Netwire bouncing ball
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. 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!
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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Just
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.
How can I make the ball bounce?
A very simple way to do this is to use integralLim_ instead of integral_. It allows the ball itself to handle the bouncing. A less invasive way (i.e. you can add it to your example) is to use the (-->) combinator: ball = integral_ 0 . integral_ 40 . (-9.8) aboveGround = require (>= 0) bouncingBall = aboveGround . ball --> bouncingBall While this gives you a bouncing ball, the ball will not follow real physics. Once the ball hits the ground, it will just start over with its original velocity. integralLim_ is the correct solution. Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.
On 07/10/2013 11:44 PM, Ertugrul Söylemez wrote:
A very simple way to do this is to use integralLim_ instead of integral_. It allows the ball itself to handle the bouncing. A less invasive way (i.e. you can add it to your example) is to use the (-->) combinator:
ball = integral_ 0 . integral_ 40 . (-9.8)
aboveGround = require (>= 0)
bouncingBall = aboveGround . ball --> bouncingBall
While this gives you a bouncing ball, the ball will not follow real physics. Once the ball hits the ground, it will just start over with its original velocity. integralLim_ is the correct solution.
Thank you very much, this works as expected and is easy to understand. However a complete example of a bouncing ball would be super awesome since I have trouble to get it work with integralLim_. My first try was to use object_ from Control.Wire.Prefab.Move but got stuck very quickly. I think this would be a good addition to the quickstart tutorial.
On 07/11/2013 05:52 PM, Just wrote:
On 07/10/2013 11:44 PM, Ertugrul Söylemez wrote:
A very simple way to do this is to use integralLim_ instead of integral_. It allows the ball itself to handle the bouncing. A less invasive way (i.e. you can add it to your example) is to use the (-->) combinator:
ball = integral_ 0 . integral_ 40 . (-9.8)
aboveGround = require (>= 0)
bouncingBall = aboveGround . ball --> bouncingBall
While this gives you a bouncing ball, the ball will not follow real physics. Once the ball hits the ground, it will just start over with its original velocity. integralLim_ is the correct solution.
Thank you very much, this works as expected and is easy to understand. However a complete example of a bouncing ball would be super awesome since I have trouble to get it work with integralLim_.
My first try was to use object_ from Control.Wire.Prefab.Move but got stuck very quickly.
I think this would be a good addition to the quickstart tutorial.
It would indeed be a fantastic addition - this is almost exactly what I was trying to do as my example netwire project. For a bit more support, I was trying to move a point from x=0 to x=10, and then back to x=0 - and so on. I got as far as getting to x=10, but then had no idea how to reverse the direction and make the whole thing cycle. I was told to read about ArrowLoop, but sadly I never got much further. - ollie
Just
Thank you very much, this works as expected and is easy to understand. However a complete example of a bouncing ball would be super awesome since I have trouble to get it work with integralLim_.
My first try was to use object_ from Control.Wire.Prefab.Move but got stuck very quickly.
object_ is a generalization of integralLim_. It pretty much allows you to encode any moving behavior you want. In general I recommend going with the integral* wires as far as possible.
I think this would be a good addition to the quickstart tutorial.
Thanks for your feedback. I should write a complete example application in the next revision. Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.
participants (4)
-
Ertugrul Söylemez -
Jason Dagit -
Just -
Oliver Charles