Like this?
physics t (b, w1, w2, w1x, w2x) = if w1x < w2x then
({ b | y = b.y + t*b.vy , x = b.x + t*b.vx },
w1 |> move (5,0),
w2 |> move (-5,0),
w1x + 5,
w2x - 5
)
else if (bird.x < w1x || bird.x > w2x )then
(b, w1, w2)
else
(b, w1, w2, w1x, w2x)
在 2016年6月21日星期二 UTC+8下午12:09:03，Nick H写道：
>
> You will need to add another if-else condition to your physics function,
> where you compare b.x with w1x and w2x.
>
> On Mon, Jun 20, 2016 at 8:47 PM, <cass...@gmail.com <javascript:>> wrote:
>
>> Below is my whole code. The wall is moving. I wonder know how to
>> determine whether the bird touch the two walls. The bird will die if it
>> touch the walls when the walls stop moving.
>>
>>
>>
>>
>> import Color exposing (..)
>> import Graphics.Collage exposing (..)
>> import Graphics.Element exposing (..)
>> import Keyboard
>> import Text
>> import Time exposing (..)
>> import Window
>>
>> -- SIGNALS
>>
>> bird = { x=0, y=0, vx=0, vy=0 }
>>
>> -- moves the walls only
>> physics t (b, w1, w2, w1x, w2x) = if w1x < w2x then
>> ({ b | y = b.y + t*b.vy , x = b.x + t*b.vx },
>> w1 |> move (5,0),
>> w2 |> move (-5,0),
>> w1x + 5,
>> w2x - 5
>> )
>> else
>> (b, w1, w2, w1x, w2x)
>>
>> -- moves the bird only
>> walk {x,y} (b, w1, w2, w1x, w2x) = ({ b | vx = toFloat x, vy = toFloat y
>> }, w1, w2, w1x, w2x)
>>
>> step (dt, keys) =
>> walk keys >> physics dt
>>
>> (gameWidth,gameHeight) = (500,500)
>>
>>
>> wall1 = toForm (collage gameWidth gameHeight
>> [ rect 100 100 |> filled (rgb 250 230 0) |> move (50-gameWidth/2,
>> gameHeight/2-50)
>> ,rect 80 100 |> filled (rgb 250 230 0) |> move (40-gameWidth/2,
>> gameHeight/2-150)
>> , rect 50 100 |> filled (rgb 250 230 0) |> move (25-gameWidth/2,
>> gameHeight/2-250)
>> , rect 100 100 |> filled (rgb 250 230 0) |> move (50-gameWidth/2,
>> gameHeight/2-350)
>> , rect 80 100 |> filled (rgb 250 230 0) |> move (40-gameWidth/2,
>> gameHeight/2-450)
>>
>> ])
>>
>> wall2 = toForm (collage gameWidth gameHeight
>> [ rect 100 100 |> filled (rgb 250 230 0) |> move (gameWidth/2-50,
>> gameHeight/2-50)
>> , rect 120 100 |> filled (rgb 250 230 0) |> move (gameWidth/2-60,
>> gameHeight/2-150)
>> , rect 50 100 |> filled (rgb 250 230 0) |> move (gameWidth/2-25,
>> gameHeight/2-250)
>> , rect 100 100 |> filled (rgb 250 230 0) |> move (gameWidth/2-50,
>> gameHeight/2-350)
>> , rect 120 100 |> filled (rgb 250 230 0) |> move (gameWidth/2-60,
>> gameHeight/2-450)])
>>
>>
>> render (w',h') (bird, wall1, wall2, w1x, w2x) =
>> let (w,h) = (toFloat w', toFloat h')
>> src = "bee.PNG"
>> in collage w' h'
>>
>> [ rect gameWidth gameHeight |> filled (rgb 174 238 238)
>> , toForm (image 50 50 src) |> move (bird.x, bird.y)
>> , wall1
>> , wall2
>> -- text (Text.fromString (toString (w1x, w2x)))
>> ]
>>
>>
>> -- bird
>> input = let delta = Signal.map (\t -> t/10) (fps 10)
>> in Signal.sampleOn delta (Signal.map2 (,) delta Keyboard.arrows)
>>
>> main = Signal.map2 render Window.dimensions (Signal.foldp step (bird,
>> wall1, wall2, -gameWidth/2 + 100, gameWidth/2 - 100) input)
>>
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