Game / Frame Timing

[kevin]

  Game / Frame timing

  This example  implements a custom timer into the sync refresh.. Unlike the system timer which counts  regardless of your games state, this timer ignores large intervals between calls.  Allowing the game loop to be paused/suspended and resumed without the potential synchronization issues.

PlayBASIC Code: [Select]

   SetFps 30

   Type tSystem
         CurrentTime
         LastMillisecond
         Millisecond
         Frames
   EndType

   Dim System as tSystem


   SyncMe()            

   Do
         Cls          

         print digits$(System.CurrentTime,8)

         if spacekey()
               print "Paused"
               sync
               wait 1000
         endif

         
         if System.CurrentTime>FireTime
                  FireTIme=System.CurrentTime+500         
                  print "Fire"         
         endif
         print FireTime
   
         SyncMe()            
   loop




Psub SyncMe()

      Sync

      ; store the time at last redraw
      System.LastMillisecond=System.Millisecond

      ; current millisecond
      System.Millisecond=Timer()

      Delta=(System.Millisecond-System.LastMillisecond)

      if Delta <50
         System.CurrentTime+=Delta
         System.Frames++
      endif

EndPsub

Usage Example

   This example creates a mock up scene with some moving circles,  the motion of each object is based upon the time past (timer based movement).   You can Pause (Space) and even scale the time passing (Arrows) in the example.   When paused the update routine simply ingores updating the current time, since the current time isn't changing the objects stop moving.  The same applies when you scale time.   If you scale the time pasted by half, then everything in scene moves 50% also.  You can even run time backwards...

PlayBASIC Code: [Select]

   SetFps 61.7

   Type tGameObject
            StartX
            StartY
            EndX
            EndY
            Radius
            Colour   
            StartTime
            EndTime
   EndType

   Dim Object as tGameObject list
   

   Type tSystem
         CurrentTime
         LastMillisecond
         Millisecond
         Frames
         PauseTime
         TimeScaler#
   EndType

   Dim System as tSystem


   System.TimeScaler#=1

; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
; -[MAIN LOOP]--------------------------------------------------------------------
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------


   SyncMe()            

   Do
         Cls          

         print digits$(System.CurrentTime,8)

         if spacekey()
               System.PauseTime=true
         else
               System.PauseTime=false
         endif

         
         DrawObjects()
         
         
         ; trigger some new obejcts at radmon intervals
         if System.CurrentTime>FireTime
                  FireTIme=System.CurrentTime+rndrange(50,500)         
                  for lp =0 to rnd(10)       
                     AddNewObject()
                  next
         endif
         

         ; Scaler the time delta         
         if LeftKey()
             System.TimeScaler#-=0.10
               flushkeys
                  
         endif
         
         if RightKey()
             System.TimeScaler#+=0.10
               flushkeys
         endif
   
         
         print "Time Scaler:"+Str$(System.TimeScaler#)
         SyncMe()            
   loop



; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
; -[SYNC ME]--------------------------------------------------------------------
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------

Psub SyncMe()

      Sync


      if System.PauseTime=false

         ; store the time at last redraw
         System.LastMillisecond=System.Millisecond

         ; current millisecond
         System.Millisecond=Timer()

         Delta=(System.Millisecond-System.LastMillisecond)

         if Delta <50
            System.CurrentTime+=(Delta*System.TimeScaler#)
            System.Frames++
         endif
      endif
      

EndPsub

; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
; -[Draw Objects]---------------------------------------------------------------
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------


Psub DrawObjects()

      CurrentTime=System.CurrentTime



      For Each Object()
      
            if CurrentTime>Object.EndTime
               Object=Null
               continue
            else
   
               TravelTime=Object.EndTime-Object.StartTime
               TimePast#= CurrentTime-Object.StartTime         
               scaler#=TimePast#/TravelTime

               dx#=Object.EndX-Object.StartX
               dy#=Object.EndY-Object.StartY

               x#=Object.StartX+(dx#*Scaler#)
               y#=Object.StartY+(dy#*Scaler#)

               circlec x#,y#,object.radius,true,object.colour
   
            
            endif
      
      next

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 Related Articles

  * Timer Based Movement in PlayBASIC