<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><title>How to use the Ghostscript Dynamic Link Library (DLL)</title><!-- $Id: DLL.htm,v 1.43 2005/10/20 19:46:23 ray Exp $ --><!-- Originally: dll.txt --><link rel="stylesheet" type="text/css" href="gs.css" title="Ghostscript Style"></head> <body><!-- [1.0 begin visible header] ============================================ --> <!-- [1.1 begin headline] ================================================== --> <h1>How to use the Ghostscript Dynamic Link Library (DLL)</h1> <!-- [1.1 end headline] ==================================================== --> <!-- [1.2 begin table of contents] ========================================= --> <h2>Table of contents</h2> <ul><li><a href="#DLL">What is the Ghostscript DLL?</a><li><a href="#Common_functions">Platform-independent DLL functions</a><ul><li><a href="#revision"><b><tt>gsdll_revision()</tt></b></a><li><a href="#init"><b><tt>gsdll_init()</tt></b></a><li><a href="#execute_begin"><b><tt>gsdll_execute_begin()</tt></b></a><li><a href="#execute_cont"><b><tt>gsdll_execute_cont()</tt></b></a><li><a href="#execute_end"><b><tt>gsdll_execute_end()</tt></b></a><li><a href="#exit"><b><tt>gsdll_exit()</tt></b></a><li><a href="#lock_device"><b><tt>gsdll_lock_device()</tt></b></a></ul><li><a href="#Callback">Callback function</a><li><a href="#OS2_device">Ghostscript DLL device for OS/2</a><ul><li><a href="#OS2_bmp"><b><tt>gsdll_get_bitmap()</tt></b></a><li><a href="#OS2_example">Example DLL usage for OS/2</a></ul><li><a href="#Win_device">Ghostscript DLL device for MS Windows</a><ul><li><a href="#Win_copydib"><b><tt>gsdll_copy_dib()</tt></b></a><li><a href="#Win_copypalette"><b><tt>gsdll_copy_palette()</tt></b></a><li><a href="#Win_draw"><b><tt>gsdll_draw()</tt></b></a><li><a href="#Win_get_row"><b><tt>gsdll_get_bitmap_row()</tt></b></a></ul><li><a href="#Win16">Ghostscript DLL Device for 16-bit MS Windows</a></ul> <!-- [1.2 end table of contents] =========================================== --> <!-- [1.3 begin hint] ====================================================== --> <p>For other information, see the <a href="Readme.htm">Ghostscriptoverview</a>. <p><b>WARNING: The API described in this document is obsolete and willbe removed in the future.</b> The current Ghostscript Interpreter API is described in <a href="API.htm">API.htm</a>. <!-- [1.3 end hint] ======================================================== --> <hr> <!-- [1.0 end visible header] ============================================== --> <!-- [2.0 begin contents] ================================================== --> <h2><a name="DLL"></a>What is the Ghostscript DLL?</h2> <p>For the OS/2, Win16 and Win32 platforms, Ghostscript is built as a dynamiclink library (DLL), and to provide the interface described in the <ahref="Use.htm">usage documentation</a>, a smaller independent executable(<b><tt>.EXE</tt></b>) loads this DLL, which provides all the interactionwith the windowing system, including image windows and, if necessary, atext window.  This document describes the DLL interface, which consists ofeight main functions, <a href="#functions">seven platform-independentones</a> provided by the DLL and one, <a href="#Callback">the callbackfunction</a>, provided by the caller.  