1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>The Ghostscript Interpreter Application Programming Interface (API)</title>
<!-- $Id$ -->
<!-- Supercedes the API in DLL.htm -->
<link rel="stylesheet" type="text/css" href="gs.css" title="Ghostscript Style">
</head>
<body>
<!-- [1.0 begin visible header] ============================================ -->
<!-- [1.1 begin headline] ================================================== -->
<h1>The Ghostscript Interpreter Application Programming Interface (API)</h1>
<!-- [1.1 end headline] ==================================================== -->
<!-- [1.2 begin table of contents] ========================================= -->
<h2>Table of contents</h2>
<ul>
<li><a href="#API">What is the Ghostscript Interpreter API?</a>
<li><a href="#Exported_functions ">Exported functions</a>
<ul>
<li><a href="#revision"><b><tt>gsapi_revision</tt></b></a>
<li><a href="#new_instance"><b><tt>gsapi_new_instance</tt></b></a>
<li><a href="#delete_instance"><b><tt>gsapi_delete_instance</tt></b></a>
<li><a href="#set_stdio"><b><tt>gsapi_set_stdio</tt></b></a>
<li><a href="#set_poll"><b><tt>gsapi_set_poll</tt></b></a>
<li><a href="#set_display_callback"><b><tt>gsapi_set_display_callback</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_string_begin</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_string_continue</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_string_end</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_string_with_length</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_string</tt></b></a>
<li><a href="#init"><b><tt>gsapi_init_with_args</tt></b></a>
<li><a href="#run"><b><tt>gsapi_run_*</tt></b></a>
<li><a href="#exit"><b><tt>gsapi_exit</tt></b></a>
<li><a href="#set_visual_tracer"><b><tt>gsapi_set_visual_tracer</tt></b></a>
<li><a href="#return_codes">Return codes</a>
</ul>
<li><a href="#Example_usage">Example usage</a>
<li><a href="#stdio">Standard input and output</a>
<li><a href="#display">Display device</a>
</ul>
<!-- [1.2 end table of contents] =========================================== -->
<!-- [1.3 begin hint] ====================================================== -->
<p>For other information, see the <a href="Readme.htm">Ghostscript
overview</a>.
<p>
<b>WARNING:</b> The API described in this document is subject to changes in
future releases, possibly ones that are not backward compatible with what
is described here.
<!-- [1.3 end hint] ======================================================== -->
<hr>
<!-- [1.0 end visible header] ============================================== -->
<!-- [2.0 begin contents] ================================================== -->
<h2><a name="API"></a>What is the Ghostscript Interpreter API?</h2>
<p>
The Ghostscript interpreter can be built as a dynamic link library
(DLL) on the Windows or OS/2 platforms, as a shared object on the
Linux platform and as a framework on MacOS X.
With some changes, it could be built as a static library.
This document describes the Application Programming Interface (API)
for the Ghostscript interpreter library.
This should not be confused with the
<a href="Lib.htm">Ghostscript library</a> which provides a graphics
library but not the interpreter.
<p>
This supercedes the old <a href="DLL.htm">DLL</a> interface.
<p>
To provide the interface described in the
<a href="Use.htm">usage documentation</a>, a smaller independent
executable loads the DLL/shared object.
This executable must provide all the interaction with the windowing system,
including image windows and, if necessary, a text window.
<p>
The Ghostscript interpreter library's name and characteristics differ
for each platform:
<ul>
<li>The Win32 DLL <b><tt>gsdll32.dll</tt></b>
can be used by multiple programs simultaneously, but only once
within each process.
<li>The OS/2 DLL <b><tt>gsdll2.dll</tt></b> has
MULTIPLE NONSHARED data segments and can be called by multiple programs
simultaneously.
<li>The Linux shared object <b><tt>libgs.so</tt></b>
can be used by multiple programs simultaneously.
<li>The MacOS X <b><tt>Ghostscript.framework</tt></b> can also be used
by multiple applications at once.
</ul>
<p>
The source for the executable is in <b><tt>dw</tt></b>*.* (Windows),
<b><tt>dp</tt></b>*.* (OS/2) and <b><tt>dx</tt></b>*.* (Linux).
See these source files for examples of how to use the DLL. A similar
example for MacOS using the Carbon API is provided in <b><tt>dm</tt></b>*.*.
