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<title>libwmf-0.2.0 Tutorial 1: The API</title>
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<h1>libwmf-0.2.0 Tutorial 1: The API</h1>
<h2>Contents</h2>
<ul>
<li><a href="#intro">Introduction</a>
<li><a href="#headers">Header Files</a>
<li><a href="#api">Creating The <b>API</b></a>
<li><a href="#devinit">Acknowledging The Device Layer</a>
<li><a href="#scan">Scanning The Metafile</a>
<li><a href="#devsetup">Setting Up The Device Layer</a>
<li><a href="#play">Playing The Metafile</a>
<li><a href="#font">Fonts & libwmf</a>
<li><a href="#fns">Other <b>API</b> Functions</a>
</ul>
<a name="intro"><h2>Introduction</h2></a>
<p>
The figure below illustrates the tripartite division of <b>application</b>,
<b>interpreter</b>, and <b>device layer</b>. The internal workings of each
of the three is irrelevant; all that matters is the three interfaces which
are separate. The core of <tt>libwmf</tt> is the interpreter, and as such
only the interfaces between (a) the interpreter and the application - the
<b>API</b> - and (b) the interpreter and the device layer - the <b>IPA</b>
- are defined. Applications that wish to implement their own new device
layer are free therefore to define whatever interface is suitable.
</p>
<table align=center><tr><td><img src="wmfpic.png"></td></tr></table>
<p>
<tt>libwmf</tt> includes two device layers: <tt>eps</tt> for conversion to
<tt>EPS</tt> (Encapsulated Postscript) or <tt>PS</tt> (Postscript); and
<tt>gd</tt> for conversion to <tt>PNG</tt> or <tt>JPEG</tt> image formats.
Included with <tt>libwmf</tt> are converters for these: <tt>wmf2eps</tt>
and <tt>wmf2gd</tt> respectively. The source-code for these is an excellent
place to see how to use the various features of the <b>API</b> and device-layer
interfaces.
</p>
<a name="headers"><h2>Header Files</h2></a>
<p>
All libwmf header files are now in a <tt>libwmf</tt> subdirectory. In general
you will need to include two. Unless you are writing a new device layer, which
will be discussed later, you should include only <tt>libwmf/api.h</tt> and the
header for whichever device layer you are interested in, for example:
</p>
<font color=blue>
<pre>
#include <libwmf/api.h>
#include <libwmf/gd.h>
</pre>
</font>
<p>
The <tt>gd</tt> device layer uses the <tt>GD</tt> library, included with
<tt>libwmf</tt>, to output images in <tt>PNG</tt> (or possibly in <tt>JPEG</tt>)
format. Alternatively, if you wish the output to be in <tt>PS</tt> or
<tt>EPS</tt> format, you would include:
</p>
<font color=blue>
<pre>
#include <libwmf/api.h>
#include <libwmf/eps.h>
</pre>
</font>
<a name="api"><h2>Creating The API</h2></a>
<p>
For each metafile you wish to process and convert to a given image type, you
must create an instance of the <b>API</b>. This can be sophisticated or simple.
In its simplest form, the only thing that needs to be specified is which
device layer you wish to use. For example, to use <tt>GD</tt>:
</p>
<font color=blue>
<pre>
wmfAPI_Options options;
wmfAPI* API;
wmf_error_t error;
unsigned long flags;
/* */
flags = WMF_OPT_FUNCTION;
options.function = wmf_gd_function;
/* Other Options */
error = wmf_api_create (&API,flags,&options);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
/* */
</pre>
</font>
<p>
The library performs all memory allocation with respect to the <b>API</b>, and
destroying the instance will free up all associated memory:
</p>
<font color=blue>
<pre>
error = wmf_api_destroy (API);
</pre>
