There are utilities to use a UGEN outside the definition of a DSP and the next examples show them step by step.

The first example is really trivial and you can replace it with a simple let-over-lambda, but I prefer to focus the attention on the utilities. Under the hood, a UGEN is let-over-lambda plus vitamins (VUGs, nested UGENs, C heap management, automatic inference of init- and performance-time variables, etc).

We start with a new UGEN called INCR-EDULA:

(in-package :scratch)

(define-ugen incr-edula fixnum ((start fixnum) (edge fixnum))
  (with ((n (1- start)))
    (setf n (mod (1+ n) edge))))


SCRATCH> (ugen 'incr-edula)

The result of the function INCR-EDULA is another function, usable to generate UGEN-INSTANCEs.

SCRATCH> (defvar *eugenia* (funcall (incr-edula 0 8)))
SCRATCH> *eugenia*

*EUGENIA* is ready for the performance (all is initialized).

(defun counts (toys)
  (loop repeat toys collect (funcall (ugen-perf-function *eugenia*))))

SCRATCH> (counts 12)
(0 1 2 3 4 5 6 7 0 1 2 3)

Now we can define a setter (not a dog) to change the edge. The default for the name of the setter is SET-[UGEN-NAME]-[CONTROL-NAME]

(define-ugen-control-setter incr-edula edge)

SCRATCH> (set-incr-edula-edge *eugenia* 5)
SCRATCH> (counts 12)
(4 0 1 2 3 4 0 1 2 3 4 0)

The follow line defines a setter called INCR-EDULA-FROM to change the START value:

(define-ugen-control-setter incr-edula start incr-edula-from)

SCRATCH> (incr-edula-from *eugenia* 2)
SCRATCH> (counts 12)
(2 3 4 0 1 2 3 4 0 1 2 3)

Finally, the *EUGENIA*'s reinitialization:

(funcall (ugen-reinit-function *eugenia*) 0 7)

SCRATCH> (counts 16)
(0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1)

The return type of the next UGEN is SAMPLE…

(define-ugen zibaldone sample (night deep (darkness fixnum))
  (buzz night deep darkness))

SCRATCH> (ugen 'zibaldone)
SCRATCH> (defvar *notturno* (funcall (zibaldone 100 .5 30)))
SCRATCH> *notturno*

… but the return type of the performance function is NIL. We retrieve the result from the foreign pointer:

(defun star-samples (n)
  (loop repeat n do (funcall (ugen-perf-function *notturno*))
        collect (smp-ref (ugen-return-pointer *notturno*) 0)))

SCRATCH> (star-samples 3)
(0.5d0 0.486606790129606d0 0.44769321522927535d0)
SCRATCH> (star-samples 3)
(0.3869151587690795d0 0.30990888519118d0 0.22366438072673978d0)

The last argument of DEFINE-UGEN-CONTROL-SETTER is the type of the value passed to the setter. For example:

(define-ugen-control-setter zibaldone night nil real)

where the expansion of the macro is

            (TYPE REAL VALUE))

and you can notice coercing around the input value. Now we can change the night by using a real number instead of a value of type SAMPLE:

SCRATCH> (set-zibaldone-night *notturno* 1798)
SCRATCH> (star-samples 3)
(0.13575758294800522d0 -0.01625060660788103d0 -0.03490033405549335d0)

If the setter is defined without to specify the type of the input value, it's better to add `(declaim (inline set-zibaldone-night))' to avoid consing, because the type of the input value is SAMPLE. Idem when the type is a foreign pointer.

There is also a low level utility to get the pointer to the memory used to store the value of a control and the function of no arguments to update the dependencies (if it exists):

SCRATCH> (ugen-control-pointer *notturno* 'night)
#.(SB-SYS:INT-SAP #X0072F500)
#<CLOSURE (LAMBDA ()) {1005B7253B}>

Note: if the control is not represented by a foreign object, the returned pointer is a function of no arguments to call to get the control value. For example, DARKNESS is of fixnum type, therefore

SCRATCH> (ugen-control-pointer *notturno* 'darkness)

SCRATCH> (funcall *)

So, a low level way to transform the night is

(multiple-value-bind (ptr fn)
    (ugen-control-pointer *notturno* 'night)
  (setf (smp-ref ptr 0) (sample 1821))
  (when fn (funcall fn)))

Le parole notte notturno ec., le descrizioni della notte ec., sono poeticissime, perché la notte confondendo gli oggetti, l'animo non ne concepisce che un'immagine vaga, indistinta, incompleta, sì di essa che quanto ella contiene. Così oscurità, profondo ec. ec. – Giacomo Leopardi (Zibaldone)

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