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
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
|
<!doctype html>
<html lang="en">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<meta name="viewport" content="user-scalable=yes, initial-scale=1, width=device-width">
<link href="https://fonts.googleapis.com/css?family=Source+Sans+Pro:200,200i,300,300i,400,400i,600,600i,700,700i,900,900i" rel="stylesheet">
<link rel="shortcut icon" type="image/png" href="images/favicon.png">
<title>The Ghostscript Interpreter Application Programming Interface (API)</title>
<link href="default.css" rel="stylesheet" type="text/css">
</head>
<body>
<header><a href="index.html"><h1>Ghostscript documentation</h1></a><a href="Search.htm" aria-label="Search" id="searchSite"><div class="search"></div></a></header>
<main>
<article>
<div class="outer">
<div class="inner">
<!--START EDITING HERE-->
<h1>API</h1>
<h2><a name="toc"></a>Table of contents</h2>
<ul class="toc">
<li><a href="#API">What is the Ghostscript Interpreter API?</a></li>
<li><a href="#Exported_functions ">Exported functions</a></li>
<li>
<ul>
<li><a href="#revision"><code>gsapi_revision</code></a></li>
<li><a href="#new_instance"><code>gsapi_new_instance</code></a></li>
<li><a href="#delete_instance"><code>gsapi_delete_instance</code></a></li>
<li><a href="#set_stdio_with_handle"><code>gsapi_set_stdio_with_handle</code></a></li>
<li><a href="#set_stdio"><code>gsapi_set_stdio</code></a></li>
<li><a href="#set_poll_with_handle"><code>gsapi_set_poll_with_handle</code></a></li>
<li><a href="#set_poll"><code>gsapi_set_poll</code></a></li>
<li><a href="#set_display_callback"><code>gsapi_set_display_callback</code></a></li>
<li><a href="#register_callout"><code>gsapi_register_callout</code></a></li>
<li><a href="#deregister_callout"><code>gsapi_deregister_callout</code></a></li>
<li><a href="#set_arg_encoding"><code>gsapi_set_arg_encoding</code></a></li>
<li><a href="#get_default_device_list"><code>gsapi_get_default_device_list</code></a></li>
<li><a href="#set_default_device_list"><code>gsapi_set_default_device_list</code></a></li>
<li><a href="#run"><code>gsapi_run_string_begin</code></a></li>
<li><a href="#run"><code>gsapi_run_string_continue</code></a></li>
<li><a href="#run"><code>gsapi_run_string_end</code></a></li>
<li><a href="#run"><code>gsapi_run_string_with_length</code></a></li>
<li><a href="#run"><code>gsapi_run_string</code></a></li>
<li><a href="#run"><code>gsapi_run_file</code></a></li>
<li><a href="#init"><code>gsapi_init_with_args</code></a></li>
<li><a href="#exit"><code>gsapi_exit</code></a></li>
<li><a href="#set_param"><code>gsapi_set_param</code></a></li>
<li><a href="#get_param"><code>gsapi_get_param</code></a></li>
<li><a href="#enumerate_params"><code>gsapi_enumerate_params</code></a></li>
<li><a href="#add_control_path"><code>gsapi_add_control_path</code></a></li>
<li><a href="#remove_control_path"><code>gsapi_remove_control_path</code></a></li>
<li><a href="#purge_control_paths"><code>gsapi_purge_control_paths</code></a></li>
<li><a href="#activate_path_control"><code>gsapi_activate_path_control</code></a></li>
<li><a href="#is_path_control_active"><code>gsapi_is_path_control_active</code></a></li>
<li><a href="#add_fs"><code>gsapi_add_fs</code></a></li>
<li><a href="#remove_fs"><code>gsapi_remove_fs</code></a></li>
<li><a href="#return_codes">Return codes</a></li>
<li><a href="#gsapi_fs_t">gsapi_fs_t</a></li>
<li><a href="#callout">Callouts</a></li>
</ul>
</li>
<li><a href="#Example_usage">Example usage</a></li>
<li><a href="#stdio">Standard input and output</a></li>
<li><a href="#display">Display device</a></li>
</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>
<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.</p>
<!-- [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 Microsoft Windows, as a shared object on the
Linux, Unix and MacOS X platforms. 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>
<p>
This supercedes the old <a href="DLL.htm">DLL</a> interface.</p>
<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>
<p>
The Ghostscript interpreter library's name and characteristics differ
for each platform:</p>
<ul>
<li>The Win32 DLL <code>gsdll32.dll</code>
can be used by multiple programs simultaneously, but only once
within each process.</li>
<li>The OS/2 DLL <code>gsdll2.dll</code> has
MULTIPLE NONSHARED data segments and can be called by multiple programs
simultaneously.</li>
<li>The Linux shared object <code>libgs.so</code>
can be used by multiple programs simultaneously.</li>
</ul>
<p>
The source for the executable is in <code>dw</code>*.* (Windows),
<code>dp</code>*.* (OS/2) and <code>dx</code>*.* (Linux/Unix).
See these source files for examples of how to use the DLL.</p>
<p>
The source file <tt>dxmainc.c</tt> can also serve as an example of how to use the
shared library component on MacOS X, providing the same command-line tool it does
on any linux, bsd or similar operating system.</p>
<p>
At this stage, Ghostscript does not support multiple instances
of the interpreter within a single process.</p>
<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="../psi/iapi.h"><code>iapi.h</code></a>
and are summarised below. Omitted from the summary are
the calling convention (e.g. __stdcall), details of return
values and error handling.</p>
<ul>
<li><code>
int
<a href="#revision">gsapi_revision</a>
(gsapi_revision_t *pr, int len);
</code></li>
<li><code>
int
<a href="#new_instance">gsapi_new_instance</a>
(void **pinstance, void *caller_handle);
</code></li>
<li><code>
void
<a href="#delete_instance">gsapi_delete_instance</a>
(void *instance);
</code></li>
<li><code>
int
<a href="#set_stdio_with_handle">gsapi_set_stdio_with_handle</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),
void *caller_handle);
</code></li>
<li><code>
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));
</code></li>
<li><code>
int
<a href="#set_poll_with_handle">gsapi_set_poll_with_handle</a>
(void *instance, int(*poll_fn)(void *caller_handle), void *caller_handle);
</code></li>
<li><code>
int
<a href="#set_poll">gsapi_set_poll</a>
(void *instance, int(*poll_fn)(void *caller_handle));
</code></li>
<li><code>
int
<a href="#set_display_callback">gsapi_set_display_callback</a>
(void *instance, display_callback *callback);
</code></li>
<li><code>
int
<a href="#register_callout">gsapi_register_callout</a>
(void *instance, gs_callout callout, void *callout_handle);
</code></li>
<li><code>
void
<a href="#deregister_callout">gsapi_deregister_callout</a>
(void *instance, gs_callout callout, void *callout_handle);
</code></li>
<li><code>
int
<a href="#set_arg_encoding">gsapi_set_arg_encoding</a>
(void *instance, int encoding);
</code></li>
<li><code>
int
<a href="#get_default_device_list">gsapi_get_default_device_list</a>(void *instance, char **list, int *listlen);
</code></li>
<li><code>
int
<a href="#set_default_device_list">gsapi_set_default_device_list</a>(void *instance, const char *list, int listlen);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_string_begin</a>
(void *instance, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_string_continue</a>
(void *instance,
const char *str, unsigned int length, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_string_end</a>
(void *instance, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_string_with_length</a>
(void *instance,
const char *str, unsigned int length, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_string</a>
(void *instance,
const char *str, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#run">gsapi_run_file</a>
(void *instance,
const char *file_name, int user_errors, int *pexit_code);
</code></li>
<li><code>
int
<a href="#init">gsapi_init_with_args</a>
(void *instance, int argc, char **argv);
</code></li>
<li><code>
int
<a href="#exit">gsapi_exit</a>
(void *instance);
</code></li>
<li><code>
int
<a href="#set_param">gsapi_set_param</a>(void *instance, const char *param, const void *value, gs_set_param_type type);
</code></li>
<li><code>
int
<a href="#get_param">gsapi_get_param</a>(void *instance, const char *param, void *value, gs_set_param_type type);
</code></li>
<li><code>
int
<a href="#enumerate_params">gsapi_enumerate_params</a>(void *instance, void **iter, const char **key, gs_set_param_type *type);
</code></li>
<li><code>
int
<a href="#add_control_path">gsapi_add_control_path</a>(void *instance, int type, const char *path);
</code></li>
<li><code>
int
<a href="#remove_control_path">gsapi_remove_control_path</a>(void *instance, int type, const char *path);
</code></li>
<li><code>
void
<a href="#purge_control_paths">gsapi_purge_control_paths</a>(void *instance, int type);
</code></li>
<li><code>
void
<a href="#activate_path_control">gsapi_activate_path_control</a>(void *instance, int enable);
</code></li>
<li><code>
int
<a href="#is_path_control_active">gsapi_is_path_control_active</a>(void *instance);
</code></li>
<li><code>
int
<a href="#add_fs">gsapi_add_fs</a>
(void *instance,
gsapi_fs_t *fs, void *secret);
</code></li>
<li><code>
void
<a href="#remove_fs">gsapi_remove_fs</a>
(void *instance,
gsapi_fs_t *fs, void *secret);
</code></li>
</ul>
<h3><a name="revision"></a><code>gsapi_revision()</code></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><code>gsapi_new_instance()</code></h3>
<blockquote>
Create a new instance of Ghostscript.