</font>
<p>
There are a number of different options which can be used when creating the
<b>API</b>. The structure of <tt>wmfAPI_Options</tt> is:
</p>
<font color=blue>
<pre>
typedef struct _wmfAPI_Options wmfAPI_Options;
struct _wmfAPI_Options
{ void* context;
void* (*malloc) (void* context,size_t size);
void* (*realloc) (void* context,void* mem,size_t size);
void (*free) (void* context,void* mem);
int argc;
char** argv;
char** fontdirs; /* NULL-terminated list of directories to search for font files */
struct
{ wmfFontMap* wmf; /* {0,*}-terminated list: wmf-font-name -> ps-font-name */
wmfMapping* sub; /* {0,*}-terminated list: wmf-font-name substring equiv */
wmfMapping* ps; /* {0,*}-terminated list: ps-font-name -> pfb-file-name */
} font;
char* sys_fontmap_file;
char* xtra_fontmap_file;
void (*function) (wmfAPI*);
char* module;
char** dirs;
FILE* debug_out;
FILE* error_out;
};
</pre>
</font>
<ul>
<li><b>WMF_OPT_ALLOC</b><br>
If you wish to provide your own memory allocation routines for <tt>libwmf</tt>
to use instead of <tt>malloc</tt>, <tt>realloc</tt> and <tt>free</tt>, these
can be specified:
<font color=blue>
<pre>
flags |= WMF_OPT_ALLOC;
options.context = my_memory_manager_data;
options.malloc = my_malloc;
options.realloc = my_realloc;
options.free = my_free;
</pre>
</font>
<li><b>WMF_OPT_ARGS</b><br>
<tt>libwmf</tt> can be allowed to check for certain command line arguments:
<pre>
--wmf-ignore-nonfatal ignore any non-critical errors or unsupported features
--wmf-error=no suppress error reports
--wmf-debug=no suppress debug reports
--wmf-diagnostics emit diagnostic information (for analysis of metafiles)
--wmf-fontdir=<path> add <path> to list of directories searched for fonts
--wmf-sys-fonts use system fonts, if any found
--wmf-sys-fontmap=<file> use system xml-fontmap file <file> (implies --wmf-sys-fonts)
--wmf-xtra-fonts use non-system fonts, if any found
--wmf-xtra-fontmap=<file> use non-system xml-fontmap file <file> (implies --wmf-xtra-fonts)
</pre>
where the command line is specified by:
<font color=blue>
<pre>
int main (int argc,char** argv)
{ /* */
flags |= WMF_OPT_ARGS;
options.argc = argc;
options.argv = argv;
</pre>
</font>
<li><b>WMF_OPT_FONTDIRS</b><br>
A <b>NULL</b>-terminated list of directories to be searched for fonts can be
specified by:
<font color=blue>
<pre>
char* dirs[3] = { "/usr/share/fonts", "/usr/local/share/fonts", NULL };
/* */
flags |= WMF_OPT_FONTDIRS;
options.fontdirs = dirs;
</pre>
</font>
<li><b>WMF_OPT_FONTMAP</b> [UNTESTED]<br>
This is a system for specifying font mappings; see section on fonts.
<li><b>WMF_OPT_SYS_FONTS</b><br>
Use any system fonts found, not just standard 13.
<li><b>WMF_OPT_SYS_FONTMAP</b> [UNTESTED]<br>
Use specified system XML fontmap file:
<font color=blue>
<pre>
flags |= WMF_OPT_SYS_FONTS;
flags |= WMF_OPT_SYS_FONTMAP;
options.sys_fontmap_file = "/usr/local/share/fonts/fontmap";
</pre>
</font>
<li><b>WMF_OPT_XTRA_FONTS</b><br>
Use any system fonts found, not just standard 13.
<li><b>WMF_OPT_XTRA_FONTMAP</b> [UNTESTED]<br>
Use specified non-system XML fontmap file:
<font color=blue>
<pre>
flags |= WMF_OPT_XTRA_FONTS;
flags |= WMF_OPT_XTRA_FONTMAP;
options.xtra_fontmap_file = "/usr/local/share/libwmf/fonts/fontmap";
</pre>
</font>
<li><b>WMF_OPT_FUNCTION</b><br>
This is how to initialize a device-layer with a supplied function. (Currently
this is the only way to initialize a device layer since modules are not yet
implemented.) The function is device-specific. See above.