<p>
The source file <tt>dxmainc.c</tt> can also serve as an example of how to use the
framework shared component on MacOS X, providing the same command-line tool it does
on any linux, bsd or similar operating system. Just change the header includes to
use the Ghostscript namespace:
<blockquote><pre><tt>#include <Ghostscript/ierrors.h>
#include <Ghostscript/iapi.h></tt></pre></blockquote>
and link with:
<blockquote><pre><tt>cc -o gsc dxmainc.c -framework Ghostscript</tt></pre></blockquote>
To get a useable executable. <tt>Ghostscript.framework</tt> must be properly
installed in the search path for this to work.
<p>
At this stage, Ghostscript does not support multiple instances
of the interpreter within a single process.
<hr>
<h2><a name="Exported_functions"></a>Exported functions</h2>
<p>
The functions exported by the DLL/shared object are described
in the header file <a href="../src/iapi.h"><b><tt>iapi.h</tt></b></a>
and are summarised below. Omitted from the summary are
the calling convention (e.g. __stdcall), details of return
values and error handling.
<ul>
<li><b><tt>
int
<a href="#revision">gsapi_revision</a>
(gsapi_revision_t *pr, int len);
</tt></b>
<li><b><tt>
int
<a href="#new_instance">gsapi_new_instance</a>
(void **pinstance, void *caller_handle);
</tt></b>
<li><b><tt>
void
<a href="#delete_instance">gsapi_delete_instance</a>
(void *instance);
</tt></b>
<li><b><tt>
int
<a href="#set_stdio">gsapi_set_stdio</a>
(void *instance,
int(*stdin_fn)(void *caller_handle, char *buf, int len),
int(*stdout_fn)(void *caller_handle, const char *str, int len),
int(*stderr_fn)(void *caller_handle, const char *str, int len));
</tt></b>
<li><b><tt>
int
<a href="#set_poll">gsapi_set_poll</a>
(void *instance, int(*poll_fn)(void *caller_handle));
</tt></b>
<li><b><tt>
int
<a href="#set_display_callback">gsapi_set_display_callback</a>
(void *instance, display_callback *callback);
</tt></b>
<li><b><tt>
int
<a href="#init">gsapi_init_with_args</a>
(void *instance, int argc, char **argv);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_string_begin</a>
(void *instance, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_string_continue</a>
(void *instance,
const char *str, unsigned int length, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_string_end</a>
(void *instance, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_string_with_length</a>
(void *instance,
const char *str, unsigned int length, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_string</a>
(void *instance,
const char *str, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#run">gsapi_run_file</a>
(void *instance,
const char *file_name, int user_errors, int *pexit_code);
</tt></b>
<li><b><tt>
int
<a href="#exit">gsapi_exit</a>
(void *instance);
</tt></b>
<li><b><tt>
int
<a href="#set_visual_tracer">gsapi_set_visual_tracer</a>
(gstruct vd_trace_interface_s *I);
</tt></b>
</ul>
<h3><a name="revision"></a><b><tt>gsapi_revision()</tt></b></h3>
<blockquote>
This function returns the revision numbers and strings of the Ghostscript
interpreter library; you should call it before any other interpreter
library functions to make sure that the correct version of the
Ghostscript interpreter has been loaded.
<blockquote>
<pre>
typedef struct gsapi_revision_s {
const char *product;
const char *copyright;
long revision;
long revisiondate;
} gsapi_revision_t;
gsapi_revision_t r;
if (gsapi_revision(&r, sizeof(r)) == 0) {
if (r.revision < 650)
printf("Need at least Ghostscript 6.50");
}
else {
printf("revision structure size is incorrect");
}
</pre></blockquote>
</blockquote>
<h3><a name="new_instance"></a><b><tt>gsapi_new_instance()</tt></b></h3>
<blockquote>
Create a new instance of Ghostscript.
This instance is passed to most other gsapi functions.
The caller_handle will be provided to callback functions.
<b>At this stage, Ghostscript supports only one instance</b>.
</blockquote>
<h3><a name="delete_instance"></a><b><tt>gsapi_delete_instance()</tt></b></h3>
<blockquote>
Destroy an instance of Ghostscript.
Before you call this, Ghostscript must have finished.