The DLL provides some otherplatform-specific functions for display devices. <p>The DLL's name and characteristics differ among the three platforms: <ul><li>The <a href="#OS2_device">OS/2 DLL <b><tt>GSDLL2.DLL</tt></b></a> hasMULTIPLE NONSHARED data segments and can be called by multiple programssimultaneously. <li>The <a href="#Win_device">Win32 DLL <b><tt>GSDLL32.DLL</tt></b></a> hasMULTIPLE NONSHARED data segments.  Under Win32s it can be used by only oneprogram at a time, but under Windows 95/98 or Windows NT it can be called bymultiple programs simultaneously. <li>The <a href="#Win16">Win16 DLL <b><tt>GSDLL16.DLL</tt></b></a> is alarge-memory model DLL with far static data.  Due to the limitations of16-bit MS Windows -- Windows 3.n -- the DLL can be used by only one programat a time.</ul> <p>The source for the executable is in <b><tt>dp</tt></b>*.* (OS/2) and<b><tt>dw</tt></b>*.* (Windows).  See these source files for examples ofhow to use the DLL. <hr> <h2><a name="Common_functions"></a>Platform-independent DLL functions</h2> <p>The seven functions provided by the DLL are<ul><li><b><tt>int GSDLLAPI <a href="#revision">gsdll_revision</a>(char **product, char **copyright, long *gs_revision, long *gs_revisiondate)</tt></b><li><b><tt>int GSDLLAPI <a href="#init">gsdll_init</a>(GSDLL_CALLBACK callback, HWND hwnd, int argc, char *argv[]);</tt></b><li><b><tt>int GSDLLAPI <a href="#execute_begin">gsdll_execute_begin</a>(void);</tt></b><li><b><tt>int GSDLLAPI <a href="#execute_cont">gsdll_execute_cont</a>(const char *str, int len);</tt></b><li><b><tt>int GSDLLAPI <a href="#execute_end">gsdll_execute_end</a>(void);</tt></b><li><b><tt>int GSDLLAPI <a href="#exit">gsdll_exit</a>(void);</tt></b><li><b><tt>int GSDLLAPI <a href="#lock_device">gsdll_lock_device</a>(unsigned char *device, int flag);</tt></b> <p>where <b><tt>GSDLLAPI</tt></b> is defined under OS/2 as <blockquote><b><tt>#define GSDLLAPI</tt></b></blockquote> <p>and under MS Windows as <blockquote><b><tt>#define GSDLLAPI CALLBACK _export</tt></b></blockquote></ul> <h3><a name="revision"></a><b><tt>gsdll_revision()</tt></b></h3> <blockquote>This function returns the revision numbers and strings of the GhostscriptDLL; you should call it before <b><tt>gsdll_init()</tt></b> to make surethat the correct version of the Ghostscript DLL has been loaded.  Forexample <blockquote><pre>char *product;char *copyright;long revision;long revisiondate;gsdll_revision(&amp;product, &amp;copyright, &amp;revision, &amp;revisiondate);</pre></blockquote> <p>You may use <b><tt>NULL</tt></b> pointers if you do not want a particularvalue.</blockquote> <h3><a name="init"></a><b><tt>gsdll_init()</tt></b></h3> <blockquote><b><tt>gsdll_init()</tt></b> must be called after loading the DLL andbefore executing any Ghostscript commands.  The arguments are the addressof the callback function, a parent window handle, the count of argumentsand an array of pointers to the arguments.  For example <blockquote><pre>char *argv[5];argv[0] = "gswin.exe";argv[1] = "-Ic:\\gs;c:\gs\\fonts";argv[2] = "-dNOPAUSE",argv[3] = "-sDEVICE=djet500",argv[4] = NULL;argc = 4; code = gsdll_init(gsdll_callback, hwnd, argc, argv);</pre></blockquote> <p><b><tt>hwnd</tt></b> is used as the parent window handle for any windowscreated by Ghostscript.  <b><tt>hwnd</tt></b> may be <b><tt>NULL</tt></b>if the caller has no windows, but if it is <b><tt>NULL</tt></b>, you shouldavoid using devices which may open windows. <p>A return code of 0 (zero) indicates no errors, and the code may now call<b><tt>gsdll_execute_begin()</tt></b> or <b><tt>gsdll_exit()</tt></b>.  