<li><b>WMF_OPT_MODULE</b> [UNIMPLEMENTED]<br>
initialize device-layer with specified module
<li><b>WMF_OPT_MODULE_DIRS</b> [UNIMPLEMENTED]<br>
check for module also in specified directories
<li><b>WMF_OPT_IGNORE_NONFATAL</b> [HIGHLY RECOMMENDED]<br>
Ignore (some) non-fatal errors, equivalent to --wmf-ignore-nonfatal
<font color=blue>
<pre>
flags |= WMF_OPT_IGNORE_NONFATAL;
</pre>
</font>
<li><b>WMF_OPT_NO_ERROR</b><br>
Suppress all error reports, equivalent to --wmf-error=no
<font color=blue>
<pre>
flags |= WMF_OPT_NO_ERROR;
</pre>
</font>
<li><b>WMF_OPT_NO_DEBUG</b><br>
Suppress all debug reports, equivalent to --wmf-debug=no
<font color=blue>
<pre>
flags |= WMF_OPT_NO_DEBUG;
</pre>
</font>
<li><b>WMF_OPT_LOG_ERROR</b> [UNTESTED]<br>
Divert error reports to specified stream:
<font color=blue>
<pre>
FILE* e_out;
/* */
e_out = fopen ("error.log","w");
if (e_out)
{ flags |= WMF_OPT_LOG_ERROR;
options.error_out = e_out;
}
</pre>
</font>
<li><b>WMF_OPT_LOG_DEBUG</b> [UNTESTED]<br>
Divert debug reports to specified stream:
<font color=blue>
<pre>
FILE* d_out;
/* */
d_out = fopen ("debug.log","w");
if (d_out)
{ flags |= WMF_OPT_LOG_DEBUG;
options.debug_out = d_out;
}
</pre>
</font>
</ul>
<a name="devinit"><h2>Acknowledging The Device Layer</h2></a>
<p>
In addition to creating the <b>API</b>, <tt>wmf_api_create</tt> sets up the
link with the device layer. Device layer data can be accessed through
<tt>API->device_data</tt>, but the implementation will probably provide a
convenient interface. For example, with <tt>GD</tt>:
</p>
<font color=blue>
<pre>
wmfAPI_Options options;
wmfAPI* API;
wmf_error_t error;
wmf_gd_t* ddata;
unsigned long flags;
/* */
flags = WMF_OPT_FUNCTION | WMF_OPT_IGNORE_NONFATAL;
options.function = wmf_gd_function;
/* Other Options */
error = wmf_api_create (&API,flags,&options);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
ddata = WMF_GD_GetData (API);
if ((ddata->flags & WMF_GD_SUPPORTS_JPEG) == 0)
{ fprintf (stderr,"libwmf does not support JPEG conversion!\n");
wmf_api_destroy (API);
/* */
}
/* */
</pre>
</font>
<p>
At this point there is little need to acknowledge the device layer, except if
(as in the above example) the device layer indicates possible restrictions.
</p>
<a name="scan"><h2>Scanning The Metafile</h2></a>
<p>
Before <i>playing</i> the metafile (i.e., rendering the image) it is necessary
first to open the metafile and second to <i>scan</i> it. To open a metafile
that is a file on disc is simple:
</p>
<font color=blue>
<pre>
error = wmf_file_open (API,"file.wmf");
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
</pre>
</font>
<p>
The file needs to be closed later by calling:
</p>
<font color=blue>
<pre>
error = wmf_file_close (API);
</pre>
</font>
<p>
Alternatively, if the metafile is preloaded in memory, it can be opened with:
</p>
<font color=blue>
<pre>
error = wmf_mem_open (API,(unsigned char*) buffer,(long) buffer_length);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
</pre>
</font>
<p>
and closed later by calling:
</p>
<font color=blue>
<pre>
error = wmf_mem_close (API);
</pre>
</font>
<p>
A third, more generic method is available as well, but requires more work. For
example, to `open' an already-open file stream:
</p>
<font color=blue>
<pre>
int my_wmfRead (void*);
int my_wmfSeek (void*,long);
long my_wmfTell (void*);
/* User redefinable functions for input-stream access:
* wmfRead: returns unsigned char cast to int, or EOF
*/
int my_wmfRead (void* context)
{ return (fgetc ((FILE*) context));
}
/* User redefinable functions for input-stream access:
* wmfSeek: returns (-1) on error, else 0
*/
int my_wmfSeek (void* context,long position)
{ return (fseek ((FILE*) context,position,SEEK_SET));
}
/* User redefinable functions for input-stream access:
* wmfTell: returns (-1) on error, else pos
*/
long my_wmfTell (void* context)
{ return (ftell ((FILE*) context));
}
/* */
error = wmf_bbuf_input (API,my_wmfRead,my_wmfSeek,my_wmfTell,(void*) in);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
</pre>
</font>
<p>
Once the metafile has been opened, it must be scanned. Scanning parses the
metafile without any interaction with the device layer, and its purpose is
(a) determine whether it is a valid metafile, and (b) estimate the dimensions
of the metafile.
