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    box 2d world:step(..) fixed time steps

    GregBUGGregBUG Guru
    edited January 2012 in Game & application design
    hello!
    hi guys! in my game i'm using a fixed time step for physics (according with the box2d manual) with a value of 1/60 sec.
    the problem is that if i test the game an a slow device the physics is a bit slow...

    reading on the net there are some solution with some mixed fixed/variable time steps i tested some but with bad results...
    someone had any hint/code/example for solving this problem? :)

    box2d manual says that the best value is normally 1/60 and using a variable time step is not a good idea... :(
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    Comments

    • atilimatilim Maintainer
      One solution can be using smoothed time steps. The example Hardware/Accelerometer uses low pass filtering to smooth the noisy accelerometer input. If you apply low pass filtering to event.deltaTime, you can achieve nearly constant time steps.

      Also there is a great explanation here: http://bitsquid.blogspot.com/2010/10/time-step-smoothing.html

      Likes: MikeHart, GregBUG

      http://en.wikipedia.org/wiki/Cytorus
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    • GregBUGGregBUG Guru
      edited January 2012
      ok.
      just tested and work fine... (by applying a filter on deltatime) :D

      but i need to redefine all the forces applied to the objects. (according with filtered deltatime)

      when a i go home (now i'm at work) i'll test in more detail.

      thank atilim for the tips.

      I will keep you informed. >:)
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    • atilimatilim Maintainer
      edited January 2012
      great! :)
      http://en.wikipedia.org/wiki/Cytorus
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    • GregBUGGregBUG Guru
      edited January 2012
      just for info....


      works great!

      using filtering on deltatime with a filter value of 0.4 and filtering all the forces applied to the objects.
      		fdt = event.deltaTime * lowfilter + fdt * (1 - lowfilter)
		world:step(fdt, 6, 3)
      and on eli object
      	--if player touch the screen powerup (only if not collision with birds) ..
	if (inTouch) and (eliBirdCollision == false) then
		self.eli_body:applyLinearImpulse(0, -52*fdt , self.eli_px+14, self.eli_py)
		eliSpeed = 2
	else
		-- else powerdown eli...
		self.eli_body:applyLinearImpulse(0, -38*fdt , self.eli_px+14, self.eli_py)
		eliSpeed = 1
	end
      i just needed to increase
      velocity from 2 to 6 in "world:step(fdt, 6, 3)" because on low frame became instable...

      thanks!!!

      Likes: atilim, gorkem

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