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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<TITLE>XmHTML Programmers Manual: XmHTMLImageDefaultProc</TITLE>
<META HTTP-EQUIV="Keywords" CONTENT="XmHTML, HTML, Motif, Widget, eXode, XntHelp, Linux">
<META HTTP-EQUIV="Reply-to" CONTENT="ripley@xs4all.nl">
<META HTTP-EQUIV="Description" CONTENT="XmHTMLImageDefaultProc - XmHTML default image loading function.">
<META NAME="Author" CONTENT="Koen D'Hondt">
<META NAME="Copyright" content="1995-1997 by Ripley Software Development">
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<h3><font face="helvetica,arial">Name</font></h3>
<blockquote>
XmHTMLImageDefaultProc - XmHTML default image loading function
</blockquote>
<h3><font face="helvetica,arial">Synopsis</font></h3>
<blockquote>
XmImageInfo *XmHTMLImageDefaultProc(Widget w, String file,
unsigned char *buf, int size)
</blockquote>
<h3><font face="helvetica,arial">Description</font></h3>
<blockquote>
XmHTMLImageDefaultProc is the default image loading function of a XmHTML
widget. By default, this function is capable of decoding X11 bitmaps (xbm),
X11 pixmaps (xpm) and GIF87a and GIF89a images and animations.
<p>
Support for JPEG, PNG and GZF images is a compile time option and as such
may or may not be present in your version of the XmHTML library.
<p>
The value returned by this function is a structure containing all the
information a XmHTML widget requires to create the image and can be
used as the return value for the callback resource installed on the
XmNimageProc resource.
<p>
<dl>
<dt>w
<dd>Specifies the parent Widget ID. This must be a widget of class
xmHTMLWidgetClass;
<dt>file
<dd>if <i>size</i> is 0, the full path of the image to be decoded.
If <i>buf</i> and <i>size</i> are non-zero, the original url of
the image that is to be loaded. This argument may never be NULL.
<dt>buf
<dd>preloaded image data. The size of this data is given by the
<i>size</i> argument and is ignored if the <i>size</i> argument
is zero.
<dt>size
<dd>size of the preloaded image data. This argument is ignored if
<i>buf</i> is NULL.
</dl>
<p>
If size and/or buf is NULL, <i>file</i> must represent the full
location of the image that is to be decoded. If this file can not
be found or accessed
<p>
To fully appreciate this function, one is advised to read the
XmImageInfo(3X) manual page.
</blockquote>
<h3><font face="helvetica,arial">Return Value</font></h3>
<blockquote>
A newly allocated XmImageInfo structure or NULL upon failure.
<p>
Common causes for failure are:
<p>
<ul>
<li>the image to be decoded is of an unsupported type;
<li>the <i>file</i> argument is NULL;
<li>the <i>file</i> argument represents a file that could not be
found or accessed.
</ul>
</blockquote>
<h3><font face="helvetica,arial">Examples</font></h3>
<blockquote>
The simplest example of a function installed for the XmNimageProc resource
is the following:
<pre>
XmImageInfo*
loadImage(Widget w, String url, Dimension width, Dimension height,
XtPointer client_data)
{
return(XmHTMLImageDefaultProc(w, url, NULL, 0));
}
</pre>
A more advanced example is:
<pre>
XmImageInfo*
loadImage(Widget w, String url, Dimension width, Dimension height,
XtPointer client_data)
{
XmImageInfo *image_info;
unsigned char image_type = IMAGE_UNKNOWN;
/* check if this is a local url */
if((XmHTMLGetURLType(url)) != ANCHOR_FILE_LOCAL)
return(NULL);
/* it is a local file. Check if it is of a supported type */
image_type = XmHTMLImageGetType(url, NULL, 0);
if(image_type == IMAGE_ERROR || image_type == IMAGE_UNKNOWN)
{
/* an error occured or the type of this image is unsupported */
return(NULL);
}
/* Load it using the default function */
if((image_info = XmHTMLImageDefaultProc(w, url, NULL, 0)) != NULL)
{
/*
* Prevent a XmHTML widget from freeing this image immediatly.
* Also prevent scaling of the image (scaling images is
* actually a violation of the HTML standard!).
*/
image_info->options &= ~XmIMAGE_DEFERRED_FREE & ~XmIMAGE_ALLOW_SCALE;
return(image_info);
}
return(NULL);
}
</pre>
A more advanced version of this function could fetch remote images,
check if support for JPEG and PNG images is available before calling
XmHTMLImageDefaultProc, use delayed image loading, implement a caching
scheme for the returned XmImageInfo structure or add a decoder for image
types unsupported by XmHTMLImageDefaultProc (this can include other types
of animations as well!).
</blockquote>
<h3><font face="helvetica,arial">See Also</font></h3>
<blockquote>
XmHTML(3X), XmImageInfo(3X), XmImageCreate(3X), XmImageCreateFromInfo(3X),
XmImageDestroy(3X), XmImage(3X)
</blockquote>
<hr noshade size="2" width="25%">
<i><font size="-1">
XmHTML, June 4, 1998
</font></i>
</body>
</html>
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