slowcat.c: How to slow down animation

In article <CG9...@undergrad.math.uwaterloo.ca> Bernard Lam wrote:

>   I'm just wondering how to slow down the animated files.  When I view the
> files using the 'cat' command in UNIX, it goes so fast that I can't see it.

Since this group started I had the same problem. Here is a little filter
I knocked together to solve the problem, and lets you specify the output
rate. I've only tested it on a Sun sparcstation, under SunOS 4.1.3. It's
not pretty, but it works here!

Happy viewing !
		Dave.

-------------------------------- Cut here --------------------------------
/* slowcat.c */
#include <stdio.h>
#include <sys/types.h>
#include <sys/time.h>

/*
 * Cat files, but delay the characters. Useful for ASCII animations
 * when the line (eg xterm) is too fast. The output rate is in units
 * of characters per second, and defaults to 1000.
 *
 * Usage: slowcat [-r rate] [file...]
 */

extern int getopt();			/* Decodes option args. */
extern char *optarg;			/* Required by getopt() */
extern int optind, opterr;		/* Required by getopt() */

long interval;				/* To wait between characters */

#define DEFAULT_RATE	1000		/* Characters per second */
#define M		1000000L	/* us (tv_usec units) per second */

main(int argc, char **argv)
{
    int rate = DEFAULT_RATE;
    register int c;

    while ((c = getopt(argc, argv, "r:")) != -1)
    {
	switch (c)
	{
	case 'r':			/* Rate, chars per second */
	    if ((rate = atoi(optarg)) < 10)
		rate = 10;
	    break;

	case '?':
	default:
	    fputs("Usage: slowcat [-r rate] [file...]\n", stderr);
	    exit(1);
	}
    }

    interval = M / rate;

    if (optind < argc)
    {
	for ( ; optind < argc;  ++optind)
	{
	    FILE *fp;

	    if (fp = fopen(argv[optind], "r"))
	    {
		scat(fp);
		fclose(fp);
	    }
	    else
		perror(argv[optind]);
	}
    }
    else
	scat(stdin);
}

scat(FILE *fp)
{
    long uwait;			/* Wait time in microseconds */
    struct timeval time;	/* long tv_sec, tv_usec; Secs & microsecs */
    struct timeval next_due;
    register char c = getc(fp);	/* Do first getc before gettimeofday so	a */
				/*  delayed first read doesn't matter.	  */
				/* Delayed data can come from pipes like: */
				/*	zcat animation.Z | slowcat	  */

    if (gettimeofday(&next_due, NULL))	/* Keep next char due time here */
    {
	perror("gettimeofday() failed");
	exit(1);
    }

    time.tv_sec = 0;		/* Initialise to force gettimeofday */

    while (c != EOF)
    {
	if ((time.tv_sec < next_due.tv_sec) || /* Don't bother to get */
	    ((time.tv_sec == next_due.tv_sec) && /* time & wait when */
	     (time.tv_usec < next_due.tv_usec))) /* output is due */
	{
	    if (gettimeofday(&time, NULL)) /* Current time */
	    {
		perror("gettimeofday() failed");
		exit(1);
	    }
	    /*
	     * Calculate the number of microseconds to wait until the next
	     * character is due. This can be negative if the char is late.
	     */
	    if ((uwait = (next_due.tv_sec - time.tv_sec) * M +
		 next_due.tv_usec - time.tv_usec) > 0)
	    {
		fflush(stdout);		/* We have to wait anyway... */
		time.tv_sec = 0;
		time.tv_usec = uwait;
		
		if (select(0, NULL, NULL, NULL, &time) < 0)
		{
		    perror("select failed");
		    exit(1);
		}
	    }
	}

	putchar(c);
	if ((next_due.tv_usec += interval) >= M)
	{
	    next_due.tv_usec -= M;
	    ++next_due.tv_sec;
	}
	c = getc(fp);
    }
}
--
Snail:	David Hines,  Daresbury Lab,	UUCP:	D.Hines@daresbury
	Warrington,  WA4 4AD,  U.K.	JANET:	D.H...@uk.ac.daresbury
	('phone:  +44 925 603357)	Other:	D.H...@daresbury.ac.uk

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