If Ghostscript has been initialised, you must call
<b><tt>gsapi_exit</tt></b> before <b><tt>gsapi_delete_instance</tt></b>.
</blockquote>
<h3><a name="set_stdio"></a><b><tt>gsapi_set_stdio()</tt></b></h3>
<blockquote>
Set the callback functions for stdio
The stdin callback function should return the number of
characters read, 0 for EOF, or -1 for error.
The stdout and stderr callback functions should return
the number of characters written.
</blockquote>
<h3><a name="set_poll"></a><b><tt>gsapi_set_poll()</tt></b></h3>
<blockquote>
Set the callback function for polling.
This is used for handling window events or cooperative
multitasking. This function will only be called if
the Ghostscript interpreter was compiled with <b><tt>CHECK_INTERRUPTS</tt></b>
as described in <b><tt><a href="../src/gpcheck.h">gpcheck.h</a></tt></b>.
The polling function should return zero if all is well,
and return negative if it wants ghostscript to abort.
The polling function must be fast.
</blockquote>
<h3><a name="set_display_callback"></a><b><tt>gsapi_set_display_callback()</tt></b></h3>
<blockquote>
Set the callback structure for the <a href="#display">display</a>
device. If the <a href="#display">display</a> device is used,
this must be called after
<b><tt>gsapi_new_instance()</tt></b>
and before <b><tt>gsapi_init_with_args()</tt></b>.
See <b><tt><a href="../src/gdevdsp.h">gdevdsp.h</a></tt></b>
for more details.
</blockquote>
<h3><a name="init"></a><b><tt>gsapi_init_with_args()</tt></b></h3>
<blockquote>
Initialise the interpreter.
This calls <b><tt>gs_main_init_with_args()</tt></b> in
<b><tt><a href="../src/imainarg.c">imainarg.c</a></tt></b>.
See below for <a href="#return_codes">return codes</a>.
The arguments are the same as the "C" main function:
argv[0] is ignored and the user supplied arguments
are argv[1] to argv[argc-1].
</blockquote>
<h3><a name="run"></a><b><tt>gsapi_run_*()</tt></b></h3>
<blockquote>
The <b><tt>gsapi_run_*</tt></b> functions are like
<b><tt>gs_main_run_*</tt></b> except that the error_object is omitted.
If these functions return <= -100, either quit or a fatal
error has occured. You must call <b><tt>gsapi_exit()</tt></b> next.
The only exception is <b><tt>gsapi_run_string_continue()</tt></b>
which will return <b><tt>e_NeedInput</tt></b> if all is well.
See below for <a href="#return_codes">return codes</a>.
<p>
The address passed in <b><tt>pexit_code</tt></b> will be used to return the
exit code for the interpreter in case of a quit or fatal error. The
<b><tt>user_errors</tt></b> argument is normally set to zero to indicate that
errors should be handled through the normal mechanisms within the
interpreted code. If set to a negative value, the functions will return
an error code directly to the caller, bypassing the interpreted
language. The interpreted language's error handler is bypassed, regardless of
<b><tt>user_errors</tt></b> parameter, for the <b><tt>e_interrupt</tt></b>
generated when <a href="#set_poll">the polling callback</a> returns a negative
value. A positive <b><tt>user_errors</tt></b> is treated the same as zero.
<p>
There is a 64 KB length limit on any buffer submitted to a
<b><tt>gsapi_run_*</tt></b> function for processing. If you have more
than 65535 bytes of input then you must split it into smaller
pieces and submit each in a separate
<b><tt>gsapi_run_string_continue()</tt></b> call.
</blockquote>
<h3><a name="exit"></a><b><tt>gsapi_exit()</tt></b></h3>
<blockquote>
Exit the interpreter.
This must be called on shutdown if <b><tt>gsapi_init_with_args()</tt></b>
has been called, and just before <b><tt>gsapi_delete_instance()</tt></b>.
</blockquote>
<h3><a name="set_visual_tracer"></a><b><tt>gsapi_set_visual_tracer()</tt></b></h3>
<blockquote>
Pass visual tracer interface block to Ghostscript.
See <a href="Lib.htm#Visual_trace"><b><tt>Lib.htm</tt></b></a> for reference about
the interface block structure.
This function is useful for debug clients only. Release clients must not call it.