</p>
<font color=blue>
<pre>
wmfD_Rect bbox;
/* */
error = wmf_scan (API,0,&bbox);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
</pre>
</font>
<p>
A metafile needs to be scanned, but only once. <tt>wmf_scan</tt> will reject
any further attempts to scan; <tt>wmf_play</tt> (see below) will fail unless
the metafile has been scanned.
</p>
<a name="devsetup"><h2>Setting Up The Device Layer</h2></a>
<p>
Metafiles are basically a vector-graphic format and as such they can be scaled
to any size and aspect ratio. The interpreter describes the metafile in a
scaleable manner to the device layer, and the device layer is free to scale
the metafile in any manner it chooses. As such, the device layer will almost
certainly require (a) the dimensions of the metafile found by <tt>wmf_scan</tt>
(see above), and (b) the image width and height desired by the application.
</p>
<p>
<tt>wmfD_Rect</tt> describes a bounding box in the interpreter's device
coordinates, and is defined as:
</p>
<font color=blue>
<pre>
typedef struct _wmfD_Coord wmfD_Coord;
typedef struct _wmfD_Rect wmfD_Rect;
struct _wmfD_Coord
{ float x;
float y;
};
struct _wmfD_Rect
{ wmfD_Coord TL;
wmfD_Coord BR;
};
</pre>
</font>
<p>
and so an application can determine the image's aspect ratio by:
</p>
<font color=blue>
<pre>
float aspect_ratio;
/* */
aspect_ratio = (bbox.BR.y - bbox.TL.y) / (bbox.BR.x - bbox.TL.x);
</pre>
</font>
<p>
<b>Note: By definition bbox.BR.y > bbox.TL.y and bbox.BR.x > bbox.TL.x</b>
</p>
<p>
Putting this all together, and again using <tt>GD</tt> as an example:
</p>
<font color=blue>
<pre>
wmfAPI_Options options;
wmfAPI* API;
wmfD_Rect bbox;
wmf_error_t error;
wmf_gd_t* ddata;
unsigned long flags;
FILE* out;
/* */
flags = WMF_OPT_FUNCTION | WMF_OPT_IGNORE_NONFATAL;
options.function = wmf_gd_function;
/* Other Options */
error = wmf_api_create (&API,flags,&options);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
ddata = WMF_GD_GetData (API);
if ((ddata->flags & WMF_GD_SUPPORTS_JPEG) == 0)
{ fprintf (stderr,"libwmf does not support JPEG conversion!\n");
wmf_api_destroy (API);
/* */
}
error = wmf_file_open (API,"file.wmf");
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
error = wmf_scan (API,0,&bbox);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
out = fopen ("file.jpeg","w");
if (out == 0)
{ wmf_api_destroy (API);
/* */
}
ddata->type = wmf_gd_jpeg;
ddata->flags |= WMF_GD_OUTPUT_FILE;
ddata->file = out;
ddata->bbox = bbox;
ddata->width = (unsigned int) ceil (ddata->bbox.BR.x - ddata->bbox.TL.x);
ddata->height = (unsigned int) ceil (ddata->bbox.BR.y - ddata->bbox.TL.y);
</pre>
</font>
<p>
The above example doesn't do anything intelligent with the size of the image.
The converter <tt>wmf2gd</tt> sets a maximum size and scales the image
accordingly.
</p>
<a name="play"><h2>Playing The Metafile</h2></a>
<p>
The final step is simply to play the metafile:
</p>
<font color=blue>
<pre>
error = wmf_play (API,0,0);
if (error != wmf_E_None)
{ wmf_api_destroy (API);
/* */
}
</pre>
</font>
<p>
This can be done any number of times, with varying device layer settings if
desired.
</p>
<a name="font"><h2>Fonts & libwmf</h2></a>
<p>
There are a number of issues with fonts and <tt>libwmf</tt> to complicate
matters: the first is the need to translate font names specified into font
names recognized by <tt>libwmf</tt>; the second is to find the corresponding
font files; a third is to work out what encoding (char. set) to use. Described
below is <tt>libwmf</tt>'s native mechanism for dealing with these issues.
While versatile, unfortunately it requires significant effort on the part of an
application that seeks to extend the limited font mapping provided by default.
A second (experimental and optional) mechanism is provided also, and this reads
an XML file containing font information (file locations and font names); on
RedHat Linux systems this file is <tt>/usr/share/fonts/fontmap</tt>. No doubt
this is an area that will see considerable future development.