Ifthe return value is non-zero then <b><tt>gsdll_exit()</tt></b> must not becalled. <p>A return value of <b><tt>GSDLL_INIT_QUIT</tt></b> indicates that one of thecommand line files or arguments called "<b><tt>quit</tt></b>", or thatGhostscript was reading stdin and reached end-of-file.  This is not anerror.  <b><tt>gsdll_exit()</tt></b> must not be called. <p>A return value of <b><tt>GSDLL_INIT_IN_USE</tt></b> indicates that the DLLis in use by another application (Windows 3.1 only).  The DLL should beimmediately unloaded (or the caller terminated).<b><tt>gsdll_exit()</tt></b> must not be called.</blockquote> <h3><a name="execute_begin"></a><b><tt>gsdll_execute_begin()</tt></b></h3> <blockquote>This must be called after <b><tt>gsdll_init()</tt></b> and before<b><tt>gsdll_execute_cont()</tt></b>.</blockquote> <h3><a name="execute_cont"></a><b><tt>gsdll_execute_cont()</tt></b></h3> <blockquote>After successfully calling <b><tt>gsdll_init()</tt></b> and<b><tt>gsdll_execute_begin()</tt></b>, commands may be given to Ghostscriptwith <b><tt>gsdll_execute_cont()</tt></b>.  Examples are: <blockquote><pre>char *command = "1 2 add == flush\n";code = gsdll_execute_cont(command, strlen(command));command = "qu"code = gsdll_execute_cont(command, strlen(command));command = "it\n"code = gsdll_execute_cont(command, strlen(command));</pre> <a name="cont_returns"></a><table cellpadding=0 cellspacing=0><tr><th colspan=3 bgcolor="#CCCC00"><hr><font size="+1">Return codes from <b><tt>gsdll_execute_cont()</tt></b></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>&lt; 0	<td>&nbsp;	<td>Error<tr valign=top>	<td align=left>&lt;= -100	<td>&nbsp;	<td>"<b><tt>quit</tt></b>" has been executed, or fatal error.<b><tt>gsdll_exit()</tt></b> must then be called: do not call<b><tt>gsdll_execute_end()</tt></b>.</table></blockquote> <b><tt>gsdll_execute_cont()</tt></b>does not flush stdio, so if you want to see output from Ghostscript youmust do this explicitly as shown in the example above. <p>When executing a string with <b><tt>gsdll_execute_cont()</tt></b>,<b><tt>currentfile</tt></b> is the input from<b><tt>gsdll_execute_cont()</tt></b>.  Reading from <b><tt>%stdin</tt></b>uses the callback. <p>Please note that there is a 64 KB length limit on the passed string.If you have more than 65535 bytes of input to process at a given time,it must be split into separate smaller buffers, each passed on a separate call. </blockquote> <h3><a name="execute_end"></a><b><tt>gsdll_execute_end()</tt></b></h3> <blockquote>If <b><tt>gsdll_execute_cont()</tt></b> did not return an error, then<b><tt>gsdll_execute_end()</tt></b> must be called after<b><tt>gsdll_execute_cont()</tt></b> and before<b><tt>gsdll_exit()</tt></b>.</blockquote> <h3><a name="exit"></a><b><tt>gsdll_exit()</tt></b></h3> <blockquote>Call gsdll_exit() to terminate the Ghostscript DLL.  It must be called if afatal error has occurred; see the <a href="#cont_returns">return valueof <b><tt>gsdll_execute_cont()</tt></b></a>.  After calling<b><tt>gsdll_exit()</tt></b>, there are two options: <ul><li>Unload the DLL, either by terminating the application or bycalling <b><tt>DosFreeModule</tt></b> (OS/2) or <b><tt>FreeLibrary</tt></b> (MS Windows). <li>Call <b><tt>gsdll_init()</tt></b> again to restart Ghostscript.