</blockquote>
<h3><a name="return_codes"></a>Return codes</h3>
<p>
The <b><tt>gsapi_init_with_args</tt></b>, <b><tt>gsapi_run_*</tt></b> and
<b><tt>gsapi_exit</tt></b> functions return an integer code.
<p>
<table width="80%" align="center" cellpadding=0 cellspacing=0>
<tr><th colspan=3 bgcolor="#CCCC00"><hr><font size="+1">Return codes from <b><tt>gsapi_*()</tt></b></font><hr>
<tr valign=bottom>
<th align=left>Code
<td>
<th align=left>Status
<tr> <td colspan=3><hr>
<tr valign=top> <td align=left>0
<td>
<td>No errors
<tr valign=top> <td align=left>e_Quit
<td>
<td>"<b><tt>quit</tt></b>" has been executed.
This is not an error.
<b><tt>gsapi_exit()</tt></b> must be called next.
<tr valign=top> <td align=left>e_interrupt
<td>
<td><a href="#set_poll">The polling callback function</a>
returned a negative value, requesting Ghostscript to abort.
<tr valign=top> <td align=left>e_NeedInput
<td>
<td>More input is needed by
<b><tt>gsapi_run_string_continue()</tt></b>.
This is not an error.
<tr valign=top> <td align=left>e_Info
<td>
<td>"<b><tt>gs -h</tt></b>" has been executed.
This is not an error.
<b><tt>gsapi_exit()</tt></b> must be called next.
<tr valign=top> <td align=left>< 0
<td>
<td>Error
<tr valign=top> <td align=left><= -100
<td>
<td>Fatal error.
<b><tt>gsapi_exit()</tt></b> must be called next.
</table>
</blockquote>
<p>
The <b><tt>gsapi_run_*()</tt></b> functions do not flush stdio.
If you want to see output from Ghostscript you
must do this explicitly as shown in the example below.
<p>
When executing a string with <b><tt>gsapi_run_string_*()</tt></b>,
<b><tt>currentfile</tt></b> is the input from the string.
Reading from <b><tt>%stdin</tt></b> uses the stdin callback.
</blockquote>
<h2><a name="Example_usage"></a>Example Usage</h2>
Some overly simple examples of using the Ghostscript interpreter library
are below. Some more examples including other programming languages
may be found at
<a href="http://www.cs.wisc.edu/~ghost/doc/gsapi.htm">
http://www.cs.wisc.edu/~ghost/doc/gsapi.htm</a>.
<p>To use try out these examples in a development environment like Microsoft's
developer tools or Metrowerks Codewarrior, create a new project, save the example
source code as a <tt>.c</tt> file and add it, along with the Ghostscript dll or shared
library. You will also need to make sure the Ghostscript headers are available, either
by adding their location (the <tt>src</tt> directory in the Ghostscript source
distribution) to the project's search path, or by copying ierrors.h and iapi.h into the
same directory as the example source.</p>
<h3>Example 1</h3>
<pre>
/* Example of using GS DLL as a ps2pdf converter. */
#if defined(_WIN32) && !defined(_Windows)
# define _Windows
#endif
#ifdef _Windows
/* add this source to a project with gsdll32.dll, or compile it directly with:
* cl -D_Windows -Isrc -Febin\ps2pdf.exe ps2pdf.c bin\gsdll32.lib
*/
# include <windows.h>
# define GSDLLEXPORT __declspec(dllimport)
#endif
#include "ierrors.h"
#include "iapi.h"
void *minst;
int main(int argc, char *argv[])
{
int code, code1;
const char * gsargv[10];
int gsargc;
gsargv[0] = "ps2pdf"; /* actual value doesn't matter */
gsargv[1] = "-dNOPAUSE";
gsargv[2] = "-dBATCH";
gsargv[3] = "-dSAFER";
gsargv[4] = "-sDEVICE=pdfwrite";
gsargv[5] = "-sOutputFile=out.pdf";
gsargv[6] = "-c";
gsargv[7] = ".setpdfwrite";
gsargv[8] = "-f";
gsargv[9] = "input.ps";
gsargc=10;
code = gsapi_new_instance(&minst, NULL);
if (code < 0)
return 1;
code = gsapi_init_with_args(minst, gsargc, gsargv);
code1 = gsapi_exit(minst);
if ((code == 0) || (code == e_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == e_Quit))
