbasic) Select

;
; Simple 3D collision with physics
;

;
; Data types
;

Type PhysicsEntity
	Field entity%
	Field radius#, mass#, bounce#, friction#
	Field x#, y#, z#
	Field xv#, yv#, zv#
End Type

;
; The usual stuff
;

Graphics3D 800, 600

light = CreateLight()

camera = CreateCamera()
PositionEntity camera, 0, 0, -25

;
; Create our entities
;
For i = -8 To 8 Step 2
	For j = -8 To 8 Step 2
		ent = CreateSphere()
		ScaleEntity ent, 0.5, 0.5, 0.5
		PositionEntity ent, i, j, 0
		SetEntityPhysics ent, 0.5, 1, 0.90, 0.0005
		ApplyForce ent, Rnd(-0.2, 0.2), Rnd(-0.2, 0.2), 0
	Next
Next

;
; Main loop
;
Repeat
	UpdatePhysics
	RenderWorld
	Flip
Until KeyHit(1)

;
; Physics handling functions
;

;
; FindPhysicsEntity(entity)
;
; Quickly find PhysicsEntity data type from entity using the Handle stored in EntityName
;
Function FindPhysicsEntity.PhysicsEntity(entity)
	name = EntityName(entity)
	Return Object.PhysicsEntity(name)
End Function

;
; SetEntityPhysics entity,radius#,mass#
;
; Sets an entity's phisics properties
;
Function SetEntityPhysics(entity, radius#=1, mass#=1, bounce#=1, friction#=0)
	pe.PhysicsEntity = New PhysicsEntity
	peentity = entity
	peadius = radius
	pemass = mass
	peounce = bounce
	pefriction = friction
	EntityRadius entity, radius
	EntityPickMode entity, 1
	;
	; Magic to store the Handle of pe in the entity's name
	;
	NameEntity entity, Handle(pe)
End Function

;
; RemoveEntityPhysics entity
;
; Removes an entity's physics properties
;
Function RemoveEntityPhysics(entity)
	pe.PhysicsEntity = FindPhysicsEntity(entity)
	If pe <> Null Then
		NameEntity entity, ""
		Delete pe
	Else
		RuntimeError "Entity has no physics"
	End If
End Function

;
; ApplyForce entity,x#,y#,z#
;
; Applies an impulse force to physics entity
;
Function ApplyForce(entity, x#, y#, z#)
	pe.PhysicsEntity = FindPhysicsEntity(entity)
	If pe <> Null Then
		pexv = pexv + x
		peyv = peyv + y
		pezv = pezv + z
	Else
		RuntimeError "Entity has no physics"
	End If
End Function

;
; UpdatePhysics
;
; This will update all entities with physics
;

Function UpdatePhysics()
	For e1.PhysicsEntity = Each PhysicsEntity
		;
		; Check if the entity is moving
		;
		If e1xv <> 0 Or e1yv <> 0 Or e1zv <> 0 Then
	
			;
			; Record current entity position
			;
			x# = EntityX(e1entity, True)
			y# = EntityY(e1entity, True)
			z# = EntityZ(e1entity, True)	
	
			;
			; Reduce velocity due to friction
			;
			If e1friction > 0 Then
				speed# = Sqr(e1xv ^ 2 + e1yv ^ 2 + e1zv ^ 2)
				new_speed# = speed - e1friction
				If new_speed <= 0 Then
					e1xv = 0
					e1yv = 0
					e1zv = 0
				Else
					e1xv = e1xv / speed * new_speed
					e1yv = e1yv / speed * new_speed
					e1zv = e1zv / speed * new_speed
				End If
			End If

			;
			; Do a line pick to check for collisions
			;
			ent = LinePick(x, y, z, e1xv, e1yv, e1zv, e1adius)
			If ent > 0 Then e2.PhysicsEntity = FindPhysicsEntity(ent)
			If ent = 0 Or e2 = Null
				;
				; Add velocity vector to current position
				;
				x = x + e1xv
				y = y + e1yv
				z = z + e1zv
			Else
				;
				; Get the point of collision
				;
				Px# = PickedX()
				Py# = PickedY()
				Pz# = PickedZ()
			
				;
				; Get the collision normal vector
				;
				Nx# = PickedNX()
				Ny# = PickedNY()
				Nz# = PickedNZ()
			
				;
				; Back up a little to prevent collision errors
				;
				TFormNormal e1xv, e1yv, e1zv, 0, 0
				dx# = TFormedX() * 0.05
				dy# = TFormedY() * 0.05
				dz# = TFormedZ() * 0.05
						
				;
				; Calculate the new position
				;
				x = Px + (e1adius) * Nx - dx
				y = Py + (e1adius) * Ny - dy
				z = Pz + (e1adius) * Nz - dz
			
				;
				; Conservation of momentum
				;
				a1# = e1xv * Nx + e1yv * Ny + e1zv * Nz
				a2# = e2xv * Nx + e2yv * Ny + e2zv * Nz
				OptP# = 2 * (a1 - a2) / (e1mass + e2mass)
			
				e1xv = (e1xv - (OptP * e2mass * Nx)) * e1ounce
				e1yv = (e1yv - (OptP * e2mass * Ny)) * e1ounce
				e1zv = (e1zv - (OptP * e2mass * Nz)) * e1ounce

				e2xv = (e2xv + (OptP * e1mass * Nx)) * e2ounce
				e2yv = (e2yv + (OptP * e1mass * Ny)) * e2ounce
				e2zv = (e2zv + (OptP * e1mass * Nz)) * e2ounce
			End If
			;
			; Reposition entity
			;
			PositionEntity e1entity, x, y, z, True
		End If
	Next
End Function

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[bb] Simple 3D sphere-to-sphere physics by Ken Lynch [ 1+ years ago ]

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