Timer Based Movement Star Field

[kevin]

  Timer Based Movement Star Field

    This example creates a simple star field with one subtle difference, the stars movement is plotted in pixels per second, against time in other words .  So the effect isn't attached from the frame rate (for the most part).

    Each star is given a starting position / start time and a speed in pixels per second (1000 milliseconds). The render routine works out how far the star has moved since it's start time (creation time), then plots it in at this current position. If the star has left the screen, it's given a new starting coordinate and it's start time is reset.  So the star is reborn making the effect infinite.  

PlayBASIC Code: [Select]

   Type tStars
         ; XY coordinate of this star
         X#,Y#         
         ; Speed in pixels per second
         Speed#
         ; Time this star was created in milliseconds
         STartTime   
   EndType


   StartTime=Timer()

   Dim Star as tStars list

   For lp=0 to 2000
      Star=New tStars
      Star.x#=rnd(GetSurfaceWidth())
      Star.y#=rnd(GetSurfaceHeight())
      // Speed in pixels per second
      Star.SPeed#=rndrange(100,500)/1000.0   
      Star.StartTime=StartTime
   next




   Do
      cls 


         CurrentTime=Timer()
         lockbuffer
         For each Star()
            TimePast=CurrentTime-Star.StartTime
               x#=STar.x#+(TimePast*Star.Speed)

               dot x#,star.y#            

               ; Check if the star is off the screen (right hand)
               if X#>800
                  ; if it is, reset it's starting X coordinate                     
                  Star.x#=-10
                  ; Randomize it's Y coordinate
                  Star.y#=rnd(Getsurfaceheight())
                  ; set it's starting time to now.
                  Star.StartTime=CurrentTime
               endif

         next
         lockbuffer
   
      Sync
   loop

 Related Articles

   Timer Based Movement
    Vsync / Frame Rate Scaling
   Timer Based Movement with Vsync Tweening
   Handling Multiple Animations using Timer()
   Consistent Game Timing