This instance is passed to most other gsapi functions.
The caller_handle is the default value that will be provided to callback functions.
<b>Unless Ghostscript has been compiled with the </code>GS_THREADSAFE</code>
define, only one instance at a time is supported.</b>
<p>Historically, Ghostscript has only supported a single instance; any
attempt to create more than one at a time would result in gsapi_new_instance
returning an error. Experimental work has been done to lift this
restriction; if Ghostscript is compiled with the GS_THREADSAFE define
then multiple concurrent instances are permitted.</p>
<p>While the core Ghostscript devices are believed to be thread safe
now, certain devices are known not to be (particularly the contrib
devices). The makefiles currently make no attempt to exclude these
from builds. If you enable GS_THREADSAFE then you should check to ensure
that you do not rely on such devices (check for global variable use).</p>
<p>
The first parameter, is a pointer to an opaque pointer ("<code>void **</code>").
The opaque pointer ("<code>void *</code>") must be initialised to <code>NULL</code> before
the call to <code>gsapi_new_instance()</code>. See <a href="#Example_1">Example 1</a>.
</blockquote>
<h3><a name="delete_instance"></a><code>gsapi_delete_instance()</code></h3>
<blockquote>
Destroy an instance of Ghostscript.
Before you call this, Ghostscript must have finished.
If Ghostscript has been initialised, you must call
<code>gsapi_exit</code> before <code>gsapi_delete_instance</code>.
</blockquote>
<h3><a name="set_stdio_with_handle"></a><code>gsapi_set_stdio_with_handle()</code></h3>
<blockquote>
<p>Set the callback functions for stdio, together with the
handle to use in the callback functions.
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.
<p><b>NOTE:</b> These callbacks do not affect output device I/O when
using "<code>%stdout</code>" as the output file. In that
case, device output will still be directed to the process "stdout"
file descriptor, not to the stdio callback.
</blockquote>
<h3><a name="set_stdio"></a><code>gsapi_set_stdio()</code></h3>
<blockquote>
<p>Set the callback functions for stdio. The handle used
in the callbacks will be taken from the value passed
to <code><a href="#new_instance">gsapi_new_instance</a></code>. Otherwise the behaviour of this
function matches <code><a href="#set_stdio_with_handle">gsapi_set_stdio_with_handle</a></code>.
</blockquote>
<h3><a name="set_poll_with_handle"></a><code>gsapi_set_poll_with_handle()</code></h3>
<blockquote>
Set the callback function for polling, together with the handle to pass
to the callback function. This function will only be called if
the Ghostscript interpreter was compiled with <code>CHECK_INTERRUPTS</code>
as described in <code><a href="../base/gpcheck.h">gpcheck.h</a></code>.
<p>
The polling function should return zero if all is well, and return
negative if it wants ghostscript to abort. This is often
used for checking for a user cancel. This can also be used for
handling window events or cooperative multitasking.</p>
<p>
The polling function is called very frequently during interpretation and
rendering so it must be fast. If the function is slow, then using a counter
to return 0 immediately some number of times can be used to reduce the
performance impact.</p>
</blockquote>
<h3><a name="set_poll"></a><code>gsapi_set_poll()</code></h3>
<blockquote>
Set the callback function for polling. The handle passed to the
callback function will be taken from the handle passed to
<code><a href="#new_instance">gsapi_new_instance</a></code>.
Otherwise the behaviour of this function matches
<code><a href="#set_poll_with_handle">gsapi_set_poll_with_handle</a></code>.
</blockquote>
<h3><a name="set_display_callback"></a><code>gsapi_set_display_callback()</code></h3>
<blockquote>
<b>This call is deprecated; please use
<code><a href="#register_callout">gsapi_register_callout</a></code>
to register a <a href="#callout">callout</a> handler for the
<a href="#display">display</a> device in preference.</b>
Set the callback structure for the <a href="#display">display</a>
device. The handle passed in the callback functions is taken from
the <code>DisplayHandle</code> parameter (or NULL if there is no
such parameter). If the <a href="#display">display</a> device is used,
this must be called after
<code>gsapi_new_instance()</code>
and before <code>gsapi_init_with_args()</code>.
See <code><a href="../devices/gdevdsp.h">gdevdsp.h</a></code>
for more details.
</blockquote>
<h3><a name="register_callout"></a><code>gsapi_register_callout()</code></h3>
<blockquote>
<p>This call registers a <code><a href="#callout">callout</a></code>
handler.</p>
</blockquote>
<h3><a name="deregister_callout"></a><code>gsapi_deregister_callout()</code></h3>
<blockquote>
<p>This call deregisters a <code><a href="#callout">callout</a></code> handler
previously registered with <code><a href="#register_callout">gsapi_register_callout</a></code>.
All three arguments must match exactly for the callout handler to
be deregistered.</p>
</blockquote>
<h3><a name="set_arg_encoding"></a><code>gsapi_set_arg_encoding()</code></h3>
<blockquote>
Set the encoding used for the interpretation of all subsequent args
supplied via the gsapi interface on this instance. By default we
expect args to be in encoding 0 (the 'local' encoding for this OS).
On Windows this means "the currently selected codepage". On Linux this
typically means utf8. This means that omitting to call this function
will leave Ghostscript running exactly as it always has. Please note
that use of the 'local' encoding is now deprecated and should be
avoided in new code.
This must be called after <code>gsapi_new_instance()</code>
and before <code>gsapi_init_with_args()</code>.
