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diff --git a/doc/DLL.htm b/doc/DLL.htm deleted file mode 100644 index b1a7ecfb6..000000000 --- a/doc/DLL.htm +++ /dev/null @@ -1,754 +0,0 @@ -<!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" href="images/favicon.svg"> - <title>How to Use the Ghostscript Dynamic Link Library (DLL)</title> - <link href="default.css" rel="stylesheet" type="text/css"> -</head> - -<body> - <header><div class="title"><a href="index.html"><h1 aria-label="title">Ghostscript documentation</h1><h2 aria-label="version"></h2></a></div><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>How to Use the Ghostscript Dynamic Link Library (DLL)</h1> - -<h2><a name="toc"></a>Table of contents</h2> -<ul class="toc"> - <li><a href="#DLL">What is the Ghostscript DLL?</a></li> - <li><a href="#Common_functions">Platform-independent DLL functions</a></li> - <li> - <ul> - <li><a href="#revision"><code>gsdll_revision()</code></a></li> - <li><a href="#init"><code>gsdll_init()</code></a></li> - <li><a href="#execute_begin"><code>gsdll_execute_begin()</code></a></li> - <li><a href="#execute_cont"><code>gsdll_execute_cont()</code></a></li> - <li><a href="#execute_end"><code>gsdll_execute_end()</code></a></li> - <li><a href="#exit"><code>gsdll_exit()</code></a></li> - <li><a href="#lock_device"><code>gsdll_lock_device()</code></a></li> - </ul> - </li> - <li><a href="#Callback">Callback function</a></li> - <li><a href="#OS2_device">Ghostscript DLL device for OS/2</a></li> - <li> - <ul> - <li><a href="#OS2_bmp"><code>gsdll_get_bitmap()</code></a></li> - <li><a href="#OS2_example">Example DLL usage for OS/2</a></li> - </ul> - </li> - <li><a href="#Win_device">Ghostscript DLL device for MS Windows</a></li> - <li> - <ul> - <li><a href="#Win_copydib"><code>gsdll_copy_dib()</code></a></li> - <li><a href="#Win_copypalette"><code>gsdll_copy_palette()</code></a></li> - <li><a href="#Win_draw"><code>gsdll_draw()</code></a></li> - <li><a href="#Win_get_row"><code>gsdll_get_bitmap_row()</code></a></li> - </ul> - </li> - <li><a href="#Win16">Ghostscript DLL Device for 16-bit MS Windows</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> -<b>WARNING: The API described in this document is obsolete and will -be 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 dynamic -link library (DLL), and to provide the interface described in the <a -href="Use.htm">usage documentation</a>, a smaller independent executable -(<code>.EXE</code>) loads this DLL, which provides all the interaction -with the windowing system, including image windows and, if necessary, a -text window. This document describes the DLL interface, which consists of -eight main functions, <a href="#functions">seven platform-independent -ones</a> provided by the DLL and one, <a href="#Callback">the callback -function</a>, provided by the caller. The DLL provides some other -platform-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 <code>GSDLL2.DLL</code></a> has -MULTIPLE NONSHARED data segments and can be called by multiple programs -simultaneously.</li> - -<li>The <a href="#Win_device">Win32 DLL <code>GSDLL32.DLL</code></a> has -MULTIPLE NONSHARED data segments. Under Win32s it can be used by only one -program at a time, but under Windows 95/98 or Windows NT it can be called by -multiple programs simultaneously.</li> - -<li>The <a href="#Win16">Win16 DLL <code>GSDLL16.DLL</code></a> is a -large-memory model DLL with far static data. Due to the limitations of -16-bit MS Windows -- Windows 3.n -- the DLL can be used by only one program -at a time.</li> -</ul> - -<p> -The source for the executable is in <code>dp</code>*.* (OS/2) and -<code>dw</code>*.