Vsync / Frame Rate Scaling

[kevin]

 Vsync / Frame Rate Scaling V0.01

  This example shows an approach for dealing with situations where you want to VSYNC the  display, but we have no way of knowing how fast the users videocard/monitor can Vsync.

  So the idea here is that we calc a scaler between the our ideal rate (the rate we imagine our game running at) and the end users actual display rate, which could be anything!   Then we apply this scaler to our movement speeds.  Which will give us the distance our objects have moved  since the _user_ last saw the screen.  So we're scaling our ideal rate to theirs, which should smooth out motion somewhat.    

  Of course this is assuming the user has Vsync enabled in their display drivers, they might not..  


Controls:

      Arrows = Move Camera
      Space = Change sync method
      ESC = EXIT

PlayBASIC Code: [Select]

  // open a Full Screen exclusive screen mode
    OpenScreen 1024,768,32,2


 // make a black/white pattern image as backdrop
      Dim Cols(1)
      Cols(0)=$304050
      Cols(1)=$80a080
      
      Size =32
      width=Size*8
      height=Size*8
      for ylp=0 to Height/Size 
         for xlp=0 to Width/Size
            x1=xlp*size
            x2=x1+size
            y1=ylp*size
            y2=y1+size
            boxc x1,y1,x2,y2,true,cols( cell&1)
            inc cell
         next
      next
      GetImage 1,0,0,width,height
   

   // ===========================================================
   // Init the Mode the demo will start in.
   // ===========================================================

   //     mode =0 Vsync display mode
   //     mode =1 SetFps base refresh.
   
      Mode=0   
      ScreenVsync True


   
   // This is the FPS rate our game should be running at.   
      Game_Required_VSYNC#=80

   // try an calc the vysnc rate of the users computer.. 
      Monitor_Vsync_Rate#=   Calc_Monitor_Sync_rate()
   
   // calc the scaler between our ideal rate and the computers Vsync rate.
     Game_Movement_Scaler#=Game_Required_VSYNC#/Monitor_Vsync_Rate#


   // Make a camera
      cam=NewCamera()


   // ===========================================================
   // Start of Test loop   
   // ===========================================================
   Do

      if mode=0
         Mode$="Monitor Vysnc"
      else
         Mode$="SetFps" 
      endif


      // Speed of object in pixels per frame and games ideal rate

      MovementSpeed#=10

      if Mode=0
         // in Vsync mode wea pply the VSYNC scaler to our movement speed
         Speed#=   MovementSpeed#* Game_Movement_Scaler#
      endif

      if Mode=1
         // in Setfpos mode we just use the movement value as is
         Speed#=   MovementSpeed#* Game_Movement_Scaler#
      endif


      // ===========================================================
      // Convert this speed 
      // ===========================================================

      if LeftKey()
            movecamera Cam,-Speed#,0
      endif

      if RightKey()
            movecamera Cam,Speed#,0
      endif

      if upKey()
            movecamera Cam,0,-Speed#
      endif

      if downKey()
            movecamera Cam,0,Speed#
      endif


      // ===========================================================
      // draw the scene   so we've something to look at
      // ===========================================================
         CaptureToScene
         ClsScene

         for ylp=0 to 20
            for xlp=0 to 100
               Xpos=GetImageWidth(1)*Xlp   
               Ypos=GetImageHeight(1)*ylp   
               DrawIMage 1,Xpos,Ypos,true
            next
         next      
                  
         drawcamera Cam


      // ===========================================================
      // Draw the info about this scene
      // ===========================================================
   
      ink $ff00ff
      text 0, 0,"             Fps Rate:"+str$(Fps())
      text 0,20,"    Monitor Sync Rate:"+str$(Monitor_Vsync_Rate#)
      text 0,40,"Games Ideal Sync Rate:"+str$(Game_Required_VSYNC#)
      text 0,60,"               Scaler:"+str$( Game_Movement_Scaler#)
      text 0,80,"                 Mode:"+Mode$


      // ===========================================================
      // Check if the space key was press
      // ===========================================================
      if spacekey()

            // flush the mode
            Mode=1-mode

            // if mode =0 then we'll set PB to VSYNC the display
            if Mode=0
                screenvsync true
               setfps 0
            else
               // mode <>0 then we use SetFps to limit the rate
                screenvsync false
               setfps Game_Required_VSYNC#
            endif   

            // Flush keys
            Flushkeys


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Related To

  Timer Based Movement  (Tutorial)
  Timer Based Movement with Vsync Tweening