return 0;
return 1;
}
</pre>
<h3>Example 2</h3>
<pre>
/* Similar to command line gs */
#if defined(_WIN32) && !defined(_Windows)
# define _Windows
#endif
#ifdef _Windows
/* Compile directly with:
* cl -D_Windows -Isrc -Febin\gstest.exe gstest.c bin\gsdll32.lib
*/
# include <windows.h>
# define GSDLLEXPORT __declspec(dllimport)
#endif
#include <stdio.h>
#include "ierrors.h"
#include "iapi.h"
/* stdio functions */
static int GSDLLCALL
gsdll_stdin(void *instance, char *buf, int len)
{
int ch;
int count = 0;
while (count < len) {
ch = fgetc(stdin);
if (ch == EOF)
return 0;
*buf++ = ch;
count++;
if (ch == '\n')
break;
}
return count;
}
static int GSDLLCALL
gsdll_stdout(void *instance, const char *str, int len)
{
fwrite(str, 1, len, stdout);
fflush(stdout);
return len;
}
static int GSDLLCALL
gsdll_stderr(void *instance, const char *str, int len)
{
fwrite(str, 1, len, stderr);
fflush(stderr);
return len;
}
void *minst;
const char start_string[] = "systemdict /start get exec\n";
int main(int argc, char *argv[])
{
int code, code1;
int exit_code;
code = gsapi_new_instance(&minst, NULL);
if (code < 0)
return 1;
gsapi_set_stdio(minst, gsdll_stdin, gsdll_stdout, gsdll_stderr);
code = gsapi_init_with_args(minst, argc, argv);
if (code == 0)
code = gsapi_run_string(minst, start_string, 0, &exit_code);
code1 = gsapi_exit(minst);
if ((code == 0) || (code == e_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == e_Quit))
return 0;
return 1;
}
</pre>
<h3>Example 3</h3>
Replace main() in either of the above with the following code,
showing how you can feed Ghostscript piecemeal:
<pre>
const char *command = "1 2 add == flush\n";
int main(int argc, char *argv[])
{
int code, code1;
int exit_code;
code = gsapi_new_instance(&minst, NULL);
if (code < 0)
return 1;
code = gsapi_init_with_args(minst, argc, argv);
if (code == 0) {
gsapi_run_string_begin(minst, 0, &exit_code);
gsapi_run_string_continue(minst, command, strlen(command), 0, &exit_code);
gsapi_run_string_continue(minst, "qu", 2, 0, &exit_code);
gsapi_run_string_continue(minst, "it", 2, 0, &exit_code);
gsapi_run_string_end(minst, 0, &exit_code);
}
code1 = gsapi_exit(minst);
if ((code == 0) || (code == e_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == e_Quit))
return 0;
return 1;
}
</pre>
<h3>Example 4</h3>
When feeding Ghostscript piecemeal buffers, one can use the normal
operators to configure things and invoke library routines. For example,
to parse a PDF file one could say:
<pre>
code = gsapi_run_string(minst, "(example.pdf) .runlibfile", 0, &exit_code);
</pre>
and Ghostscript would open and process the file named "example.pdf" as
if it had been passed as an argument to
<b><tt>gsapi_init_with_args()</tt></b>.
<h2><a name="Multiple_threads"></a>Multiple threads</h2>
The Ghostscript library should have been compiled with a
thread safe run time library.
Synchronisation of threads is entirely up to the caller.
The exported <a href="#Exported_functions "><b><tt>gsapi_*()</tt></b></a>
functions must be called from one thread only.
<h2><a name="stdio"></a>Standard input and output</h2>
<p>
When using the Ghostscript interpreter library interface, you have a
choice of two standard input/output methods.
<ul>
<li>If you do nothing, the "C" stdio will be used.
<li>If you use <b><tt>gsapi_set_stdio()</tt></b>, all stdio will
be redirected to the callback functions you provide.
This would be used in a graphical user interface environment
where stdio is not available, or where you wish to process
Ghostscript input or output.
</ul>
<p>
The callback functions are described in
<a href="../src/iapi.h"><b><tt>iapi.h</tt></b></a>.