</blockquote>
<h3><a name="set_default_device_list"></a><code>set_default_device_list()</code></h3>
<blockquote>
Set the string containing the list of default device names,
for example "display x11alpha x11 bbox". Allows the calling
application to influence which device(s) gs will try, in order,
in it's selection of the default device.
This must be called after <code>gsapi_new_instance()</code>
and before <code>gsapi_init_with_args()</code>.
</blockquote>
<h3><a name="get_default_device_list"></a><code>get_default_device_list()</code></h3>
<blockquote>
Returns a pointer to the current default device string.
This must be called after <code>gsapi_new_instance()</code>
and before <code>gsapi_init_with_args()</code>.
</blockquote>
<h3><a name="init"></a><code>gsapi_init_with_args()</code></h3>
<blockquote>
Initialise the interpreter.
This calls <code>gs_main_init_with_args()</code> in
<code><a href="../psi/imainarg.c">imainarg.c</a></code>.
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><code>gsapi_run_*()</code></h3>
<blockquote>
The <code>gsapi_run_*</code> functions are like
<code>gs_main_run_*</code> except that the error_object is omitted.
If these functions return <= -100, either quit or a fatal
error has occured. You must call <code>gsapi_exit()</code> next.
The only exception is <code>gsapi_run_string_continue()</code>
which will return <code>gs_error_NeedInput</code> if all is well.
See below for <a href="#return_codes">return codes</a>.
<p>
The address passed in <code>pexit_code</code> will be used to return the
exit code for the interpreter in case of a quit or fatal error. The
<code>user_errors</code> 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
<code>user_errors</code> parameter, for the <code>gs_error_interrupt</code>
generated when <a href="#set_poll">the polling callback</a> returns a negative
value. A positive <code>user_errors</code> is treated the same as zero.</p>
<p>
There is a 64 KB length limit on any buffer submitted to a
<code>gsapi_run_*</code> 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
<code>gsapi_run_string_continue()</code> call.</p>
</blockquote>
<h3><a name="exit"></a><code>gsapi_exit()</code></h3>
<blockquote>
Exit the interpreter.
This must be called on shutdown if <code>gsapi_init_with_args()</code>
has been called, and just before <code>gsapi_delete_instance()</code>.
</blockquote>
<h3><a name="set_param"></a><code>gsapi_set_param()</code></h3>
<blockquote>
Set a parameter.
Broadly, this is equivalent to setting a parameter using <code>-d</code>, <code>-s</code> or <code>-p</code> on the command line. This call cannot be made during a <code>run_string</code> operation.
<p>
Parameters in this context are not the same as 'arguments' as processed by <code>gsapi_init_with_args</code>, but often the same thing can be achieved. For example, with <code>gsapi_init_with_args</code>, we can pass "<code>-r200</code>" to change the resolution. Broadly the same thing can be achieved by using <code>gsapi_set_param</code> to set a parsed value of "<code><</HWResolution [ 200.0 200.0 ]>></code>".
<p>
Note, that internally, when we set a parameter, we perform an <code>initgraphics</code> operation. This means that using <code>set_param</code> other than at the start of a page is likely to give unexpected results.
<p>Further, note that attempting to set a parameter that the device does not recognise will be silently ignored, and that parameter will not be found in subsequent <code>gsapi_get_param</code> calls.
<p>The <code>type</code> argument dictates the kind of object that <code>value</code> points to:
<pre><code>typedef enum {
gs_spt_invalid = -1,
gs_spt_null = 0, /* void * is NULL */
gs_spt_bool = 1, /* void * is a pointer to an int (0 false,
* non-zero true). */
gs_spt_int = 2, /* void * is a pointer to an int */
gs_spt_float = 3, /* void * is a float * */
gs_spt_name = 4, /* void * is a char * */
gs_spt_string = 5, /* void * is a char * */
gs_spt_long = 6, /* void * is a long * */
gs_spt_i64 = 7, /* void * is an int64_t * */
gs_spt_size_t = 8, /* void * is a size_t * */
gs_spt_parsed = 9, /* void * is a pointer to a char * to be parsed */
/* Setting a typed param causes it to be instantly fed to to the
* device. This can cause the device to reinitialise itself. Hence,
* setting a sequence of typed params can cause the device to reset
* itself several times. Accordingly, if you OR the type with
* gs_spt_more_to_come, the param will held ready to be passed into
* the device, and will only actually be sent when the next typed
* param is set without this flag (or on device init). Not valid
* for get_typed_param. */
gs_spt_more_to_come = 1<<31
} gs_set_param_type;
</code></pre>
<p>Combining a type value by ORRing it with the <code>gs_spt_more_to_come</code> flag will cause the <code>set_param</code> operation to be queued internally, but not actually be sent to the device. Thus a series of <code>set_param</code> operations can be queued, for example as below:
<pre>
int code = gsapi_set_param(instance,
"HWResolution",
"[300 300]",
gs_spt_parsed | gs_spt_more_to_come);
if (code >= 0) {
int i = 1;
code = gsapi_set_param(instance,
"FirstPage",
&i,
gs_spt_int | gs_spt_more_to_come);
}
if (code >= 0) {
int i = 3;
code = gsapi_set_param(instance,
"DownScaleFactor",
&i,
gs_spt_int);
}
</pre>
<p>This enables a series of set operations to be performed 'atomically'. This can be useful for performance, in that any reconfigurations to the device (such as page size changes or memory reallocations) will only happen when all the parameters are sent, rather than potentially each time each one is sent.
</blockquote>
<h3><a name="get_param"></a><code>gsapi_get_param()</code></h3>
<blockquote>
Get a parameter.
Retrieve the current value of a parameter.
<p>If an error occurs, the return value is negative. Otherwise the return value is the number of bytes required for storage of the value. Call once with <code>value = NULL</code> to get the number of bytes required, then call again with <code>value</code> pointing to at least the required number of bytes where the value will be copied out. Note that the caller is required to know the type of value in order to get it. For all types other than <code>string</code>, <code>name</code>, and <code>parsed</code> knowing the type means you already know the size required.
<p>
This call retrieves parameters/values that have made it to the device. Thus, any values set using the <code>gs_spt_more_to_come</code> without a following call without that flag will not be retrieved. Similarly, attempting to get a parameter before <code>gsapi_init_with_args</code> has been called will not list any, even if <code>gsapi_set_param</code> has been used.
<p>
Attempting to read a parameter that is not set will return <code>gs_error_undefined (-21)</code>. Note that calling <code>gsapi_set_param</code> followed by <code>gsapi_get_param</code> may not find the value, if the device did not recognise the key as being one of its configuration keys.
</blockquote>
<h3><a name="enumerate_params"></a><code>gsapi_enumerate_params()</code></h3>
<blockquote>
Enumerate the current parameters.
Call repeatedly to list out the current parameters.
<p>
The first call should have <code>*iter = NULL</code>. Subsequent calls should pass the same pointer in so the iterator can be updated. Negative return codes indicate error, 0 success, and 1 indicates that there are no more keys to read. On success, <code>key</code> will be updated to point to a null terminated string with the key name that is guaranteed to be valid until the next call to <code>gsapi_enumerate_params</code>. If <code>type</code> is non <code>NULL</code> then <code>*type</code> will be updated to have the type of the parameter.
<p>
Note that only one enumeration can happen at a time. Starting a second enumeration will reset the first.
<p>
The enumeration only returns parameters/values that have made it to the device. Thus, any values set using the <code>gs_spt_more_to_come</code> without a following call without that flag will not be retrieved. Similarly, attempting to enumerate parameters before <code>gsapi_init_with_args</code> has been called will not list any, even if <code>gsapi_set_param</code> has been used.
