apfelmus at quantentunnel.de
Mon Oct 1 10:49:12 CEST 2012
Miguel Negrao wrote:
> Thanks for the explanation. I was wondering, how would one translate
> this Yampa code into reactive-banana:
> fallingBall :: Pos -> Vel -> SF () (Pos, Vel)
> fallingBall y0 v0 = proc () -> do
> v <- (v0 +) ˆ<< integral -< -9.81
> y <- (y0 +) ˆ<< integral -< v
> returnA -< (y, v)
> fallingBall’ :: Pos -> Vel -> SF () ((Pos,Vel), Event (Pos,Vel))
> fallingBall’ y0 v0 = proc () -> do
> yv@(y, _) <- fallingBall y0 v0 -< ()
> hit <- edge -< y <= 0
> returnA -< (yv, hit ‘tag‘ yv)
> bouncingBall :: Pos -> SF () (Pos, Vel)
> bouncingBall y0 = bbAux y0 0.0
> bbAux y0 v0 = switch (fallingBall’ y0 v0) $ \(y,v) -> bbAux y (-v)
> Would it be possible to do this without dynamic event switching ?
> What about with the new event switching in v0.7 ? Also, is it possible (and
> is it easy ?) to do looping such as it is done in Yampa using the the
> loop arrow in reactive-banana/classic FRP ?
The Animation.hs example may help
Essentially, the main difference is that reactive-banana doesn't have
functions like integral or edge because they depend on an implicit
time step. In reactive-banana, you have to manage time yourself, for
instance by making a timer event from a wxTimer.
To calculate velocity and position, you can you use accumE on the
timer event. To do collision detection, you can check whether the ball
will move below the floor at each time step. Dynamic event switching is
not needed here.
For a more complex example, have a look at Andreas Bernstein's paddle
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