3D Asteroids Movement Question

No, you are right - I patched up the rotation bug he mentioned and ran it, and it didn't behave like asteroids, but only because pds is too big. It just looked like the ship was accelerating from zero rather than fighting against its previous motion everytime I rotated and thrusted... scale down pds, though, and it becomes clear that it is behaving as you'd expect. So my bad on that one and sorry if I sounded a bit patronising - shoulda' looked more thoroughly at what his code was doing.

I still think, where speed-capping is concerned, it makes more sense to stop thinking in terms of pds as a speed constant and replace it with a variable amount of thrust. As things stand he's going to have to cap pdx and pdy separately, so the ship is going to have a higher top speed diagonally (with max pdx and max pdy combined) than vertically (with max pdx alone) and horizontally (with max pdy alone). I still think a lot of the "action" is occuring on the wrong side of those Sin and Cos equations!

Anyway, my tweaks (no capping) are posted below - the new pds value shows things off a bit better and the pivot work might give Grant a few ideas, what with 'im being new to this 3D malarkey. Ooh also - don't Print, it shifts the display (debug with Text then either use a bitmap or sprite-based font system for release).

;***INITIALIZATION***;
Graphics3D 800,600,16,2
SetBuffer BackBuffer()
SeedRnd MilliSecs()

;***VARIABLES***;
Global pdx#, pdy# ;Player's direction in the 2 1/2D world
Global px#, py# ;Player's coordinates
Const pds# = 0.001 ; Player's speed

;***ENTITIES***;
;Camera 
Global cam = CreateCamera()
CameraRange cam,1,1000
PositionEntity cam,0,10,0
RotateEntity cam,90,0,0

;Spaceship
Global ship = CreatePivot()
shipmesh=CreateCone(8,True,ship);LoadMesh("fighter.3ds")
ScaleEntity ship,.1,.1,.1
PositionEntity ship,0,0,0
RotateEntity shipmesh,90,0,0

;Main Light
light = CreateLight(1)
RotateEntity light,90,0,0

;Skybox
skybox = CreateSphere()
FlipMesh skybox
skytex = CreateTexture(32,32);LoadTexture("stars.jpg")
ScaleTexture skytex,.09,.09
EntityTexture skybox,skytex
ScaleEntity skybox,500,500,500
PositionEntity skybox,0,50,0
EntityOrder skybox,1

;***ARRAYS***;
Dim astmesh(3)
;Big Asteroid
astmesh(1) = CreateSphere(8);LoadMesh("asteroid.3ds")
ScaleMesh astmesh(1),.1,.1,.1
RotateMesh astmesh(1),0,0,0
HideEntity astmesh(1)

;Medium Asteroid
astmesh(2) = CopyMesh(astmesh(1))
ScaleMesh astmesh(2),.5,.5,.5
HideEntity astmesh(2)

;Little Asteroid
astmesh(3) = CopyMesh(astmesh(2))
ScaleMesh astmesh(3),.5,.5,.5
HideEntity astmesh(3)

;***TYPES***;
Type asteroid
Field x#,y# ;Asteroid's position in the 2 1/2D world
Field mesh ;Asteroid's mesh
Field vx#,vy# ;Asteroid's x and y velocities
End Type 

;Game Initialization Functions
CreateAsteroids()

;MAIN LOOP
While Not KeyHit(1)
TestInput()
UpdateShip()
UpdateAsteroids()
UpdateWorld
RenderWorld
;Print pdx#
;Print pdy#
Flip
Wend
End

;***FUNCTIONS***
Function TestInput()
If KeyDown(203)
TurnEntity ship,0,2,0
Else If KeyDown(205)
TurnEntity ship,0,-2,0
End If 
If KeyDown(200)
AsteroidPhysics()
End If 
End Function 

Function CreateAsteroids()
For i = 1 To 3
a.asteroid = New asteroid 
a\x# = 0
a\y# = 0
a\mesh = CopyMesh(astmesh(1))
a\vx# = Rnd(-.1,.1)
a\vy# = Rnd(-.1,.1)
Next
End Function 

Function UpdateAsteroids()
For a.asteroid = Each asteroid
a\x# = a\x# + a\vx#
a\y# = a\y# + a\vy#
If a\x# > 15
a\x# = -15
Else If a\x# < -15
a\x# = 15
End If 

If a\y# > 15
a\y# = -15
Else If a\y# < -15
a\y# = 15
End If
 

PositionEntity a\mesh,a\x,0,a\y#
Next
End Function 

Function AsteroidPhysics()
pdx# = pdx# + Sin(-EntityYaw#(ship))*pds#
pdy# = pdy# + Cos(EntityYaw#(ship))*pds#
End Function 

Function UpdateShip()

px# = px# + pdx#
py# = py# + pdy#
PositionEntity ship,px#,0,py#
End Function