</ul></blockquote> <h3><a name="lock_device"></a><b><tt>gsdll_lock_device()</tt></b></h3> <blockquote>Since the caller may be multithreaded, a lock is needed to control accessto the display device, and <b><tt>gsdll_lock_device()</tt></b> provides thatlocking. <blockquote><pre>int gsdll_lock_device(unsigned char *device, int flag); /* Lock the device if flag = TRUE */ /* Unlock the device if flag = FALSE */ /* device is a pointer to Ghostscript os2dll or mswindll device */ /* from GSDLL_DEVICE message. */ /* Return value is the lock count. */</pre> <table cellpadding=0 cellspacing=0><tr><th colspan=3 bgcolor="#CCCC00"><hr><font size="+1">Locking and unlocking devices</font><hr><tr valign=top>	<td>To lock a device	<td>&nbsp;&nbsp;&nbsp;&nbsp;	<td><b><tt>gsdll_lock_device(device, 1)</tt></b>;<tr valign=top>	<td>To unlock a device	<td>&nbsp;	<td><b><tt>gsdll_lock_device(device, 0)</tt></b>;</table></blockquote> <p>This function is typically used to lock the device while repainting awindow or copying the device bitmap to the clipboard.  Ghostscript may drawinto the device bitmap or update the palette entries while the device islocked by the caller, but locking the device prevents the Ghostscript DLLfrom closing the device or changing its size or depth. <p>Under OS/2, Windows 95/98 and Windows NT, this lock is implemented using amutual exclusion semaphore (mutex).  The return value is the lock count,which is either 0 ("unlocked") or 1 ("locked").  The function blocks untilthe device is locked by the caller. <p>Under Win16 or Win32s, <b><tt>gsdll_lock_device()</tt></b> always returnsimmediately with a lock count as its return value.  A lock count of 2 ormore is definite indication of an error, probably calling the functiontwice.  Access to the device should be controlled by checking the Windowsmessage queue only when the bitmap is not being accessed.</blockquote> <hr> <h2><a name="Callback"></a>Callback function</h2> <blockquote>As an argument to <a href="#init"><b><tt>gsdll_init()</tt></b></a> thecaller must provide a callback function which the DLL invokes for stdio andto notify the caller about device events.  The function provided by thecaller has this prototype: <blockquote><b><tt>int gsdll_callback(int&nbsp;message, char&nbsp;*str, unsigned&nbsp;long&nbsp;count);</tt></b></blockquote> <p>The Pascal calling convention is not used.  An example callback functionis: <blockquote><pre>intgsdll_callback(int message, char *str, unsigned long count){char *p;    switch (message) {        case GSDLL_STDIN:            p = fgets(str, count, stdin);            if (p)                return strlen(str);            else                return 0;        case GSDLL_STDOUT:            if (str != (char *)NULL)                fwrite(str, 1, count, stdout);            return count;        case GSDLL_DEVICE:            fprintf(stdout,"Callback: DEVICE %p %s\n", str,                count ? "open" : "close");            break;        case GSDLL_SYNC:            fprintf(stdout,"Callback: SYNC %p\n", str);            break;        case GSDLL_PAGE:            fprintf(stdout,"Callback: PAGE %p\n", str);            break;        case GSDLL_SIZE:            fprintf(stdout,"Callback: SIZE %p width=%d height=%d\n", str,                (int)(count &amp; 0xffff), (int)((count&gt;&gt;16) &amp; 0xffff) );            break;        case GSDLL_POLL:            return 0; /* no error */        default:            fprintf(stdout,"Callback: Unknown message=%d\n",message);            break;    }    return 0;}</pre> <table