Re: Help in using gsapi_set_stdio() to capture stdout into a memory buffer

"Joaquim Luis" <[email protected]> Thu, 17 Mar 2016 16:17:53 -0000

Newsgroups	gmane.comp.printing.ghostscript.devel
Organization	UALG
Message-ID	<op.yeg8v3crdbaoe8@macmarilu>

Ken & Chris

Thanks for your replies. Because Chris suggestions sent me to unfamiliar  
grounds it took me a bit to digest that. I've came out with a solution  
based on pipes that seam to work.

I'm using here the pbmraw device because it's a simple non compressed  
format so I know how big is the buffer and also because ultimately that's  
how I want the raster.

One question still, where can I learn about the 'bitrgb' device structure?


NOTE: the code file is attached, as it was in my first message.

Thanks

Joaquim

> On 16/03/16 01:13, Joaquim Luis wrote:
>> Hi,
>>
>> I am trying to learn how to capture the raster conversion of a PS file
>> into memory but it's not being easy.
>> The following example (adapted from one posted here before) correctly
>> prints in stdout a png version of the small PS embedded in code. I know
>> it's correct because I save it into a file I see it is. But my goal is
>> to save it in a memory buffer so, as an intermediate step, I wanted to
>> save it in file via gsapi_set_stdio.
>
> This is *known* not to work and there is, in fact, a bug open to that
> effect (with a summary of why it doesn't work):
>
> http://bugs.ghostscript.com/show_bug.cgi?id=694993
>
> The trouble is, without changing a fundamental assumption of the device
> API, it's unlikely to be possible.
>
> FWIW, your best solution would be to write your own device. If you are
> not doing high resolution or large page work, you could look at using
> the "display device".
>
> Lastly, a possible workable solution would be to use a named pipe: pass
> the named pipe to gs for output, and have your code read back from it -
> depending on the amount of buffering Windows does on named pipes, you
> might need to do some fiddling (maybe theads, maybe separate processes)
> to read as data is being written.... if it were me, I'd spawn a separate
> process for gs.
>
> Chris
> _______________________________________________
> gs-devel mailing list
> [email protected]
> http://ghostscript.com/cgi-bin/mailman/listinfo/gs-devel

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gstest.c (application/octet-stream, 3.5 KB)

#include <stdio.h>
#include <stdlib.h>

#include <io.h>
#include <fcntl.h>
#include <process.h>

#include "ierrors.h"
#include "iapi.h"

#ifdef _WIN32
#	define dup2 _dup2
#	define fileno _fileno
#	define close _close
#else
#include <unistd.h>
#endif

char *ps = "newpath\n"
"100 600 moveto 200 650 lineto 100 700 lineto\n"
"closepath\n"
"gsave\n"
"0.5 setgray\n"
"fill\n"
"grestore\n"
"4 setlinewidth\n"
"stroke\n"
"/Times-Roman findfont\n"
"18 scalefont\n"
"setfont\n"
"newpath\n"
"150 600 moveto\n"
"(Julia-Ghostscript in action) show\n"
"/csquare {\n"
   "newpath\n"
   "0 26 moveto\n"
   "0 1 rlineto\n"
   "1 0 rlineto\n"
   "0 -1 rlineto\n"
   "closepath\n"
   "setrgbcolor\n"
   "fill\n"
"} def\n"
"\n"
"20 20 scale\n"
"\n"
"1 5 translate\n"
"1 0 0 csquare\n"
"\n"
"1 0 translate\n"
"0 1 0 csquare\n"
"\n"
"1 0 translate\n"
"0 0 1 csquare\n"
"showpage";

void *gs_rasterize_free(char *img) {
	/* Free memory allocated in this file. Needed because the croos boundary dll on Windows */
	free(img);
}

/* stdio functions */
static int GSDLLCALL gsdll_stdin(void *instance, char *buf, int len) {
    return 0;
}

static int GSDLLCALL gsdll_stdout(void *instance, const char *str, int len) {
	//fprintf(stderr, "MERDA out\n");
    //fwrite(str, 1, len, fp);
    //fflush(fp);
    return len;
}

static int GSDLLCALL gsdll_stderr(void *instance, const char *str, int len) {
    fwrite(str, 1, len, stderr);
    fflush(stderr);
    return len;
}

int main(int argc, char *argv[]) {
	int GScode = 0, GSexitCode, n, l2, l3, n_rows, n_cols;
	int fd[2];
	char buf[1025], t[16] = { "" }, *img;
	void *GSinst;

	char *GSargs[] = {
		//argv[0], "-sDEVICE=pngalpha", "-dBATCH", "-dNOPAUSE", "-sOutputFile=-", "-q"
		//argv[0], "-sDEVICE=pbmraw", "-dBATCH", "-dNOPAUSE", "-sOutputFile=-", "-q -r300"
		"", "-sDEVICE=pbmraw", "-dBATCH", "-dNOPAUSE", "-sOutputFile=-", "-q -r300"
	};

    if ((GScode = gsapi_new_instance(&GSinst, NULL )) < 0 ) {
		fprintf(stderr, "Ghostscript gsapi_new_instance fail (%d)\n", GScode);
        exit(0);
    }

    gsapi_set_stdio(GSinst, gsdll_stdin, gsdll_stdout, gsdll_stderr);

	if ((GScode = gsapi_init_with_args(GSinst, 5, GSargs)) < 0) {
		fprintf(stderr, "Ghostscript gsapi_init_with_args fail (%d)\n", GScode);
        exit(0);
    }

#ifdef _WIN32
	_pipe(fd, 104857600000, O_BINARY);
#else
	pipe(fd);
#endif

	if (dup2(fd[1], fileno(stdout)) != 0) 
		return   2;
	close(fd[1]); 		// Close original write end of pipe 

    if (gsapi_run_string(GSinst, ps, 0, &GSexitCode) < 0 ) {
    	fprintf (stderr, "Error: Could not run gsapi_run_string()\n");
    }

	n = read(fd[0], buf, 3);							/* Consume first header line */
	while (read(fd[0], buf, 1) && buf[0] != '\n');		/* OK, by the end of this we are at the end of second header line*/
	n = 0;
	while (read(fd[0], buf, 1) && buf[0] != ' ')		/* Get string with number of columns from 3rth header line */
		t[n++] = buf[0];
	n_cols = atoi(t);
	n = 0;
	while (read(fd[0], buf, 1) && buf[0] != '\n')		/* Get string with number of rows from 3rth header line */
		t[n++] = buf[0];
	t[n] = '\0';										/* Make sure no character is left from previous usage */
	n_rows = atoi(t);

	img = malloc(n_rows * n_cols * 3);
	if ((n = read(fd[0], img, n_rows * n_cols * 3)) >= 0) {
		fprintf(stderr, "read %d bytes from the pipe:\n %s\n", n, buf);
	}
	else
		perror("read");

	fprintf (stderr, "Ghostscript gsapi_run_file OK\n");
}