</blockquote>
<h3><a name="add_control_path"></a><code>gsapi_add_control_path()</code></h3>
<blockquote>
Add a (case sensitive) path to one of the lists of permitted paths for file access.
See <a href="Use.htm#Safer">here</a> for more information about permitted paths.
</blockquote>
<h3><a name="remove_control_path"></a><code>gsapi_remove_control_path()</code></h3>
<blockquote>
Remove a (case sensitive) path from one of the lists of permitted paths for file access.
See <a href="Use.htm#Safer">here</a> for more information about permitted paths.
</blockquote>
<h3><a name="purge_control_paths"></a><code>gsapi_purge_control_paths()</code></h3>
<blockquote>
Clear all the paths from one of the lists of permitted paths for file access.
See <a href="Use.htm#Safer">here</a> for more information about permitted paths.
</blockquote>
<h3><a name="activate_path_control"></a><code>gsapi_activate_path_control()</code></h3>
<blockquote>
Enable/Disable path control (i.e. whether paths are checked against permitted paths
before access is granted).
See <a href="Use.htm#Safer">here</a> for more information about permitted paths.
</blockquote>
<h3><a name="is_path_control_active"></a><code>gsapi_is_path_control_active()</code></h3>
<blockquote>
Query whether path control is activated or not.
See <a href="Use.htm#Safer">here</a> for more information about permitted paths.
</blockquote>
<h3><a name="add_fs"></a><code>gsapi_add_fs()</code></h3>
<blockquote>
Adds a new 'Filing System' to the interpreter.
This enables callers to implement their own filing systems. The system
starts with just the conventional 'file' handlers installed, to allow
access to the local filing system. Whenever files are to be opened
from the interpreter, the file paths are offered around each registered
filing system in turn (from most recently registered to oldest), until
either an error is given, or the file is opened successfully.
<p>
Details of the <code>gsapi_fs_t</code> are given
<a href="#gsapi_fs_t">below</a>.
</blockquote>
<h3><a name="remove_fs"></a><code>gsapi_remove_fs()</code></h3>
<blockquote>
Remove a previously registered 'Filing System' from the interpreter.
Both the function pointers within the <code>gs_fs_t</code> and the
secret value must match exactly.
<p>
</blockquote>
<h3><a name="return_codes"></a>Return codes</h3>
<p>
The <code>gsapi_init_with_args</code>, <code>gsapi_run_*</code> and
<code>gsapi_exit</code> functions return an integer code.</p>
<table>
<tr>
<th colspan="3">Return Codes from gsapi_*()</th>
</tr>
<tr>
<th>CODE</th>
<th colspan="2">STATUS</th>
</tr>
<tr>
<td>0</td>
<td colspan="2">No errors</td>
</tr>
<tr>
<td>gs_error_Quit</td>
<td colspan="2">"<code>quit</code>" has been executed. This is not an error. <code>gsapi_exit()</code> must be called next.</td>
</tr>
<tr>
<td>gs_error_interrupt</td>
<td colspan="2"><a href="#set_poll">The polling callback function</a> returned a negative value, requesting Ghostscript to abort.</td>
</tr>
<tr>
<td>gs_error_NeedInput</td>
<td colspan="2">More input is needed by <code>gsapi_run_string_continue()</code>. This is not an error.</td>
</tr>
<tr>
<td>gs_error_Info</td>
<td colspan="2">"<code>gs -h</code>" has been executed. This is not an error. <code>gsapi_exit()</code> must be called next.</td>
</tr>
<tr>
<td>< 0</td>
<td colspan="2">Error</td>
</tr>
<tr>
<td><= gs_error_Fatal</td>
<td colspan="2">Fatal error. <code>gsapi_exit()</code> must be called next.</td>
</tr>
</table>
<p>
The <code>gsapi_run_*()</code> 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>
<p>
When executing a string with <code>gsapi_run_string_*()</code>,
<code>currentfile</code> is the input from the string.
Reading from <code>%stdin</code> uses the stdin callback.</p>
<h3><a name="gsapi_fs_t"></a>gsapi_fs_t</h3>
<p>Each 'filing system' within gs is a structure of function
pointers; each function pointer gives a handler from taking a
different named resource (a file, a pipe, a printer, a scratch
file etc) and attempts to open it.
<pre>
typedef struct
{
int (*open_file)(const gs_memory_t *mem,
void *secret,
const char *fname,
const char *mode,
gp_file **file);
int (*open_pipe)(const gs_memory_t *mem,
void *secret,
const char *fname,
char *rfname, /* 4096 bytes */
const char *mode,
gp_file **file);
int (*open_scratch)(const gs_memory_t *mem,
void *secret,
const char *prefix,
char *rfname, /* 4096 bytes */
const char *mode,
int rm,
gp_file **file);
int (*open_printer)(const gs_memory_t *mem,
void *secret,
char *fname, /* 4096 bytes */
int binary,
gp_file **file);
int (*open_handle)(const gs_memory_t *mem,
void *secret,
char *fname, /* 4096 bytes */
const char *mode,
gp_file **file);
} gsapi_fs_t;
</pre>
<p>If the filename (always given in utf-8 format) is recognised as
being one that the filing system handles (perhaps by the prefix used),
then it should open the file, fill in the <code>gp_file</code>
pointer and return 0.
<p>If the filename is not-recognised as being one that the filing
system handles, then returning 0 will cause the filename to be
offered to other registered filing systems.
<p>If an error is returned (perhaps gs_error_invalidfileaccess),
then no other filing system will be allowed to try to open the
file. This provides a mechanism whereby a caller to gsapi can
completely control access to all files accessed via <code>gp_fopen</code>
at runtime.
<p>Note, that while most file access within ghostscript will be
redirected via these functions, stdio will not; see the existing
mechanisms within Ghostscript for intercepting/replacing this.
<ul>
<li>The <code>open_file</code> function pointer will be called when
something (most often a call to <code>gp_fopen</code>) attempts to
open a file.
<li>The <code>open_pipe</code> function pointer will be called when
something (most often a call to <code>gp_popen</code>) attempts to
open a pipe. <code>rfname</code> points to a 4K buffer in which the
actual name of the opened pipe should be returned.
<li>The <code>open_scratch</code> function pointer will be called when
something (most often a call to <code>gp_open_scratch_file</code> or
<code>gp_open_scratch_file_rm</code>) attempts to open a temporary file.
<code>rfname</code> points to a 4K buffer in which the actual name of
the opened pipe should be returned. If <code>rm</code> is true, then
the file should be set to delete itself when all handles to it are closed.
<li>The <code>open_printer</code> function pointer will be called when
something (most often a call to <code>gp_open_printer</code>) attempts
to open a stream to a printer. If <code>binary</code> is true, then
the stream should be opened as binary; most streams will be binary by
default - this has historical meaning on OS/2.
<li>The <code>open_handle</code> function pointer will be called when
something (most often a call via the postscript <code>%handle%</code>
IO device) attempts to open a Windows handle. This entry point will
never be called on non-Windows builds.
</ul>
<p>Any of these which are left as NULL will never be called; a filing
system with all of the entries left as NULL is therefore pointless.
<p>The most complex part of the implementation of these functions
is the creation of a <code>gp_file</code> instance to return. There are
some helper functions for this, best explained by example.