cellpadding=0 cellspacing=0><tr><th colspan=5 bgcolor="#CCCC00"><hr><font size="+1">Messages used by callback</font><hr><tr valign=bottom>	<th align=left>Symbol	<td>&nbsp;&nbsp;	<th align=left>	<td>&nbsp;&nbsp;	<th align=left>Use<tr>	<td colspan=5><hr><tr valign=top>	<td><b><tt>GSDLL_STDIN</tt></b>	<td>&nbsp;	<td>1	<td>&nbsp;	<td>get <b><tt>count</tt></b> characters to <b><tt>str</tt></b> from stdin, return number of characters read<tr valign=top>	<td><b><tt>GSDLL_STDOUT</tt></b>	<td>&nbsp;	<td>2	<td>&nbsp;	<td>put <b><tt>count</tt></b> characters from <b><tt>str</tt></b>		to stdout, return number of characters written<tr valign=top>	<td><b><tt>GSDLL_DEVICE</tt></b>	<td>&nbsp;	<td>3	<td>&nbsp;	<td>device <b><tt>str</tt></b> has been opened if		<b><tt>count</tt></b>&nbsp;=&nbsp;1, closed if		<b><tt>count</tt></b>&nbsp;=&nbsp;0<tr valign=top>	<td><b><tt>GSDLL_SYNC</tt></b>	<td>&nbsp;	<td>4	<td>&nbsp;	<td>sync_output for device <b><tt>str</tt></b><tr valign=top>	<td><b><tt>GSDLL_PAGE</tt></b>	<td>&nbsp;	<td>5	<td>&nbsp;	<td>output_page for device <b><tt>str</tt></b><tr valign=top>	<td><b><tt>GSDLL_SIZE</tt></b>	<td>&nbsp;	<td>6	<td>&nbsp;	<td>resize for device <b><tt>str</tt></b>:		LOWORD(<b><tt>count</tt></b>) is new <b><tt>xsize</tt></b>,		HIWORD(<b><tt>count</tt></b>) is new <b><tt>ysize</tt></b><tr valign=top>	<td><b><tt>GSDLL_POLL</tt></b>	<td>&nbsp;	<td>7	<td>&nbsp;	<td>Called from <b><tt>gp_check_interrupt()</tt></b><br>		Can be used by the caller to poll the message queue.		Normally returns 0.  To abort		<b><tt>gsdll_execute_cont()</tt></b>, return a non-zero		error code until <b><tt>gsdll_execute_cont()</tt></b>		returns.</table></blockquote></blockquote> <hr> <h2><a name="OS2_device"></a>Ghostscript DLL device for OS/2</h2> <p>The <b><tt>os2dll</tt></b> device is provided in the Ghostscript DLL foruse by the caller.  No drawing facilities are provided by the DLL becausethe DLL may be loaded by a text-only (non-PM) application.  The caller isnotified via the <b><tt>gsdll_callback()</tt></b> when a new<b><tt>os2dll</tt></b> device is opened or closed(<b><tt>GSDLL_DEVICE</tt></b>), when the window should be redrawn(<b><tt>GSDLL_SYNC</tt></b> or <b><tt>GSDLL_PAGE</tt></b>) or when thebitmap size changes (<b><tt>GSDLL_SIZE</tt></b>).Note that more than one <b><tt>os2dll</tt></b> device may be opened. <h3><a name="OS2_bmp"></a><b><tt>gsdll_get_bitmap()</tt></b></h3> <blockquote><b><tt>gsdll_get_bitmap()</tt></b> returns a pointer to a bitmap in BMPformat.  The <b><tt>os2dll</tt></b> device draws into this bitmap. <blockquote><pre>unsigned long gsdll_get_bitmap(unsigned char *device, unsigned char **pbitmap); /* return in pbitmap the address of the bitmap */ /* device is a pointer to Ghostscript os2dll device from GSDLL_DEVICE message */</pre></blockquote> <p>The caller can then display the bitmap however it likes, but should lockthe bitmap with <b><tt>gsdll_lock_device()</tt></b> before painting fromit, and unlock it afterwards.  The bitmap address does not change until the<b><tt>os2dll</tt></b> device is closed; however the bitmap size andpalette may change whenever the bitmap is not locked.</blockquote> <h3><a name="OS2_example"></a>Example DLL usage for OS/2</h3> <p>The example here shows a minimal usage of the Ghostscript DLL under OS/2.The sample callback function above is needed. <blockquote><pre>#define INCL_DOS

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