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

GregBUG

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...

atilim

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

GregBUG

ok.
just tested and work fine... (by applying a filter on deltatime)

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.

atilim

great!

GregBUG

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!!!