<p>Let us consider a hypothetical filing system that encrypts data as
it is written, and decrypts it as it is read back. As each file is
read and written the encryption/decryption routines will need to use
some state, carried between calls to the filing system. We therefore
might define a new type 'derived' from <code>gp_file</code> as follows:
<pre>
typedef struct
{
gp_file base;
/* State private to the implementation of this file for encryption/decryption */
/* For example: */
int foo;
char *bar;
} gp_file_crypt;
</pre>
<p>An implementation of <code>gs_fs_t</code> for our 'crypt' filing system
might then look like this:
<pre>
gsapi_fs_t gs_fs_crypt =
{
crypt_open_file,
NULL, /* open_pipe */
NULL, /* open_scratch */
NULL, /* open_printer */
NULL /* open_handle */
};
</pre>
<p>In the above definition, we define a single handler, to cope with the
opening of our input/output files. If we wanted to encrypt/decrypt
other files too (perhaps the temporary files we produce) we'd need to
define additional handlers (such as <code>open_scratch</code>).
<p>Our handler might look as follows:
<pre>
int crypt_open_file(const gs_memory_t *mem,
void *secret,
const char *filename,
const char *mode,
gp_file **file)
{
gp_file_crypt crypt;
/* Ignore any filename not starting with "crypt://" */
if (strncmp(filename, "crypt://", 8) != 0)
return 0;
/* Allocate us an instance (and fill in the non-crypt-specific
* internals) */
crypt = (gp_file_crypt *)gp_file_alloc(mem, &crypt_ops, sizeof(*crypt), "gp_file_crypt");
if (crypt == NULL)
return gs_error_VMerror; /* Allocation failed */
/* Setup the crypt-specific state */
crypt->foo = 1;
crypt->bar = gs_alloc_bytes(mem->non_gc_memory, 256, "bar");
/* If allocations fail, we need to clean up before exiting */
if (crypt->bar) {
gp_file_dealloc(crypt);
return gs_error_VMerror;
}
/* Return the new instance */
*file = &crypt.base;
return 0;
}
</pre>
<p>The crucial part of this function is the definition of <code>crypt_ops</code>,
an instance of the <code>gp_file_ops_t</code> type; a table of function pointers
that implement the actual operations required.
<pre>
typedef struct {
int (*close)(gp_file *);
int (*getc)(gp_file *);
int (*putc)(gp_file *, int);
int (*read)(gp_file *, size_t size, unsigned int count, void *buf);
int (*write)(gp_file *, size_t size, unsigned int count, const void *buf);
int (*seek)(gp_file *, gs_offset_t offset, int whence);
gs_offset_t (*tell)(gp_file *);
int (*eof)(gp_file *);
gp_file *(*dup)(gp_file *, const char *mode);
int (*seekable)(gp_file *);
int (*pread)(gp_file *, size_t count, gs_offset_t offset, void *buf);
int (*pwrite)(gp_file *, size_t count, gs_offset_t offset, const void *buf);
int (*is_char_buffered)(gp_file *file);
void (*fflush)(gp_file *file);
int (*ferror)(gp_file *file);
FILE *(*get_file)(gp_file *file);
void (*clearerr)(gp_file *file);
gp_file *(*reopen)(gp_file *f, const char *fname, const char *mode);
} gp_file_ops_t;
</pre>
<p>These functions generally follow the same patterns as the posix functions that match them,
and so in many cases we will describe these with references to such.
Whenever these routines are called, they will be passed a <code>gp_file</code> pointer.
This pointer will have originated from the <code>crypt_open_file</code> call, and so can
safely be cast back to a <code>gp_file_crypt</code> pointer to allow private data to be accessed.
<dl>
<dt><code>close(gp_file *)</code>
<dd>close the given file; free any storage in the crypt specific parts of <code>gp_file_crypt</code>,
but not the gp_file_crypt structure itself.
<dt><code>int getc(gp_file *)</code>
<dd>Get a single character from the file, returning it as an int (or -1 for EOF).
Behaves like <code>fgetc(FILE *)</code>.
<dt><code>int putc(gp_file *, int)</code>
<dd>Put a single character to the file, returning the character on success, or
EOF (and setting the error indicator) on error.
Behaves like <code>fgetc(FILE *)</code>.
<dt><code>int read(gp_file *, size_t size, unsigned int count, void *buf)</code>
<dd>Reads count entries of size bytes the file into buf, returning the number
of entries read. Behaves like <code>fread(FILE *, size, count, buf)</code>.
<dt><code>int write(gp_file *, size_t size, unsigned int count, const void *buf)</code>
<dd>Writes count entries of size bytes from buf into the file, returning the
number of entries written. Behaves like <code>fwrite(FILE *, size, count, buf)</code>.
<dt><code>int seek(gp_file *, gs_offset_t offset, int whence)</code>
<dd>Seeks within the file. Behaves like <code>fseek(FILE *, offset, whence)</code>.
<dt><code>gs_offset_t tell(gp_file *)</code>
<dd>Returns the current offset within the file. Behaves like <code>ftell(FILE *)</code>.
<dt><code>int eof(gp_file *)</code>
<dd>Returns 1 if we are at the end of the file, 0 otherwise. Behaves like
<code>feof(FILE *)</code>.
<dt><code>gp_file * dup(gp_file *, const char *mode)</code>
<dd>Optional function, only used if clist files are to be stored in this filing system.
Behaves like <code>fdup(FILE *)</code>. Leave NULL if not implemented.
<dt><code>int seekable(gp_file *)</code>
<dd>Returns 1 if the file is seekable, 0 otherwise. Certain output devices will
only work with seekable files.
<dt><code>int pread(gp_file *, size_t count, gs_offset_t offset, void *buf)</code>
<dd>Optional function, only used if clist files are to be stored in this filing system.
Behaves like an atomic <code>fseek(FILE *, offset, 0)</code> and <code>fread(FILE *, 1, count, buf)</code>.
Akin to <code>pread</code>.
<dt><code>int pwrite(gp_file *, size_t count, gs_offset_t offset, const void *buf)</code>
<dd>Optional function, only used if clist files are to be stored in this filing system.
Behaves like an atomic <code>fseek(FILE *, offset, 0)</code> and <code>fwrite(FILE *, 1, count, buf)</code>.
Akin to <code>pwrite</code>.
<dt><code>int is_char_buffered(gp_file *file)</code>
<dd>Returns 1 if the file is character buffered, 0 otherwise. Used for handling
reading from terminals. Very unlikely to be used, so returning 0 all the time
should be safe. Leave NULL to indicate "always 0".
<dt><code>void fflush(gp_file *file)</code>
<dd>Ensures that any buffered data is written to the file. Behaves like <code>fflush(FILE *)</code>.
Leave NULL to indicate that no flushing is ever required.
<dt><code>int ferror(gp_file *file)</code>
<dd>Returns non-zero if there has been an error, or 0 otherwise. Behaves like <code>ferror(FILE *)</code>.
<dt><code>FILE * get_file(gp_file *file)</code>
<dd>Optional: Gets the FILE * pointer that backs this file. Required for a few devices
that insist on working with FILE *'s direct. Generally safe to leave this set to NULL, and those
devices will fail gracefully.
<dt><code>void clearerr(gp_file *file)</code>
<dd>Clear the error and EOF values for a file. Behaves like <code>clearerror(FILE *)</code>.
<dt><code>gp_file * reopen(gp_file *f, const char *fname, const char *mode)</code>
<dd>Optional function, only used if the <code>gp_file</code> came from an <code>open_scratch</code>
call; can be left as NULL if the <code>open_scratch</code> pointer is set to NULL.
