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<h1>The Ghostscript Interpreter Application Programming Interface (API)</h1>

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<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"><code>gsapi_revision</code></a>
<li><a href="#new_instance"><code>gsapi_new_instance</code></a>
<li><a href="#delete_instance"><code>gsapi_delete_instance</code></a>
<li><a href="#set_stdio"><code>gsapi_set_stdio</code></a>
<li><a href="#set_poll"><code>gsapi_set_poll</code></a>
<li><a href="#set_display_callback"><code>gsapi_set_display_callback</code></a>
<li><a href="#set_arg_encoding"><code>gsapi_set_arg_encoding</code></a>
<li><a href="#run"><code>gsapi_run_string_begin</code></a>
<li><a href="#run"><code>gsapi_run_string_continue</code></a>
<li><a href="#run"><code>gsapi_run_string_end</code></a>
<li><a href="#run"><code>gsapi_run_string_with_length</code></a>
<li><a href="#run"><code>gsapi_run_string</code></a>
<li><a href="#init"><code>gsapi_init_with_args</code></a>
<li><a href="#run"><code>gsapi_run_*</code></a>
<li><a href="#exit"><code>gsapi_exit</code></a>
<li><a href="#set_visual_tracer"><code>gsapi_set_visual_tracer</code></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>

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<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.

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<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 <code>gsdll32.dll</code>
can be used by multiple programs simultaneously, but only once 
within each process.

<li>The OS/2 DLL <code>gsdll2.dll</code> has
MULTIPLE NONSHARED data segments and can be called by multiple programs
simultaneously.

<li>The Linux shared object <code>libgs.so</code>
can be used by multiple programs simultaneously.

<li>The MacOS X <code>Ghostscript.framework</code> can also be used
by multiple applications at once.
</ul>

<p>
The source for the executable is in <code>dw</code>*.* (Windows),
<code>dp</code>*.* (OS/2) and  <code>dx</code>*.* (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 <code>dm</code>*.*.

<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 &lt;Ghostscript/ierrors.h&gt;
#include &lt;Ghostscript/iapi.h&gt;</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="../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.


<ul>
<li><code>
int 
<a href="#revision">gsapi_revision</a>
  (gsapi_revision_t *pr, int len);
</code>

<li><code>
int 
<a href="#new_instance">gsapi_new_instance</a>
(void **pinstance, void *caller_handle);
</code>

<li><code>
void 
<a href="#delete_instance">gsapi_delete_instance</a>
(void *instance);
</code>

<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><code>
int 
<a href="#set_poll">gsapi_set_poll</a>
(void *instance, int(*poll_fn)(void *caller_handle));
</code>

<li><code>
int 
<a href="#set_display_callback">gsapi_set_display_callback</a>
(void *instance, display_callback *callback);
</code>

<li><code>
int 
<a href="#set_arg_encoding">gsapi_set_arg_encoding</a>
(void *instance, int encoding);
</code>

<li><code>
int 
<a href="#init">gsapi_init_with_args</a>
(void *instance, int argc, char **argv);
</code>

<li><code>
int 
<a href="#run">gsapi_run_string_begin</a>
(void *instance, int user_errors, int *pexit_code);
</code>

<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><code>
int 
<a href="#run">gsapi_run_string_end</a>
(void *instance, int user_errors, int *pexit_code);
</code>

<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><code>
int 
<a href="#run">gsapi_run_string</a>
(void *instance, 
    const char *str, int user_errors, int *pexit_code);
</code>

<li><code>
int 
<a href="#run">gsapi_run_file</a>
(void *instance, 
    const char *file_name, int user_errors, int *pexit_code);
</code>

<li><code>
int 
<a href="#exit">gsapi_exit</a>
(void *instance);
</code>

<li><code>
int
<a href="#set_visual_tracer">gsapi_set_visual_tracer</a>
(gstruct vd_trace_interface_s *I);
</code>

</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(&amp;r, sizeof(r)) == 0) {
    if (r.revision &lt; 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 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>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).
</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"></a><code>gsapi_set_stdio()</code></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><code>gsapi_set_poll()</code></h3>
<blockquote>
Set the callback function for polling. 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>
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.
</blockquote>

