Blitz3D+ Command Reference

CollisionTime# ( entity,collision_index )

Parameters

entity - entity handle
collision_index - index of the collision, from 1 to CountCollisions( entity )

Description

Returns how far through its movement an entity got before a collision, as a fraction from 0 to 1.

Despite the name this is not a duration - it is a position along the movement the entity made during the UpdateWorld that recorded collision number collision_index. 0 means the entity collided the moment it started moving, 0.5 halfway through its step, values near 1 right at the end.

Multiply it by the distance the entity tried to move that frame to get the distance actually travelled before contact - useful for judging impact strength, or for placing an effect part-way along a fast projectile's path.

In debug mode an index outside 1...CountCollisions( entity ) is a runtime error.

See also: CountCollisions, CollisionX, CollisionNX, CollisionEntity, UpdateWorld.

Example

; CollisionTime Example
; ---------------------

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

; Collision type ids
type_player=1
type_scenery=2

; NOTE: fixed overhead camera - the arrow keys steer the PLAYER, not the camera
camera=CreateCamera()
PositionEntity camera,0,13,-13
RotateEntity camera,45,0,0

light=CreateLight()
RotateEntity light,60,30,0

floor=CreatePlane()
EntityColor floor,70,110,70

; The player ball is the collision SOURCE, so it needs an ellipsoid radius
player=CreateSphere()
EntityColor player,220,60,60
PositionEntity player,0,1,0
EntityRadius player,1
EntityType player,type_player

; Two walls meeting in a corner, plus a crate
wall1=CreateCube()
ScaleEntity wall1,7,1.5,0.5
PositionEntity wall1,0,1.5,7
EntityColor wall1,150,150,160
EntityType wall1,type_scenery

wall2=CreateCube()
ScaleEntity wall2,0.5,1.5,7
PositionEntity wall2,7,1.5,0
EntityColor wall2,150,150,160
EntityType wall2,type_scenery

crate=CreateCube()
ScaleEntity crate,1.2,1.2,1.2
PositionEntity crate,-4,1.2,3
EntityColor crate,200,160,60
EntityType crate,type_scenery

; Ellipsoid-to-polygon collisions with a sliding response
Collisions type_player,type_scenery,2,2

While Not KeyDown(1)

    ; Arrow keys steer the player ball
    If KeyDown(200) Then MoveEntity player,0,0,0.1
    If KeyDown(208) Then MoveEntity player,0,0,-0.1
    If KeyDown(203) Then MoveEntity player,-0.1,0,0
    If KeyDown(205) Then MoveEntity player,0.1,0,0

    ; UpdateWorld performs the collision checks and the slide response
    UpdateWorld

    RenderWorld

    Text 0,0,"Arrow keys: drive the ball into the walls and crate   Esc: exit"
    ; CollisionTime is the fraction of the ball's movement step completed
    ; before it hit: 0 = collided immediately, 1 = right at the end of the move
    If CountCollisions(player)>0
        Text 0,20,"CollisionTime(player,1) = "+CollisionTime(player,1)
        Text 0,40,"Hold a key against a wall: the ball is already touching, so the value is tiny"
    Else
        Text 0,20,"CollisionTime: no collisions this frame - push against something"
    EndIf

    Flip

Wend

End

Index