Reopen a stream with a different mode. Behaves like
<code>freopen(fname, mode, FILE *)</code>.
</dl>
<h3><a name="callout"></a>Callouts</h3>
<blockquote>
<p>Callouts are a mechanism
for the core code (specifically devices) to communicate with the
user of gsapi. This communication can take the form of passing
information out vis-a-vis what devices are doing, or requesting
configuration from the caller to affect exactly how the device
itself works.</p>
<p>This is deliberately an extensible system, so exact details of
callouts should be documented with the device in question. In general
however a callout handler will be of the form:</p>
<pre>
typedef int (*gs_callout)(void *callout_handle,
const char *device_name,
int id,
int size,
void *data);
</pre>
<p>The <code>callout_handle</code> value passed to the callout will
be the value passed in at registration. The <code>device_name</code>
should be a null-terminated string giving the name of the device
(though care should be taken to cope with the case where
<code>device_name</code> is NULL for potential future uses).
The <code>id</code> value will have a (device-specific) meaning; see
the documentation for the device in question for more details. The
same <code>id</code> value may be used to mean different things in
different devices.
Finally, <code>size</code> and <code>data</code> have callout
specific meanings, but typically, <code>data</code> will be a pointer
to data block (which may either be uninitialised or wholly/partially
initialised on entry, and may be updated on exit), and <code>size</code>
will be the size (in bytes) of the block pointed to by <code>data</code>.
</p>
<p>A return value of -1 (<code>gs_error_unknownerror</code>) means
the callout was not recognised by the handler, and should be passed
to more handlers. Other negative values are interpreted as standard
Ghostscript error values, and stop the propagation of the callout.
Non-negative return codes mean the callout was handled and should
not be passed to any more registered callout handlers.</p>
</blockquote>
<hr>
<h2><a name="Example_usage"></a>Example Usage</h2>
<p>To try out the following 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><a name="Example_1"></a>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 = NULL;
int main(int argc, char *argv[])
{
int code, code1;
const char * gsargv[7];
int gsargc;
gsargv[0] = "";
gsargv[1] = "-dNOPAUSE";
gsargv[2] = "-dBATCH";
gsargv[3] = "-dSAFER";
gsargv[4] = "-sDEVICE=pdfwrite";
gsargv[5] = "-sOutputFile=out.pdf";
gsargv[6] = "input.ps";
gsargc=7;
code = gsapi_new_instance(&minst, NULL);
if (code < 0)
return 1;
code = gsapi_set_arg_encoding(minst, GS_ARG_ENCODING_UTF8);
if (code == 0)
code = gsapi_init_with_args(minst, gsargc, gsargv);
code1 = gsapi_exit(minst);
if ((code == 0) || (code == gs_error_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == gs_error_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 = NULL;
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_set_arg_encoding(minst, GS_ARG_ENCODING_UTF8);
if (code == 0)
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 == gs_error_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == gs_error_Quit))
return 0;
return 1;
}
</pre>
<h3>Example 3</h3>
<p>Replace main() in either of the above with the following code,
showing how you can feed Ghostscript piecemeal:</p>
<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_set_arg_encoding(minst, GS_ARG_ENCODING_UTF8);
if (code == 0)
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 == gs_error_Quit))
code = code1;
gsapi_delete_instance(minst);
if ((code == 0) || (code == gs_error_Quit))
return 0;
return 1;
}
</pre>
<h3>Example 4</h3>
<p>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:</p>
<pre>
code = gsapi_run_string(minst, "(example.pdf) .runlibfile", 0, &exit_code);
</pre>
<p>and Ghostscript would open and process the file named "example.pdf" as
if it had been passed as an argument to
<code>gsapi_init_with_args()</code>.</p>
<hr>
<h2><a name="Multiple_threads"></a>Multiple threads</h2>
<p>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 "><code>gsapi_*()</code></a>
functions must be called from one thread only.</p>
<hr>
<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.</p>
<ul>
<li>If you do nothing, the "C" stdio will be used.</li>
<li>If you use <code>gsapi_set_stdio()</code>, 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.</li>
</ul>
<p>
The callback functions are described in
<a href="../psi/iapi.h"><code>iapi.h</code></a>.</p>
<hr>
<h2><a name="display"></a>Display device</h2>
<p>
The <code>display</code> device is available for use with
the Ghostscript interpreter library. While originally designed
for allowing screen display of rendered output from Ghostscript,
this is now powerful enough to provide a simple mechanism for
getting rendered output suitable for use in all manner of
output scenarios, including printing.</p>
<p>Details of the API and options are given in the file
<code><a href="../devices/gdevdsp.h">gdevdsp.h</a></code>.
This device provides you with access to the raster output of
Ghostscript. It is the callers responsibility to copy this raster
to a display window or printer.</p>
<p>
In order for this device to operate, it needs access to a structure
containing a set of callback functions, and a callback handle (an
opaque <code>void *</code> that can be used by caller to locate its
own state). There are 2 ways that the device can get this
information, a legacy method, and a modern method.
</p>
<dl>
<dt>Legacy method</dt>
<dd>
<p>The address of the callback structure, is provided
using <code>gsapi_set_display_callback()</code>.
This must be called after
<code>gsapi_new_instance()</code>
and before
<code>gsapi_init_with_args()</code>.</p>
<p>
With this call, the callback handle is passed as NULL by default, but can
be overridden by using a parameter. We actively dislike
this way of working, as we consider passing addresses
via the command line distasteful. The handle can be
set using</p>
<blockquote>
-sDisplayHandle=1234
</blockquote>
<p>
Where "1234" is a string. The API was changed to use a string
rather than an integer/long value when support for 64 bit systems
arrived. A display "handle" is often a pointer, and since these
command line options have to survive being processed by Postscript
machinery, and Postscript only permits 32 bit number values, a
different representation was required. Hence changing the value
to a string, so that 64 bit values can be supported. The string
formats allowed are:</p>
<blockquote>
<code>1234</code> - implicit base 10
</blockquote>
<blockquote>
<code>10#1234</code> - explicit base 10
</blockquote>
<blockquote>
<code>16#04d2</code> - explicit base 16
</blockquote>
<p>
The "number string" is parsed by the display device to retrieve
the number value, and is then assigned to the void pointer
parameter "pHandle" in the display device structure. Thus, for
a trivial example, passing <code>-sDisplayHandle=0</code> will result
in the first parameter passed to your display device callbacks being:
<code>(void *)0</code>.</p>
<p>
The previous API, using a number value:</p>
<blockquote>
-dDisplayHandle=1234
</blockquote>
<p>
is still supported on 32 bit systems, but will cause a "typecheck"
error on 64 bit systems, and is considered deprecated. It should
not be used in new code.</p>
</dd>
<dt>Modern method
<dd>
<p>The preferred method is to register a callout handler using
<code><a href="#register_callout">gsapi_register_callout</a></code>.
When this handler is called for the <code>"display"</code>
device, with <code>id = 0</code> (= <code>DISPLAY_CALLOUT_GET_CALLBACK</code>),
then <code>data</code> should point to an empty <code>gs_display_get_callback_t</code>
block, with <code>size = sizeof(gs_display_get_callback_t)</code>.