<h3><a name="set_display_callback"></a><code>gsapi_set_display_callback()</code></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 
<code>gsapi_new_instance()</code>
and before <code>gsapi_init_with_args()</code>.
See <code><a href="../base/gdevdsp.h">gdevdsp.h</a></code>
for more details.
</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="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 &lt;= -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>e_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>e_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>
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.
</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_visual_tracer"></a><code>gsapi_set_visual_tracer()</code></h3>
<blockquote>
Pass visual tracer interface block to Ghostscript.
See <a href="Lib.htm#Visual_trace"><code>Lib.htm</code></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 <code>gsapi_init_with_args</code>, <code>gsapi_run_*</code> and
<code>gsapi_exit</code> 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 <code>gsapi_*()</code></font><hr>
<tr valign=bottom>
	<th align=left>Code
	<td>&nbsp;&nbsp;&nbsp;&nbsp;
	<th align=left>Status
<tr>	<td colspan=3><hr>
<tr valign=top>	<td align=left>0
	<td>&nbsp;
	<td>No errors
<tr valign=top>	<td align=left>e_Quit
	<td>&nbsp;
	<td>"<code>quit</code>" has been executed.
	This is not an error.
	<code>gsapi_exit()</code> must be called next.
<tr valign=top>	<td align=left>e_interrupt
	<td>&nbsp;
	<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>&nbsp;
	<td>More input is needed by
        <code>gsapi_run_string_continue()</code>.
        This is not an error.
<tr valign=top>	<td align=left>e_Info
	<td>&nbsp;
	<td>"<code>gs -h</code>" has been executed. 
	This is not an error.
	<code>gsapi_exit()</code> must be called next.
<tr valign=top>	<td align=left>&lt; 0
	<td>&nbsp;
	<td>Error
<tr valign=top>	<td align=left>&lt;= -100
	<td>&nbsp;
	<td>Fatal error.
<code>gsapi_exit()</code> must be called next.
</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>
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.



<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) &amp;&amp; !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 &lt;windows.h&gt;
# 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(&amp;minst, NULL);
    if (code &lt; 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 == 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) &amp;&amp; !defined(_Windows)
# define _Windows
#endif
#ifdef _Windows
/* Compile directly with:
 *   cl -D_Windows -Isrc -Febin\gstest.exe gstest.c bin\gsdll32.lib
 */
# include &lt;windows.h&gt;
# define GSDLLEXPORT __declspec(dllimport)
#endif
#include &lt;stdio.h&gt;
#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 &lt; 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(&amp;minst, NULL);
    if (code &lt; 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, &amp;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(&amp;minst, NULL);
    if (code &lt; 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, &amp;exit_code);
	gsapi_run_string_continue(minst, command, strlen(command), 0, &amp;exit_code);
	gsapi_run_string_continue(minst, "qu", 2, 0, &amp;exit_code);
	gsapi_run_string_continue(minst, "it", 2, 0, &amp;exit_code);
	gsapi_run_string_end(minst, 0, &amp;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, &amp;exit_code);
</pre>

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>.

<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 "><code>gsapi_*()</code></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 <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.
</ul>
<p>
The callback functions are described in 
<a href="../psi/iapi.h"><code>iapi.h</code></a>.


<h2><a name="display"></a>Display device</h2>
<p>
The <code>display</code> device is available for use with
the Ghostscript interpreter library.  This is described in the file 
<code><a href="../base/gdevdsp.h">gdevdsp.h</a></code>.
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 
<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>
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>
  -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:
<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>
The previous API, using a number value:
<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>
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 
<code><a href="../base/gdevdsp.h">gdevdsp.h</a></code>.
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(&amp;minst, NULL);
    gsapi_set_stdio(minst, gsdll_stdin, gsdll_stdout, gsdll_stderr);
    code = gsapi_set_display_callback(minst, &amp;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 <code>display_size()</code> callback.
You are then responsible for displaying this raster.
Some examples 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>
On some platforms, the calling convention for the display device callbacks in 
<code><a href="../base/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>

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<p>
<small>Copyright &copy; 2000-2006 Artifex Software, Inc.  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 9.18, 5 October 2015


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