* (Windows). See these source files for examples of -how 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><code>int GSDLLAPI <a href="#revision">gsdll_revision</a>(char **product, char **copyright, long *gs_revision, long *gs_revisiondate)</code></li> -<li><code>int GSDLLAPI <a href="#init">gsdll_init</a>(GSDLL_CALLBACK callback, HWND hwnd, int argc, char *argv[]);</code></li> -<li><code>int GSDLLAPI <a href="#execute_begin">gsdll_execute_begin</a>(void);</code></li> -<li><code>int GSDLLAPI <a href="#execute_cont">gsdll_execute_cont</a>(const char *str, int len);</code></li> -<li><code>int GSDLLAPI <a href="#execute_end">gsdll_execute_end</a>(void);</code></li> -<li><code>int GSDLLAPI <a href="#exit">gsdll_exit</a>(void);</code></li> -<li><code>int GSDLLAPI <a href="#lock_device">gsdll_lock_device</a>(unsigned char *device, int flag);</code> - -<p> -where <code>GSDLLAPI</code> is defined under OS/2 as - -<blockquote><code> -#define GSDLLAPI -</code></blockquote> - -<p> -and under MS Windows as - -<blockquote><code> -#define GSDLLAPI CALLBACK _export -</code></blockquote> -</li> -</ul> - -<h3><a name="revision"></a><code>gsdll_revision()</code></h3> - -<blockquote> -This function returns the revision numbers and strings of the Ghostscript -DLL; you should call it before <code>gsdll_init()</code> to make sure -that the correct version of the Ghostscript DLL has been loaded. For -example - -<blockquote> -<pre>char *product; -char *copyright; -long revision; -long revisiondate; -gsdll_revision(&product, &copyright, &revision, &revisiondate); -</pre></blockquote> - -<p> -You may use <code>NULL</code> pointers if you do not want a particular -value. -</blockquote> - -<h3><a name="init"></a><code>gsdll_init()</code></h3> - -<blockquote> -<code>gsdll_init()</code> must be called after loading the DLL and -before executing any Ghostscript commands. The arguments are the address -of the callback function, a parent window handle, the count of arguments -and 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> -<code>hwnd</code> is used as the parent window handle for any windows -created by Ghostscript. <code>hwnd</code> may be <code>NULL</code> -if the caller has no windows, but if it is <code>NULL</code>, you should -avoid using devices which may open windows. - -<p> -A return code of 0 (zero) indicates no errors, and the code may now call -<code>gsdll_execute_begin()</code> or <code>gsdll_exit()</code>. If -the return value is non-zero then <code>gsdll_exit()</code> must not be -called. - -<p> -A return value of <code>GSDLL_INIT_QUIT</code> indicates that one of the -command line files or arguments called "<code>quit</code>", or that -Ghostscript was reading stdin and reached end-of-file. This is not an -error. <code>gsdll_exit()</code> must not be called. - -<p> -A return value of <code>GSDLL_INIT_IN_USE</code> indicates that the DLL -is in use by another application (Windows 3.1 only). The DLL should be -immediately unloaded (or the caller terminated). -<code>gsdll_exit()</code> must not be called. -</blockquote> - -<h3><a name="execute_begin"></a><code>gsdll_execute_begin()</code></h3> - -<blockquote> -This must be called after <code>gsdll_init()</code> and before -<code>gsdll_execute_cont()</code>. -</blockquote> - -<h3><a name="execute_cont"></a><code>gsdll_execute_cont()</code></h3> - -<blockquote> -After successfully calling <code>gsdll_init()</code> and -<code>gsdll_execute_begin()</code>, commands may be given to Ghostscript -with <code>gsdll_execute_cont()</code>. 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> -<tr> - <th colspan="2">Return codes from gsdll_execute_cont()</th> -</tr> -<tr> - <th align="left">Code</th> - - <th align="left">Status</th> -</tr> -<tr> - <td align="left">0</td> - - <td>No errors</td> - </tr> -<tr> - <td align="left">< 0</td> - - <td>Error</td> - </tr> -<tr> - <td align="left"><= -100</td> - - <td>"<code>quit</code>" has been executed, or fatal error. -<code>gsdll_exit()</code> must then be called: do not call -<code>gsdll_execute_end()</code>.</td> - </tr> -</table> -</blockquote> - -<code>gsdll_execute_cont()</code> -does not flush stdio, so if you want to see output from Ghostscript you -must do this explicitly as shown in the example above. - -<p> -When executing a string with <code>gsdll_execute_cont()</code>, -<code>currentfile</code> is the input from -<code>gsdll_execute_cont()</code>. Reading from <code>%stdin</code> -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><code>gsdll_execute_end()</code></h3> - -<blockquote> -If <code>gsdll_execute_cont()</code> did not return an error, then -<code>gsdll_execute_end()</code> must be called after -<code>gsdll_execute_cont()</code> and before -<code>gsdll_exit()</code>. -</blockquote> - -<h3><a name="exit"></a><code>gsdll_exit()</code></h3> - -<blockquote> -Call gsdll_exit() to terminate the Ghostscript DLL. It must be called if a -fatal error has occurred; see the <a href="#cont_returns">return value -of <code>gsdll_execute_cont()</code></a>. After calling -<code>gsdll_exit()</code>, there are two options: - -<ul> -<li>Unload the DLL, either by terminating the application or by -calling <code>DosFreeModule</code> (OS/2) or <code>FreeLibrary</code> (MS Windows). - -<li>Call <code>gsdll_init()</code> again to restart Ghostscript. -</ul> -</blockquote> - -<h3><a name="lock_device"></a><code>gsdll_lock_device()</code></h3> - -<blockquote> -Since the caller may be multithreaded, a lock is needed to control access -to the display device, and <code>gsdll_lock_device()</code> provides that -locking. - -<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> -<tr> - <th colspan="2">Locking and unlocking devices</th> - </tr> -<tr> - <td>To lock a device</td> - - <td><code>gsdll_lock_device(device, 1)</code>;</td> - </tr> -<tr> - <td>To unlock a device</td> - - <td><code>gsdll_lock_device(device, 0)</code>;</td> - </tr> -</table> -</blockquote> - -<p> -This function is typically used to lock the device while repainting a -window or copying the device bitmap to the clipboard. Ghostscript may draw -into the device bitmap or update the palette entries while the device is -locked by the caller, but locking the device prevents the Ghostscript DLL -from closing the device or changing its size or depth. - -<p> -Under OS/2, Windows 95/98 and Windows NT, this lock is implemented using a -mutual exclusion semaphore (mutex). The return value is the lock count, -which is either 0 ("unlocked") or 1 ("locked"). The function blocks until -the device is locked by the caller. - -<p> -Under Win16 or Win32s, <code>gsdll_lock_device()</code> always returns -immediately with a lock count as its return value. A lock count of 2 or -more is definite indication of an error, probably calling the function -twice. Access to the device should be controlled by checking the Windows -message 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"><code>gsdll_init()</code></a> the -caller must provide a callback function which the DLL invokes for stdio and -to notify the caller about device events. The function provided by the -caller has this prototype: - -<blockquote><code> -int gsdll_callback(int message, char *str, unsigned long count); -</code></blockquote> - -<p> -The Pascal calling convention is not used. An example callback function -is: - -<blockquote> -<pre>int -gsdll_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 & 0xffff), (int)((count>>16) & 0xffff) ); - break; - case GSDLL_POLL: - return 0; /* no error */ - default: - fprintf(stdout,"Callback: Unknown message=%d\n",message); - break; - } - return 0; -} -</pre> - -<table> - <tr> - <th colspan="3">Messages used by callback</th> - </tr> -<tr> - <th align="left">Symbol</th> - - <th align="left">Value</th> - - <th align="left">Use</th> - </tr> -<tr> - <td><code>GSDLL_STDIN</code></td> - - <td>1</td> - - <td>get <code>count</code> characters to <code>str</code> from stdin, return number of characters read</td> - </tr> -<tr> - <td><code>GSDLL_STDOUT</code></td> - - <td>2</td> - - <td>put <code>count</code> characters from <code>str</code> - to stdout, return number of characters written</td> - </tr> -<tr> - <td><code>GSDLL_DEVICE</code></td> - - <td>3</td> - - <td>device <code>str</code> has been opened if - <code>count</code> = 1, closed if - <code>count</code> = 0</td> - </tr> -<tr> - <td><code>GSDLL_SYNC</code></td> - - <td>4</td> - - <td>sync_output for device <code>str</code></td> - </tr> -<tr> - <td><code>GSDLL_PAGE</code></td> - - <td>5</td> - - <td>output_page for device <code>str</code></td> - </tr> -<tr> - <td><code>GSDLL_SIZE</code></td> - - <td>6</td> - - <td>resize for device <code>str</code>: - LOWORD(<code>count</code>) is new <code>xsize</code>, - HIWORD(<code>count</code>) is new <code>ysize</code></td> - </tr> -<tr> - <td><code>GSDLL_POLL</code></td> - - <td>7</td> - - <td>Called from <code>gp_check_interrupt()</code><br> - Can be used by the caller to poll the message queue. - Normally returns 0. To abort - <code>gsdll_execute_cont()</code>, return a non-zero - error code until <code>gsdll_execute_cont()</code> - returns.