</p>
<p>
Chances are, the metafile will require fonts that are not available to
<tt>libwmf</tt>, and there must be a mechanism, therefore, for translating
metafile fontnames into usable fonts. As noted above, the
<tt>wmfAPI_Options</tt> structure passed to <tt>wmf_api_create</tt> has the
following entries:
</p>
<font color=blue>
<pre>
typedef struct _wmfAPI_Options wmfAPI_Options;
struct _wmfAPI_Options
{ /* */
struct
{ wmfFontMap* wmf; /* {0,*}-terminated list: wmf-font-name -> ps-font-name */
wmfMapping* sub; /* {0,*}-terminated list: wmf-font-name substring equiv */
wmfMapping* ps; /* {0,*}-terminated list: ps-font-name -> pfb-file-name */
} font;
/* */
}
</pre>
</font>
<p>
The two mapping types are defined:
</p>
<font color=blue>
<pre>
typedef struct _wmfMapping wmfMapping;
typedef struct _wmfFontMap wmfFontMap;
struct _wmfMapping
{ char* name;
char* mapping;
FT_Encoding encoding;
};
struct _wmfFontMap
{ char* name; /* wmf font name */
char* normal; /* postscript font names */
char* italic;
char* bold;
char* bolditalic;
};
</pre>
</font>
<p>
Internally <tt>libwmf</tt> has the following default definitions:
</p>
<font color=blue>
<pre>
/* postscript (standard 13) font name mapping to type 1 font file
*/
static wmfMapping PSFontMap[13] = {
{ "Courier", "n022003l.pfb", ft_encoding_adobe_standard },
{ "Courier-Oblique", "n022023l.pfb", ft_encoding_adobe_standard },
{ "Courier-Bold", "n022004l.pfb", ft_encoding_adobe_standard },
{ "Courier-BoldOblique", "n022024l.pfb", ft_encoding_adobe_standard },
{ "Helvetica", "n019003l.pfb", ft_encoding_adobe_standard },
{ "Helvetica-Oblique", "n019023l.pfb", ft_encoding_adobe_standard },
{ "Helvetica-Bold", "n019004l.pfb", ft_encoding_adobe_standard },
{ "Helvetica-BoldOblique","n019024l.pfb", ft_encoding_adobe_standard },
{ "Times-Roman", "n021003l.pfb", ft_encoding_adobe_standard },
{ "Times-Italic", "n021023l.pfb", ft_encoding_adobe_standard },
{ "Times-Bold", "n021004l.pfb", ft_encoding_adobe_standard },
{ "Times-BoldItalic", "n021024l.pfb", ft_encoding_adobe_standard },
{ "Symbol", "s050000l.pfb", ft_encoding_adobe_custom }};
/* exact WMF font name to postscript (standard 13) equivalent...
* well, yeah, I know. :-(
*/
static wmfFontMap WMFFontMap[] = {
{ "Courier", "Courier", "Courier-Oblique", "Courier-Bold", "Courier-BoldOblique" },
{ "Helvetica", "Helvetica", "Helvetica-Oblique", "Helvetica-Bold", "Helvetica-BoldOblique" },
{ "Modern", "Courier", "Courier-Oblique", "Courier-Bold", "Courier-BoldOblique" },
{ "Monotype Corsiva", "Courier", "Courier-Oblique", "Courier-Bold", "Courier-BoldOblique" },
{ "News Gothic", "Helvetica", "Helvetica-Oblique", "Helvetica-Bold", "Helvetica-BoldOblique" },
{ "Symbol", "Symbol", "Symbol", "Symbol", "Symbol" },
{ "System", "Courier", "Courier-Oblique", "Courier-Bold", "Courier-BoldOblique" },
{ "Times", "Times-Roman", "Times-Italic", "Times-Bold", "Times-BoldItalic" }};
/* Sub-string match if not in the above list;
*/
static wmfMapping SubFontMap[] = {
{ "Arial", "Helvetica" },
{ "Courier", "Courier" },
{ "Fixed", "Courier" },
{ "Helvetica", "Helvetica" },
{ "Sans", "Helvetica" },
{ "Sym", "Symbol" },
{ "Terminal", "Courier" },
{ "Times", "Times" },
{ "Wingdings", "Symbol" }};
/* If all else fails, assume Times
*/
static char* DefaultFontMapping = "Times";
</pre>
</font>
<p>
Bundled with <tt>libwmf</tt> are the thirteen standard <tt>ghostscript</tt>
fonts. Unless the application specifies other fonts, <tt>libwmf</tt> will
attempt to map the metafile's font name to one of these default fonts.