</p>
<pre>
typedef struct {
display_callback *callback;
void *caller_handle;
} gs_display_get_callback_t;
</pre>
<p>The handler should fill in the structure before returning,
with a return code of 0.</p>
</dd>
</dl>
<p>
Note, that the <code>DisplayHandle</code> value is only consulted for
display device callbacks registered using the (legacy, now deprecated)
<code>gsapi_set_display_callback</code> API, not the preferred
<code>gsapi_register_callout</code> based mechanism.
<p>
The device raster format can be configured using</p>
<blockquote>
-dDisplayFormat=NNNN
</blockquote>
<p>Options include</p>
<ul>
<li> native, gray, RGB, CMYK or separation color spaces.</li>
<li> alpha byte (ignored).</li>
<li> 1 to 16 bits/component.</li>
<li> bigendian (RGB) or littleendian (BGR) order.</li>
<li> top first or bottom first raster.</li>
<li> 16 bits/pixel with 555 or 565 bitfields.</li>
<li> Chunky, Planar and Planar interleaved formats.</li>
<li> "Full screen" or "Rectangle Request" modes of operation.</li>
</ul>
<p>The operation of the device is best described with a walkthrough
of some example code that uses it. For simplicity and clarity, we
have omitted the error handling code in this example; in production
code, every place where we get a <code>code</code> value returned
we should check it for failure (a negative value) and clean up
accordingly. First, we create an instance of Ghostscript:</p>
<pre>
void *minst = NULL;
code = gsapi_new_instance(&minst, NULL);
code = gsapi_set_stdio(minst, gsdll_stdin, gsdll_stdout, gsdll_stderr);
</pre>
<p>Next, we have to give the display device the address of our
callback structure. In old code, we would do so using something
like this:</p>
<pre>
code = gsapi_set_display_callback(minst, &display_callback);
</pre>
<p>We strongly recommend that you don't do that, but instead use the
more modern <a href="callout">callout</a> mechanism:</p>
<pre>
code = gsapi_register_callout(minst, my_callout_handler, state);
</pre>
<p>where <code>state</code> is any <code>void *</code> value you like,
usually a pointer to help you reach any internal state you may need.
Earlier in your code you would have the definition of
<code>my_callout_handler</code> that might look like this:</p>
<pre>
static int
my_callout_handler(void *instance,
void *callout_handle,
const char *device_name,
int id,
int size,
void *data)
{
/* On entry, callout_handle == the value of state passed in
* to gsapi_register_callout. */
/* We are only interested in callouts from the display device. */
if (device_name == NULL || strcmp(device_name, "display"))
return -1;
if (id == DISPLAY_CALLOUT_GET_CALLBACK)
{
/* Fill in the supplied block with the details of our callback
* handler, and the handle to use. In this instance, the handle
* is the pointer to our test structure. */
gs_display_get_callback_t *cb = (gs_display_get_callback_t *)data;
cb->callback = &display_callback;
cb->caller_handle = callout_handle;
return 0;
}
return -1;
}
</pre>
<p>As you can see, this callout handler only responds to callouts
for the display device, and then only for one particular function
(<code>id</code>). It returns the same <code>display_callback</code>
structure as the deprecated, legacy mechanism passed in using
<code>gsapi_set_display_callback</code>, with the added benefit that
the <code>caller_handle</code> value can be passed in too. In this
example we pass in the same value as was used for <code>callout_handle</code>,
but implementations are free to use any value they want.</p>
<p>Returning to our example, we now set up a set of arguments to
setup Ghostscript:</p>
<pre>
int argc = 0;
/* Allow for up to 32 args of up to 64 chars each. */
char argv[32][64];
sprintf(argc[argc++], "gs");
sprintf(argv[argc++], "-sDEVICE=display");
</pre>
<p>The zeroth arg is a dummy argument to match the standard C mechanism
for passing arguments to a program. Traditionally this is the name of
the program being invoked. Next, we tell Ghostscript to use the display
device.</p>
<pre>
sprintf(argv[argc++], "-sDEVICE=display");
</pre>
Next we tell the display device what output format to use. The
format is flexible enough to support common Windows, OS/2, Linux
and Mac raster formats. <p>The format values are described in
<code><a href="../devices/gdevdsp.h">gdevdsp.h</a></code>.
To select the display device with a Windows 24-bit RGB raster:</p>
<pre>
sprintf(argv[argc++], "-dDisplayFormat=%d",
DISPLAY_COLORS_RGB | DISPLAY_ALPHA_NONE | DISPLAY_DEPTH_8 |
DISPLAY_LITTLEENDIAN | DISPLAY_BOTTOMFIRST);
</pre>
<p>If (and only if) you used the legacy mechanism described above, you
will need another argument to pass in the <code>caller_handle</code>
value to be parroted back to the functions listed within
<code>display_callback</code>:</p>
<pre>
sprintf(arg2, "-dDisplayHandle=%d", callout_handle);
</pre>
<p>Any other arguments that you want can be added to the end of
the command line, typically including a file to run. Then we pass
that all to Ghostscript:
<pre>
code = gsapi_init_with_args(minst, argc, argv);
</pre>
<p><a name="display_callback"></a>At this point you should start to
see your display callback functions being called. Exactly which callback
functions are provided, and how they respond will determine exactly
how the display device operates. The primary choice will be whether the
device runs in "full page" or "rectangle request"
mode. Details of these are given below.</p>
<p>Once we have finished processing the file, we can process
other files using <code>gsapi_run_file</code>, or feed in data
using <code>gsapi_run_string</code>. Once you have finished, you
can shut the interpreter down and exit, using:</p>
<pre>
code = gsapi_exit(minst);
gsapi_delete_instance(minst);
</pre>
<p>A full list of the display callback functions can be found in
<code><a href="../devices/gdevdsp.h">gdevdsp.h</a></code>. There
are several different versions of the callback, corresponding to
different "generations" of the device. In general
you should use the latest one. The <code>size</code> field of
the structure should be initialised to the size of the structure
in bytes.</p>
<h3><a name="display_open"></a>display_open</h3>
<pre>int (*display_open)(void *handle, void *device);</pre>
<p>This function will be called when the display device is
opened. The device may be opened and closed many times,
sometimes without any output being produced.</p>
<h3><a name="display_preclose"></a>display_preclose</h3>
<pre>int (*display_preclose)(void *handle, void *device);</pre>
<p>This function will be called when the display device is
about to be closed. The device will not actually be closed
until this function returns.</p>
<h3><a name="display_close"></a>display_close</h3>
<pre>int (*display_close)(void *handle, void *device);</pre>
<p>This function will be called once the display device has
been closed. There will be no more events from the device
unless/until it is reopened.</p>
<h3><a name="display_presize"></a>display_presize</h3>
<pre>int (*display_presize)(void *handle, void *device,
int width, int height, int raster, unsigned int format);</pre>
<p>This function will be called when the display device is
about to be resized. The device will only be resized if this
function returns 0.</p>
<h3><a name="display_size"></a>display_size</h3>
<pre>int (*display_size)(void *handle, void *device, int width, int height,
int raster, unsigned int format, unsigned char *pimage);</pre>
<p>This function will be called when the display device is
has been resized. The pointer to the raster image is pimage.</p>
<h3><a name="display_sync"></a>display_sync</h3>
<pre>int (*display_sync)(void *handle, void *device);</pre>
<p>This function may be called periodically during display
to flush the page to the display.</p>
<h3><a name="display_page"></a>display_page</h3>
<pre>int (*display_page)(void *handle, void *device, int copies, int flush);</pre>
<p>This function is called on a "showpage" operation
(i.e. at the end of every page). Operation will continue as soon as
this function returns.</p>
<h3><a name="display_update"></a>display_update</h3>