</td> - </tr> -</table> -</blockquote> -</blockquote> - -<hr> - -<h2><a name="OS2_device"></a>Ghostscript DLL device for OS/2</h2> - -<p> -The <code>os2dll</code> device is provided in the Ghostscript DLL for -use by the caller. No drawing facilities are provided by the DLL because -the DLL may be loaded by a text-only (non-PM) application. The caller is -notified via the <code>gsdll_callback()</code> when a new -<code>os2dll</code> device is opened or closed -(<code>GSDLL_DEVICE</code>), when the window should be redrawn -(<code>GSDLL_SYNC</code> or <code>GSDLL_PAGE</code>) or when the -bitmap size changes (<code>GSDLL_SIZE</code>). -Note that more than one <code>os2dll</code> device may be opened. - -<h3><a name="OS2_bmp"></a><code>gsdll_get_bitmap()</code></h3> - -<blockquote> -<code>gsdll_get_bitmap()</code> returns a pointer to a bitmap in BMP -format. The <code>os2dll</code> 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 lock -the bitmap with <code>gsdll_lock_device()</code> before painting from -it, and unlock it afterwards. The bitmap address does not change until the -<code>os2dll</code> device is closed; however the bitmap size and -palette 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 -#include <os2.h> -#include <stdio.h> -#include "gsdll.h" - -PFN_gsdll_init pgsdll_init; -PFN_gsdll_execute_begin pgsdll_execute_begin; -PFN_gsdll_execute_cont pgsdll_execute_cont; -PFN_gsdll_execute_end pgsdll_execute_end; -PFN_gsdll_exit pgsdll_exit; - -HMODULE hmodule_gsdll; -char buf[256]; - -int -main(int argc, char *argv[]) -{ -int code; -APIRET rc; - if (!DosLoadModule(buf, sizeof(buf), "GSDLL2", &hmodule_gsdll)) { - fprintf(stderr, "Loaded GSDLL2\n"); - DosQueryProcAddr(hmodule_gsdll, 0, "gsdll_init", (PFN *)(&pgsdll_init)); - DosQueryProcAddr(hmodule_gsdll, 0, "gsdll_execute_begin", (PFN *)(&pgsdll_execute_begin)); - DosQueryProcAddr(hmodule_gsdll, 0, "gsdll_execute_cont", (PFN *)(&pgsdll_execute_cont)); - DosQueryProcAddr(hmodule_gsdll, 0, "gsdll_execute_end", (PFN *)(&pgsdll_execute_end)); - DosQueryProcAddr(hmodule_gsdll, 0, "gsdll_exit", (PFN *)(&pgsdll_exit)); - } - else { - fprintf(stderr, "Can't load GSDLL2\n"); - } - - code = (*pgsdll_init)(gsdll_callback, NULL, argc, argv); - fprintf(stdout,"gsdll_init returns %d\n", code); - code = (*pgsdll_execute_begin)(); - if (code==0) { - while (fgets(buf, sizeof(buf), stdin)) { - code = (*pgsdll_execute_cont)(buf, strlen(buf)); - fprintf(stdout,"gsdll_execute returns %d\n", code); - if (code < 0) - break; - } - if (!code) - code = (*pgsdll_execute_end)(); - code = (*pgsdll_exit)(); - fprintf(stdout,"gsdll_exit returns %d\n", code); - } - rc = DosFreeModule(hmodule_gsdll); - fprintf(stdout,"DosFreeModule returns %d\n", rc); - return 0; -} -</pre></blockquote> - -<hr> - -<h2><a name="Win_device"></a>Ghostscript DLL device for MS Windows</h2> - -<p> -The <code>mswindll</code> device is provided in the Ghostscript DLL for -use by the caller. The caller is notified via the -<code>gsdll_callback()</code> when a new <code>mswindll</code> device -is opened or closed (<code>GSDLL_DEVICE</code>), when the window should -be redrawn (<code>GSDLL_SYNC</code> or <code>GSDLL_PAGE</code>) or -when the bitmap size changes (<code>GSDLL_SIZE</code>). Note that more -than one <code>mswindll</code> device may be opened. - -<p> -Four DLL functions are available to use the <code>mswindll</code> -device. - -<h3><a name="Win_copydib"></a><code>gsdll_copy_dib()</code></h3> - -<blockquote> -Copy the <code>mswindll</code> bitmap to the clipboard. - -<blockquote> -<pre>HGLOBAL GSDLLAPI gsdll_copy_dib(unsigned char *device); - /* make a copy of the device bitmap and return shared memory handle to it */ - /* device is a pointer to Ghostscript device from GSDLL_DEVICE message */ -</pre></blockquote> -</blockquote> - -<h3><a name="Win_copypalette"></a><code>gsdll_copy_palette()</code></h3> - -<blockquote> -Copy the <code>mswindll</code> palette to the clipboard. - -<blockquote> -<pre>HPALETTE GSDLLAPI gsdll_copy_palette(unsigned