</p>
<p>
First an exact match is sought with the first argument of each font in
<tt>WMFFontMap</tt>. For example, "News Gothic" would be an exact match;
"Arial" would not. If there is no exact match, then a substring search is
performed against the first argument of each font in <tt>SubFontMap</tt>.
For example, this time "Arial" would match; "Zapf Chancery" would not. If
there is still no exact match then "Times" is assumed.
</p>
<p>
Once a font name is found, this is converted to an equivalent name, assumed to
be the postscript font name, using <tt>WMFFontMap</tt>. And finally the
equivalent name is searched for in <tt>PSFontMap</tt>. For example,
"Zapf Chancery" in italics would be mapped to "Times" in italics, then to
"Times-Italic", and finally to "n021023l.pfb".
</p>
<p>
<tt>libwmf</tt> searches through the list of font directories for this file
and loads it using <tt>freetype (2)</tt> with the encoding specified by the
third argument of the <tt>PSFontMap</tt> entry.
</p>
<p>
These three lists can be prepended by using the <b>WMF_OPT_FONTMAP</b> option.
The font files can be any format supported by <tt>freetype (2)</tt>.
</p>
<p>
After the metafile has been scanned, <tt>API->fonts</tt> is a
<tt>NULL</tt>-terminated list of (postscript) font names corresponding to the
fonts selected by the interpreter.
</p>
<a name="fns"><h2>Other API Functions</h2></a>
<p>
<tt>libwmf</tt> performs all memory allocation with respect to the <b>API</b>.
When the <b>API</b> is destroyed, all associated memory is freed. The routines
for allocating and freeing such memory are:
</p>
<font color=blue>
<pre>
extern void* wmf_malloc (wmfAPI*,size_t);
extern void* wmf_calloc (wmfAPI*,size_t,size_t);
extern void* wmf_realloc (wmfAPI*,void*,size_t);
extern void wmf_free (wmfAPI*,void*);
</pre>
</font>
<p>
These behave similarly to the standard <tt>malloc</tt>, etc. Similarly:
</p>
<font color=blue>
<pre>
extern char* wmf_strdup (wmfAPI*,char*);
</pre>
</font>
<p>
is an internal implementation of <tt>strdup</tt> which allocates the copied
string w.r.t. the <b>API</b>. On a related note,
</p>
<font color=blue>
<pre>
extern char* wmf_strstr (const char*,const char*);
</pre>
</font>
<p>
is an internal implementation of <tt>strstr</tt> and may be just a wrapper for
it. This is a special case of a function which does not refer to the
<b>API</b>.
</p>
<p>
Messages can be added to the <i>error</i> and <i>debug</i> streams using:
</p>
<font color=blue>
<pre>
extern void wmf_error (wmfAPI* API,char* srcfilename,int linenumber,char* message);
extern void wmf_debug (wmfAPI* API,char* srcfilename,int linenumber,char* message);
extern void wmf_assert (wmfAPI* API,char* srcfilename,int linenumber);
</pre>
</font>
<p>
but these functions should be used via the macros <tt>WMF_ERROR(API,"mesg")</tt>,
<tt>WMF_DEBUG(API,"mesg")</tt>, and <tt>WMF_ASSERT(API,<expr>)</tt>.
</p>
<p>
Finally, a call-back function can be set. This is called after each metafile
record with an estimate of the proportion of the metafile read; if the return
value is non-zero then the player will exit prematurely.
</p>
<font color=blue>
<pre>
typedef int (*wmfStatus) (void* context,float proportion);
extern void wmf_status_function (wmfAPI* API,void* context,wmfStatus function);
</pre>
</font>
<p>
For example, the following status function is used by <tt>wmf2gd</tt>:
</p>
<font color=blue>
<pre>
int wmf2gd_status (void* context,float p)
{ int percent;
percent = (int) (p * 100);
if (percent < 0) percent = 0;
if (percent > 99) percent = 99;
fprintf (stderr,"%2d%%\b\b\b",percent);
}
</pre>
</font>
<p>
Although there are other functions in the <b>API</b>, their use is <i>not</i>
recommended.
</p>
<hr>
<address>
Copyright 2001 wvWare/libwmf <a href="http://www.wvware.com/">http://www.wvware.com/</a>
</address>
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