<pre>int (*display_update)(void *handle, void *device,
int x, int y, int w, int h);</pre>
<p>This function <strong>may</strong> get called repeatedly
during rendering to indicate that an area of the output has
been updated. Certain types of rendering will not see this
function called back at all (in particular files using
transparency).</p>
<h3><a name="display_memalloc"></a>display_memalloc</h3>
<pre>int (*display_memalloc)(void *handle, void *device,
size_t long size);</pre>
<p><strong>Note:</strong> In older versions of this API,
size is an <code>unsigned long</code> rather than a
<code>size_t</code>.</p>
<p>If this function pointer is sent as NULL, then the
display device will handle all the memory allocations
internally, and will always work in full page rendering
mode.</p>
<p>Otherwise, this function will be called to allocate
the storage for the page to be rendered into. If a non-NULL
value is returned, then the device will proceed to render
the full page into it. If NULL is returned, then the device
will check a) whether we are using a V2 or greater display
callback structure and b) whether that structure specifies
a <code>rectangle_request</code> function pointer.</p>
<p>If both of those conditions are true, then the device
will continue in rectangle request mode. Otherwise it will
fail with an out of memory error.</p>
<h3><a name="display_memfree"></a>display_memfree</h3>
<pre>int (*display_memfree)(void *handle, void *device, void *ptr);</pre>
<p>This function should be NULL if and only if
<code><a href="#display_memalloc">display_memalloc</a></code> is
NULL. Any memory allocated using <code>display_memalloc</code> will be
freed via this function.</p>
<h3><a name="display_separation"></a>display_separation</h3>
<pre>int (*display_separation)(void *handle, void *device,
int component, const char *component_name,
unsigned short c, unsigned short m,
unsigned short y, unsigned short k);</pre>
<p>When using <code>DISPLAY_COLORS_SEPARATION</code>, this function
will be called once for every separation component - first
"Cyan", "Magenta", "Yellow" and
"Black", then any spot colors used. The supplied
<code>c</code>, <code>m</code>, <code>y</code> and <code>k</code>
values give the equivalent color for each spot. Each colorant
value ranges from 0 (for none) to 65535 (full).</p>
<p>In separation color mode you are expected to count the number
of calls you get to this function after each
<code><a href="#display_size">display_size</a></code> to know how many
colors you are dealing with.</p>
<h3><a name="display_adjust_band_height"></a>display_adjust_band_height</h3>
<pre>int (*display_adjust_band_height)(void *handle, void *device,
int bandheight);</pre>
<p>When running in "rectangle request mode" the device
first renders the page to a display list internally. It can then
be played back repeatedly so that different regions (rectangles)
of the page can be extracted in sequence. A common use of this is
to support "banded" operation, where the page is divided
into multiple non-overlapping bands of a fixed height.</p>
<p>The display device itself will pick an appropriate band height
for it to use. If this function pointer is left as NULL then this
value will be used unchanged. Otherwise, the proposed value will
be offered to this function. This function can override the choice
of bandheight, by returning the value that it would like to be
used in preference.</p>
<p>In general, this figure should (as much as possible) only be
adjusted downwards. For example, a device targeting an inkjet printer
with 200 nozzles in the print head might like to extract bands
that are a multiple of 200 lines high. So the function might
return <code>max(200, 200*(bandheight/200))</code>. If the function
returns 0, then the existing value will be used unchanged.</p>
<p>Any size rectangle can be chosen with any size bandheight,
so ultimately the value chosen here will not matter much. It
may make some small difference in speed in some cases.</p>
<h3><a name="display_rectangle_request"></a>display_rectangle_request</h3>
<pre>int (*display_rectangle_request)(void *handle, void *device,
void **memory, int *ox, int *oy,
int *raster, int *plane_raster,
int *x, int *y, int *w, int *h);</pre>
<p>If the display device chooses to use rectangle request mode,
this function will be called repeatedly to request a rectangle
to render. Ghostscript will render the rectangle, and call this
function again. The implementer is expected to handle the rectangle
that has just been rendered, and to return the details of another
rectangle to render. This will continue until a rectangle with
zero height or width is returned, whereupon Ghostscript will
continue operation.</p>
<p>On entry, <code>*raster</code> and <code>*plane_raster</code>
are set to the values expected by the format in use. All the
other pointers point to uninitialised values.</p>
<p>On exit, the values should be updated appropriately. The
implementor is expected to store the values returned so that
the rendered output given can be correctly interpreted when
control returns to this function.</p>
<p><code>memory</code> should be updated to point to a block of
memory to use for the rendered output. Pixel (<code>*ox</code>,
<code>*oy</code>) is the first pixel represented in that block.
<code>*raster</code> is the number of bytes difference between
the address of component 0 of Pixel(<code>*ox</code>, <code>*oy</code>)
and the address of component 0 of Pixel(<code>*ox</code>,
<code>1+*oy</code>). <code>*plane_raster</code> is the number of
bytes difference between the address of component 0 of
Pixel(<code>*ox</code>, <code>*oy</code>) and the address of
component 1 of Pixel(<code>*ox</code>, <code>*oy</code>), if in
planar mode, 0 otherwise. <code>*x</code>, <code>*y</code>,
<code>*w</code> and <code>*h</code> give the rectangle requested
within that memory block.</p>
<p>Any set of rectangles can be rendered with this method, so this
can be used to drive Ghostscript in various ways. Firstly, it is
simple to request a set of non-overlapping "bands" that
cover the page, to drive a printer. Alternatively, rectangles can
be chosen to fill a given block of memory to implement a window
panning around a larger page. Either the whole image could be
redrawn each time, or smaller rectangles around the edge of the
panned area could be requested. The choice is down to the caller.</p>
<p>
Some examples of driving this code in full page mode are in
<code><a href="../psi/dwmain.c">dwmain.c</a></code> (Windows),
<code><a href="../psi/dpmain.c">dpmain.c</a></code> (OS/2) and
<code><a href="../psi/dxmain.c">dxmain.c</a></code> (X11/Linux), and
<code><a href="../psi/dmmain.c">dmmain.c</a></code> (MacOS Classic or Carbon).</p>
<p>Alternatively an example that drives this code in both full page
and rectangle request mode can be found in
<code><a href="../demos/c/api_test.c">api_test.c</a></code>.</p>
<p>
On some platforms, the calling convention for the display device callbacks in
<code><a href="../devices/gdevdsp.h">gdevdsp.h</a></code>
is not the same as the exported
<a href="#Exported_functions "><code>gsapi_*()</code></a>
functions in <a href="../psi/iapi.h"><code>iapi.h</code></a>.</p></p>
<!-- [2.0 end contents] ==================================================== -->
<!-- [3.0 begin visible trailer] =========================================== -->
<hr>
<p>
<small>Copyright © 2000-2021 Artifex Software, Inc. All rights reserved.</small></p>
<p>
This software is provided AS-IS with no warranty, either express or
implied.</p>
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 <a href="https://www.artifex.com">https://www.artifex.com</a>
or contact Artifex Software, Inc., 1305 Grant Avenue - Suite 200,
Novato, CA 94945, U.S.A., +1(415)492-9861, for further information.</p>
<p>
<small>Ghostscript version 9.55.0, 27 September 2021
<!-- [3.0 end visible trailer] ============================================= -->
<!--FINISH EDITING HERE-->
</div><!-- close inner -->
</div><!-- close outer -->
</article>
</main>
<script src="site.js"></script>
</body>
</html>
|