char *device); -/* make a copy of the device palette and return a handle to it */ -/* device is a pointer to Ghostscript device from GSDLL_DEVICE message */ -</pre></blockquote> -</blockquote> - -<h3><a name="Win_draw"></a><code>gsdll_draw()</code></h3> - -<blockquote> -Display output from the <code>mswindll</code> device. The caller should -create a window and call <code>gsdll_draw()</code> in response to the -<code>WM_PAINT</code> message. The device context <code>hdc</code> -must be for a device because <code>SetDIBitsToDevice()</code> is used. - -<blockquote> -<pre>void GSDLLAPI gsdll_draw(unsigned char *device, HDC hdc, - LPRECT dest, LPRECT src); -/* copy the rectangle src from the device bitmap */ -/* to the rectangle dest on the device given by hdc */ -/* hdc must be a device context for a device (NOT a bitmap) */ -/* device is a pointer to Ghostscript device from GSDLL_DEVICE message */ -</pre></blockquote> -</blockquote> - -<h3><a name="Win_get_row"></a><code>gsdll_get_bitmap_row()</code></h3> - -<blockquote> -Get a BMP header, a palette, and a pointer to a row in the bitmap. This -function exists to allow the bitmap to be copied to a file or structured -storage without the overhead of having two copies of the bitmap in memory -at the same time. - -<p> -Ghostscript can change the palette while the device is locked. Do not call -this function while Ghostscript is busy. - -<blockquote> -<pre>int GSDLLAPI gsdll_get_bitmap_row(unsigned char *device, LPBITMAPINFOHEADER pbmih, - LPRGBQUAD prgbquad, LPBYTE *ppbyte, unsigned int row) -/* If pbmih nonzero, copy the BITMAPINFOHEADER. - * If prgbquad nonzero, copy the palette. - * number of entries copied is given by pbmih->biClrUsed - * If ppbyte nonzero, return pointer to row. - * pointer is only valid while device is locked - */ -</pre></blockquote> -</blockquote> - -<hr> - -<h2><a name="Win16"></a>Ghostscript DLL Device for 16-bit MS Windows</h2> - -<p> -This platform has the most problems of the three. Support for it may be -dropped in future. - -<p> -The Win16 DLL <code>GSDLL16.DLL</code> is a large-memory model DLL with -far static data. Due to the limitations of 16-bit MS Windows, the DLL can -be used by only one program at a time. - -<p> -However, <code>GSDLL16</code> is marked as having SINGLE SHARED data -segments, allowing multiple applications to load it with no error -indication. (The DLL wouldn't load at all if MULTIPLE NONSHARED was used). -Nonetheless, <b>it cannot be used by more than one application at a -time</b>, so applications loading <code>GSDLL16</code> should check the -return value of <code>gsdll_init()</code>: if this value is non-zero, -then <code>GSDLL16</code> is already in use by another application and -should <b><em>not</em></b> be used: <code>GSDLL16</code> should be -unloaded immediately using <code>FreeLibrary()</code>, or the calling -program should quit without attempting to use the library.. - -<p> -The segmented architecture of the Intel 80286 causes the usual amount of -grief when using <code>GSDLL16</code>. Because the callback is called -from the DLL, which is using a different data segment, the callback must be -declared as <code>_far _export</code>: - -<blockquote> -<pre>int _far _export gsdll_callback(int message, char *str, unsigned long count); -</pre></blockquote> - -<p> -Instead of giving <code>gsdll_init()</code> the address of -<code>gsdll_callback()</code>, it should instead be given the address of -a thunk created by <code>MakeProcInstance</code>. This thunk changes -the data segment back to that used by the caller: - -<blockquote> -<pre>FARPROC lpfnCallback; -lpfnCallback = (FARPROC)MakeProcInstance((FARPROC)gsdll_callback, hInstance); -code = (*pgsdll_init)((GSDLL_CALLBACK)lpfnCallback, NULL, argc, argv); -if (!code) { - fprintf(stderr, "GSDLL16 is already in use\n"); - return -1; -} -</pre></blockquote> - -<!-- [2.0 end contents] ==================================================== --> - -<!-- [3.0 begin visible trailer] =========================================== --> -<hr> - -<p> -<small>Copyright © 2000-2022 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. 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