On Wed, Jul 10, 2013 at 2:15 PM, Just
Hello,
I'm trying to get a grasp of netwire by implementing a bouncing ball simulation and I'm failing. The ball starts from the ground with a given velocity and when hitting the ground the wire inhibits successfully. Now I'm kinda stuck.
I've never used netwire (although I've used yampa and recative-banana), so I can't give you help with the code, but maybe I can help with the concepts. I think I see what is wrong. You need to keep applying forces to the ball. Right now, the code says, once the ball falls below a certain point, stop applying the force (eg., clamp the output of the integral). Instead, you could apply an upward force at the point of impact. You can get this from newton's third law (equal and opposite reaction). The easiest way to see a bounce would be to simply negate the velocity when you detect a collision with the ground. A more accurate way might involve some calculations to figure out the impulse, but then you'll need more things like the mass of the ball. I hope that helps, Jason
How can I make the ball bounce?
Here is the code:
{-# LANGUAGE Arrows #-}
module Main where
import Control.Wire import Prelude hiding ((.), id) import Control.Concurrent
type Pos = Double type Vel = Double type ObjState = (Pos, Vel)
testApp :: Pos -> Vel -> WireP () ObjState testApp p0 v0 = proc _ -> do v <- integral_ v0 -< -9.81 p <- integral1_ p0 -< v when (>= 0) -< p returnA -< (p, v)
main :: IO () main = loop' (testApp 0 30) clockSession where loop' w' session' = do threadDelay 1000000 (mx, w, session) <- stepSessionP w' session' () case mx of Left ex -> putStrLn ("Inhibited: " ++ show ex) Right x -> putStrLn ("Produced: " ++ show x) loop' w session
Thanks in advance!
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