<h2><a name="display"></a>Display device</h2>
<p>
The <b><tt>display</tt></b> device is available for use with
the Ghostscript interpreter library. This is described in the file
<b><tt><a href="../src/gdevdsp.h">gdevdsp.h</a></tt></b>.
This device provides you with access to the raster output of
Ghostscript. It is your responsibility to copy this raster
to a display window or printer.
<p>
To use this device, you must provide a callback structure
with addresses of a number of callback functions.
The address of the callback structure is provided using
<b><tt>gsapi_set_display_callback()</tt></b>.
This must be called after
<b><tt>gsapi_new_instance()</tt></b>
and before
<b><tt>gsapi_init_with_args()</tt></b>.
<p>
The callbacks are for device open, close, resize, sync, page,
memory allocation and updating.
Each callback function contains a handle can be set using
<blockquote>
-dDisplayHandle=1234
</blockquote>
<p>
The device raster format can be configured using
<blockquote>
-dDisplayFormat=NNNN
</blockquote>
Options include
<ul>
<li> native, gray, RGB, CMYK or separation color spaces.
<li> alpha byte (ignored).
<li> 1 to 16 bits/component.
<li> bigendian (RGB) or littleendian (BGR) order.
<li> top first or bottom first raster.
<li> 16 bits/pixel with 555 or 565 bitfields.
</ul>
The format values are described in
<b><tt><a href="../src/gdevdsp.h">gdevdsp.h</a></tt></b>.
The format is flexible enough to support common Windows, OS/2, Linux
and Mac raster formats. To select the display device with a
Windows 24-bit RGB raster:
<pre>
char **nargv;
char arg1[64];
char arg2[64];
char arg3[64];
code = gsapi_new_instance(&minst, NULL);
gsapi_set_stdio(minst, gsdll_stdin, gsdll_stdout, gsdll_stderr);
code = gsapi_set_display_callback(minst, &display_callback);
sprintf(arg1, "-sDEVICE=display");
sprintf(arg2, "-dDisplayHandle=%d", 0);
sprintf(arg3, "-dDisplayFormat=%d",
DISPLAY_COLORS_RGB | DISPLAY_ALPHA_NONE | DISPLAY_DEPTH_8 |
DISPLAY_LITTLEENDIAN | DISPLAY_BOTTOMFIRST);
nargv = (char **)malloc((argc + 4) * sizeof(char *));
nargv[0] = argv[0];
nargv[1] = arg1;
nargv[2] = arg2;
nargv[3] = arg3;
memcpy(nargv + 4, argv + 1, argc * sizeof(char *));
argc += 3;
code = gsapi_init_with_args(minst, argc, nargv);
</pre>
<p>
The display device provides you with the address and size of the
raster using the <b><tt>display_size()</tt></b> callback.
You are then responsible for displaying this raster.
Some examples are in
<b><tt><a href="../src/dwmain.c">dwmain.c</a></tt></b> (Windows),
<b><tt><a href="../src/dpmain.c">dpmain.c</a></tt></b> (OS/2) and
<b><tt><a href="../src/dxmain.c">dxmain.c</a></tt></b> (X11/Linux), and
<b><tt><a href="../src/dmmain.c">dmmain.c</a></tt></b> (MacOS Classic or Carbon).
<p>
On some platforms, the calling convention for the display device callbacks in
<b><tt><a href="../src/gdevdsp.h">gdevdsp.h</a></tt></b>
is not the same as the exported
<a href="#Exported_functions "><b><tt>gsapi_*()</tt></b></a>
functions in <a href="../src/iapi.h"><b><tt>iapi.h</tt></b></a>.
<p>
<!-- [2.0 end contents] ==================================================== -->
<!-- [3.0 begin visible trailer] =========================================== -->
<hr>
<p>
<small>Copyright © 2000-2006 artofcode LLC. All rights reserved.</small>
<p>
This software is provided AS-IS with no warranty, either express or
implied.
This software is distributed under license and may not be copied, modified
or distributed except as expressly authorized under the terms of that
license. Refer to licensing information at http://www.artifex.com/
or contact Artifex Software, Inc., 7 Mt. Lassen Drive - Suite A-134,
San Rafael, CA 94903, U.S.A., +1(415)492-9861, for further information.
<p>
<small>Ghostscript version 8.57, 11 May 2007
<!-- [3.0 end visible trailer] ============================================= -->
</body>
</html>
|
