Here's the working routine:
; Sphere-Box Intersection Routine
; Blitz version by simon@..., based on code found at http://www.acm.org/tog/GraphicsGems/gems/BoxSphere.c
; See also http://www.realtimerendering.com/int/ and http://www.magic-software.com/Intersection.html for some more (non-Blitz flavoured) intersection routines
; This routine is a fast, accurate way of testing to see whether a solid sphere intersects a solid axis-aligned box.
; Useful to act as an activation zone in games - i.e. if sphere is in invisible zone then activate event.
; Use mouse to rotate camera, left and right mouse buttons to move camera forward/backward
; Move sphere by using cursor keys and r/f for rise/fall
; When the sphere touches the box, a 'collision' message should appear in the top-left hand corner of the screen
; Initialise
width=640
height=480
Graphics3D width,height,0,2
SetBuffer BackBuffer()
MoveMouse width/2,height/2
cam=CreateCamera()
PositionEntity cam,0,100,-100
RotateEntity cam,30,0,0
light=CreateLight()
; Set dimensions for box/sphere, then create them using these dimensions
bx#=0 ; box x
by#=0 ; box y
bz#=0 ; box z
bw#=50 ; box width
bh#=50 ; box height
bd#=50 ; box depth
sx#=0 ; sphere x
sy#=0 ; sphere y
sz#=0 ; sphere z
sr#=5 ; sphere radius
box=CreateCube()
EntityColor box,255,255,0
FitMesh box,0,0,0,bw,bd,bh
PositionEntity box,bx,by,bz
sphere=CreateSphere()
EntityColor sphere,255,0,0
ScaleEntity sphere,sr,sr,sr
PositionEntity sphere,sx#,sy#,sz#
While Not KeyDown(1)
; Move camera
mxs=mxs+MouseXSpeed()
mys=mys+MouseYSpeed()
RotateEntity cam,mys,-mxs,0
MoveEntity cam,0,0,MouseDown(1)-MouseDown(2)
; Move sphere
If KeyDown(203) Then sx#=sx#-1
If KeyDown(205) Then sx#=sx#+1
If KeyDown(19) Then sy#=sy#+1
If KeyDown(33) Then sy#=sy#-1
If KeyDown(200) Then sz#=sz#+1
If KeyDown(208) Then sz#=sz#-1
sx#=sx#+mx#
sy#=sy#+my#
sz#=sz#+mz#
PositionEntity sphere,sx#,sy#,sz#
RenderWorld
; Test to see if sphere intersects box
If SphereBoxIntersection(sx#,sy#,sz#,sr#,bx#,by#,bz#,bw#,bh#,bd#)=True Then Text 0,0,"Collision"
Flip
Wend
Function SphereBoxIntersection(sx#,sy#,sz#,sr#,bx#,by#,bz#,bw#,bh#,bd#)
; sx#,sy#,sz# = sphere x,y,z centre co-ordinates
; sr# = sphere radius
; bx#,by#,bz# = box x,y,z corner co-ordinates
; bw#,bh#,bd# = box width,height,depth
Local dmin#=0
Local sr2#=sr*sr
; x axis
If sx < bx
dmin=dmin+((sx-bx)*(sx-bx))
Else If sx>(bx+bw)
dmin=dmin+(((sx-(bx+bw)))*((sx-(bx+bw))))
EndIf
; y axis
If sy < by
dmin=dmin+((sy-by)*(sy-by))
Else If sy>(by+bh)
dmin=dmin+(((sy-(by+bh)))*((sy-(by+bh))))
EndIf
; z axis
If sz < bz
dmin=dmin+((sz-bz)*(sz-bz))
Else If sz>(bz+bd)
dmin=dmin+(((sz-(bz+bd)))*((sz-(bz+bd))))
EndIf
If dmin#<=sr2# Then Return True Else Return False
End Function
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