pv_RandWipe bufferA bufferB wipe trig

Cross fades between two sounds by copying bins in a random order.

bufferA = fft buffer A.  bufferB = fft buffer B.  wipe = copies
bins from bufferB in a random order (0, 1).  trig = select new
random ordering.

> withSC3 (\fd -> do { async fd (b_alloc 10 2048 1)
>                    ; async fd (b_alloc 11 2048 1) })

> let { n0 = randomRs (400.0, 1000.0) (mkStdGen 0)
>     ; n1 = randomRs (80.0, 400.0) (mkStdGen 1)
>     ; n2 = randomRs (0.0, 8.0) (mkStdGen 2)
>     ; o0 = map (\n -> lfSaw AR n 0 * 0.1) (take 6 n0)
>     ; o1 = map (\n -> lfPulse AR n 0.0 0.2) (take 6 n1)
>     ; o2 = map (\n -> sinOsc KR n 0 * 0.2) (take 6 n2)
>     ; a = mix (mce o0)
>     ; b = mix (mce (zipWith (\p s -> p * (max s 0.0)) o1 o2))
>     ; f = fft' 10 a
>     ; g = fft' 11 b
>     ; x = mouseX KR 0 1 Linear 0.1
>     ; y = mouseY KR 0 1 Linear 0.1 }
> in do { h <- pv_RandWipe f g x (y >* 0.5)
>       ; audition (out 0 (pan2 (ifft' h) 0 0.5)) }