Foreign-Call Controller
Description
Allows any Lisp (or Scheme) program to be used as a controller. To take advantage of this function, you should have some knowledge of the Lisp (or Scheme) programming language. The fact that it can replicate Scheme programs is for backwards-compatibility, since old versions of Modalys used a Scheme interface instead of a Lisp interface.
(make-controller 'foreign-call ... )
Syntax and Default Values
The 'foreign-call controller can be created using the following Lisp syntax:
(make-controller 'foreign-call dimension period foreign_function (list controller1 controller2 ... ))
Parameters
The 'foreign-call controller takes the following arguments:
- dimension: number of dimensions for the output controller.
- period: the time between controller updates (in synthesis seconds).
- foreign_function: a Lisp or Scheme function representing the expression to be evaluated. see details, below.
- controller1, controller2, etc...: controllers to "plug-in" to the math expression.
The output controller can be optionally re-sampled using the period argument. A period of 0, as always, indicates the controller will be updated every sample.
The Lisp or Scheme lambda function with no arguments, says how to update the "output latch" from the "input latches". See description, below, for details.
A variable number of controllers may be provided as a list.
Discussion
Here is a practical example of how to use the 'foreign-call controller to multiply two controllers (my-ctl1 and my-ctl2):
(make-controller 'foreign-call 1 0
(foreign-callable (lambda (input output)
(vset output 0 (* (vget input 0 0) (vget input 1 0))) ))
(list my-ctl1 my-ctl2))
(make-controller 'expression 1 0 "in(1,1)*in(2,1)" my-ctl1 my-ctl2)
(make-controller 'arithmetic 1 "*" my-ctl1 my-ctl2)
(make-controller 'foreign-call 1 0
(foreign-callable (lambda (ins outs)
(vset outs 0 (get-info 'speed access-ref)) ))
'())
Although we generally recommend using the 'expression, 'arithmetic or other controllers when and where possible (did we mention that they were a lot faster???!), there may be some advanced or expert techniques which require the 'foreign-call controller to do specific tasks, so the function has been retained in the Modalys environment.
Options
Lambda Function Syntax
It's worth studying the update function a bit (actually you need to know how to program a little bit in Lisp, Scheme or a related programming language in order to really understand this well). The update function must begin like this (of course, "inputs" and "output" could be other variable names like "ins" and "out"):
(foreign-callable (lambda (inputs output) . . . ))
(vset output 0 31.2)
(vset output 1 31.2)
(vget inputs 0 0)
(vget inputs 0 1)
(vget inputs 1 0)
(vget inputs 18 21)
(foreign-callable (lambda (inputs output) (vset output 0 (* (vget inputs 0 0) (vget inputs 1 0)))))
This is a useful general-programming-like way of using a controller, however for most basic math operations you can use the 'arithmetic controller or for more complex expressions, the 'expression controller.
Retro-Compatibility
This controller was formerly called (make-controller 'scheme ... ) and had a slightly different syntax where the number of input controllers had to be explicitly given before the list containing them:
(make-controller 'scheme dimension period foreign_function num_input_ctlrs (list controller1 controller2 ... ))
(make-controller 'scheme 1 0
(lambda ()
(vset 0 (* (vget 0 0) (vget 1 0))) )
2 (list my-ctl1 my-ctl2))