Timing movements in seconds?

Blitz3D Forums/Blitz3D Beginners Area/Timing movements in seconds?

Rogue Vector

(Posted 2005) [#1]

Hi,

I need a timing system that uses seconds and not animation frames to govern the movements of objects in a scene.

The CreateTimer(), WaitTimer() approach is no good in this instance because it uses frame frequency.

Can someone who knows basic mathematics show me why the following code doesn't work.

; Basic timed movement
; ------------------
;
; doesn't work. Why?
;
; need to move the object over a set distance (6.5) in a set time (3 secs) 
; time needs to be in seconds NOT frames


; Set 3D graphics mode
Graphics3D 640,480,16,0
SetBuffer BackBuffer()

camera=CreateCamera()
light=CreateLight()

cone=CreateCone( 32 )
PositionEntity cone,-3,0,5

distance#   = 6.5 ;blitz units
time#       = 3.0 ;secs
speed#      = Float(distance / time)

currentpos# = 0.0 

While Not KeyDown( 1 )
		
	If (currentpos < distance)
	
		MoveEntity(cone, speed, 0, 0)
		currentpos = currentpos + speed
		
	EndIf

	UpdateWorld()
	RenderWorld()
	
	Flip

Wend

ClearWorld()

End

Thanks,

Rogue Vector

SoggyP

(Posted 2005) [#2]

Greetings Puppies,

Check out the Millisecs() command and base your stuff on that?

Peace,

Jes

Rogue Vector

(Posted 2005) [#3]

I know about the millisecs() command.

But there are still problems with the timing.

Objects move in a jerky way and inaccuracy creeps in.

Observe,

; Basic timed movement
; ------------------
; 
; need to move the object over a set distance (6.5) in a set time (3 secs) 
; time needs to be in seconds NOT frames
;
; PROBLEM - NOT ACCURATE and the object needs to move more smoothly and eliminated the jerkyness 
;-----------------------------------------------------------------------------

; Set 3D graphics mode
Graphics3D 640,480,16,0
SetBuffer BackBuffer()

camera=CreateCamera()
light=CreateLight()

cone=CreateCone( 32 )
PositionEntity cone,-3,0,5

distance#   = 6.5 ;blitz units
time#       = 3.0 ;seconds
speed#      = Float(distance / time);result is blitz units per second

currentpos# = 0.0 

clock = 0
timer = 0

While Not KeyDown( 1 )

	clock = MilliSecs()

	If (timer + Float(1000 / 4)  < clock) ;clock every 250 milliseconds (1/4 second)
		
		If (currentpos < distance)
		
			MoveEntity(cone, speed / 4 , 0, 0)
			currentpos = currentpos + speed / 4
				
		EndIf

		timer = clock
		
	EndIf	

	UpdateWorld()
	RenderWorld()
		
	Text 2, 5, CurrentTime$()
	
	Flip
	
Wend

ClearWorld()

End

Rogue Vector

HappyCat

(Posted 2005) [#4]

Instead of moving the object every 250 milliseconds, you need to move the object based on the number of miilisecs since the last update. Like this:

; Set 3D graphics mode
Graphics3D 640,480,16,0
SetBuffer BackBuffer()

camera=CreateCamera()
light=CreateLight()

cone=CreateCone( 32 )
PositionEntity cone,-3,0,5

distance#     = 6.5 ;blitz units
time#         = 3.0 ;seconds
speed#        = Float(distance / time);result is blitz units per second
speedpertick# = Float(speed#/1000);result is blitz units per tick

currentpos# = 0.0 

clock = MilliSecs()
starttime = clock


While Not KeyDown( 1 )
	
	ticks = MilliSecs() - clock
	clock = MilliSecs()

	If (currentpos < distance)
		distancemovedthisupdate# = speedpertick# * ticks
		MoveEntity(cone, distancemovedthisupdate, 0, 0)
		currentpos = currentpos + distancemovedthisupdate
	Else
		Text 2, 60, "Took " + (MilliSecs() - StartTime) + " milliseconds"
		Flip
		WaitKey
		End
	End If
		
	UpdateWorld()
	RenderWorld()
		
	Text 2, 5, CurrentTime$()
	Text 2, 30, currentpos

	Flip
	
Wend

ClearWorld()

End

That way it always moves at the same speed regardless of the framerate.

Edit: sorry, I didn't notice the significance of currentpos at first :-)

Edit: also, it'll never be *exactly* 6.5 units, or 3000 milliseconds because of the vagaries of PC performance, (my PC was doing a frame about every 17 milliseconds, which just doesn't divide cleanly into 3000) but it should be accurate enough for most purposes.

Rogue Vector

(Posted 2005) [#5]

Thanks!

Rogue Vector,

HappyCat

(Posted 2005) [#6]

No problem.

WolRon

(Posted 2005) [#7]

Rogue Vector, take a look at my Frame Limiting Code (the link is on the left) to see how to apply it to your games.
http://home.cmit.net/rwolbeck/programmingtutorial