Hello,
When using GLUT, if you want your display function to be called as
fast as possible by the GLUT main loop, you do this:
(glutIdleFunc glutPostRedisplay)
But what if you want to call the display-function 'n' times per
second?
I currently have a procedure 'frames-per-second' in this library:
http://github.com/dharmatech/agave/blob/master/glamour/frames-per-second.sls
You use it like so:
(glutIdleFunc (frames-per-second 30))
In that case, 'glutPostRedisplay' will be called at most 30 times per
second.
The thing is, looking at the 'frames-per-second' library, there surely
is an abstraction there.
One approach to the factor is as follows:
----------------------------------------------------------------------
(import (srfi :19 time))
(define (current-time-in-nanoseconds)
(let ((val (current-time)))
(+ (* (time-second val) 1000000000)
(time-nanosecond val))))
(define-syntax limit-call-rate
(syntax-rules ()
((limit-call-rate calls-per-second (proc param ...))
(let ((last-call-time 0)
(nanoseconds-per-call (/ 1e9 calls-per-second)))
(define (nanoseconds-since-last-call)
(- (current-time-in-nanoseconds)
last-call-time))
(lambda (param ...)
(if (> (nanoseconds-since-last-call) nanoseconds-per-call)
(begin
(set! last-call-time (current-time-in-nanoseconds))
(proc param ...))))))))
----------------------------------------------------------------------
Let's define a procedure that displays it's three arguments:
(define (display-three a b c)
(display a)
(display b)
(display c)
(newline))
Make a version of it which will run at most once per second:
(define display-three/limited
(limit-call-rate 1 (display-three a b c)))
Test it out:
(let loop ()
(display-three/limited (random 10) (random 10) (random 10))
(loop))
...
Another example: have GLUT call the display function at most 30 times
per second:
(glutIdleFunc (limit-call-rate 30 glutPostRedisplay))
Anywho, just wanted to check to see if anyone has something like this
already or suggestions of other approaches.
Ed
PS: I've been wondering if we need an 'r6rs-cafe' list for the general
R6RS community? I'd post design questions such as these there for
example. The r6rs-cafe would have a much narrower scope than
comp.lang.scheme; c.l.s also suffers from cross posting and spam. The
existing r6rs-discuss seems to be for flames. :-)
