PhysicsShapeFriction shape,friction#

Parameters

shape - physics-shape handle returned by a shape command such as PhysicsBodyBox

friction# - Coulomb friction coefficient, 0 or higher; usually between 0 and 1

Description

Sets how strongly material slot 1 grips touching shapes. Slot 1 is also the shape's base material. Use PhysicsShapeMaterialFriction to edit another slot and PhysicsShapeGetFriction to read it. Edits wake affected enabled bodies and invalidate cached material sampling without changing mass.

Friction is what stops crates sliding down ramps and lets wheels bite. 0 is sheet ice, around 0.2 is polished floor, and values towards 1 grip like rubber. Every new shape starts at 0.6, a sensible general-purpose value.

The friction actually felt at a contact combines the two touching shapes' values, so an icy floor makes everything slide regardless of what lands on it. Tune the pair, not just one side.

Friction only fights sliding along surfaces - it does not slow bodies flying through the air. For that, see PhysicsBodyDamping.

Requires Extended mode.

See also: PhysicsShapeRestitution, PhysicsShapeFilter, PhysicsBodyDamping, PhysicsBodyBox.

Example

; PhysicsShapeFriction Example
; ----------------------------
; Requires Extended mode.

Graphics3D 640,480,0,2
SetBuffer BackBuffer()

Const PHYSICS_STATIC=0
Const PHYSICS_DYNAMIC=2

camera=CreateCamera()
PositionEntity camera,0,4,-6
RotateEntity camera,20,0,0

light=CreateLight()
RotateEntity light,45,-30,0
AmbientLight 50,50,50

world=CreatePhysicsWorld()
PhysicsGravity world,0,-9.81,0

; A long static runway for the crate to slide along
ground=CreateCube()
ScaleEntity ground,8,0.5,2
PositionEntity ground,0,-0.5,5,True
EntityColor ground,80,160,255
ground_body=CreatePhysicsBody(world,ground,PHYSICS_STATIC)
ground_shape=PhysicsBodyBox(ground_body,16,1,4,0)
PhysicsShapeFriction ground_shape,1

; The sliding crate whose friction we tune
crate=CreateCube()
ScaleEntity crate,0.4,0.4,0.4
PositionEntity crate,-5,0.4,5,True
EntityColor crate,255,120,70
crate_body=CreatePhysicsBody(world,crate,PHYSICS_DYNAMIC)
crate_shape=PhysicsBodyBox(crate_body,0.8,0.8,0.8,1)

friction#=0.5

While Not KeyDown(1)

    ; [ and ] tune the crate's friction coefficient
    If KeyDown(26) And friction>0 Then friction=friction-0.01
    If KeyDown(27) And friction<2 Then friction=friction+0.01
    If friction<0 Then friction=0

    ; Apply the current friction to the crate's shape
    PhysicsShapeFriction crate_shape,friction

    ; Space resets the crate and shoves it along the runway
    reset=0
    If KeyHit(57) Then reset=1
    If EntityY(crate,True)<-4 Then reset=1
    If reset
        FreePhysicsBody crate_body
        PositionEntity crate,-5,0.4,5,True
        RotateEntity crate,0,0,0
        crate_body=CreatePhysicsBody(world,crate,PHYSICS_DYNAMIC)
        crate_shape=PhysicsBodyBox(crate_body,0.8,0.8,0.8,1)
        PhysicsBodyImpulse crate_body,3,0,0
    EndIf

    StepPhysics world,1.0/60.0,4

    ; Arrow keys move the camera
    If KeyDown(200) Then MoveEntity camera,0,0,0.1
    If KeyDown(208) Then MoveEntity camera,0,0,-0.1
    If KeyDown(203) Then TurnEntity camera,0,1,0
    If KeyDown(205) Then TurnEntity camera,0,-1,0

    RenderWorld

    Text 0,0,"[ / ]: adjust friction   Space: shove the crate   Arrows: camera   Esc: exit"
    Text 0,20,"PhysicsShapeFriction crate_shape,"+friction
    Text 0,40,"Slide distance: "+(EntityX(crate,True)+5)+" m   (low friction slides further)"

    Flip

Wend

FreePhysicsWorld world
End

Index

Blitz3D+ Command Reference

PhysicsShapeFriction shape,friction#

Parameters

Description

Example