/usr/share/doc/swi-prolog-doc/UserGuide/resources.html

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<H1><A NAME="sec:9"><SPAN class="sec-nr">9</SPAN> <SPAN class="sec-title">Program 
resources</SPAN></A></H1>

<A NAME="sec:resources"></A>

<P>Resources, in the new sense of the word is data that is required by 
an application but cannot be expressed easily as program-code. Examples 
are image-files, help-files, and other files using non-Prolog syntax. 
Such files are declared by defining clauses for the predicate
<A NAME="idx:resource3:273"></A><A class="pred" href="resources.html#resource/3">resource/3</A>:

<DL>
<DT class="pubdef"><A NAME="resource/3"><STRONG>resource</STRONG>(<VAR>?Name, 
?Class, ?PathSpec</VAR>)</A></DT>
<DD class="defbody">
Define the file specified by <VAR>PathSpec</VAR> to contain data for the 
resource named <VAR>Name</VAR> of resource-class <VAR>Class</VAR>.

<P><VAR>Name</VAR> refers to the logical name of the resource, which is 
interpreted locally for a Prolog module. Declarations in the module
<CODE>user</CODE> are visible as defaults from all other modules.
<VAR>Class</VAR> defines the type of object to be expected in the file. 
Right now, they provide an additional name-space for resources. <VAR>PathSpec</VAR> 
is a file specification as acceptable to <A NAME="idx:absolutefilename23:274"></A><SPAN class="pred-ext">absolute_file_name/[2,3]</SPAN>.
</DD>
</DL>

<P>Resources can be handled both from Prolog as for <font size=-1>XPCE</font>. 
From Prolog, this is achieved using <A NAME="idx:openresource3:275"></A><SPAN class="pred-ext">open_resource/3</SPAN>:

<DL>
<DT class="pubdef"><A NAME="open_resource/4"><STRONG>open_resource</STRONG>(<VAR>+Name, 
?Class, -Stream</VAR>)</A></DT>
<DD class="defbody">
Opens the resource specified by <VAR>Name</VAR> and <VAR>Class</VAR>. If 
the latter is a variable, it will be unified to the class of the first 
resource found that has the specified <VAR>Name</VAR>. If successful,
<VAR>Stream</VAR> becomes a handle to a binary input stream, providing 
access to the content of the resource.

<P>The predicate <A NAME="idx:openresource3:276"></A><SPAN class="pred-ext">open_resource/3</SPAN> 
first checks <A NAME="idx:resource3:277"></A><A class="pred" href="resources.html#resource/3">resource/3</A>. 
If successful it will open the returned resource source-file. Otherwise 
it will look in the programs resource database. When creating a 
saved-state, the system saves the resource contents into the resource 
archive, but does not save the resource clauses.

<P>This way, the development environment uses the files (and 
modifications to the <A NAME="idx:resource3:278"></A><A class="pred" href="resources.html#resource/3">resource/3</A> 
declarations and/or files containing resource info thus immediately 
affect the running environment, while the runtime system quickly 
accesses the system resources.
</DD>
</DL>

<P>From <font size=-1>XPCE</font>, resources are accessed using the 
class
<A class="" href="summary.html#class:resource">resource</A>, which is 
located next to <A class="" href="summary.html#class:file">file</A> 
below the common data-representation class <A class="" href="summary.html#class:source_sink">source_sink</A>. 
Many of the methods that require data accept instances of <A class="" href="summary.html#class:source_sink">source_sink</A>, 
making resources a suitable candidate.

<P>Below is the preferred way to specify and use an icon.

<PRE class="code">
resource(my_icon,       image,  image('my_icon.xpm')).

        ...,
        send(Button, label, image(resource(my_icon))),
        ...,

</PRE>

<P>The directive <A NAME="idx:pceimagedirectory1:279"></A><SPAN class="pred-ext">pce_image_directory/1</SPAN> 
adds the provided directory to the search-path for images (represented 
in the class-variable
<B><CODE>image.path</CODE></B>), as well as to the image/1 definition of <A NAME="idx:filesearchpath2:280"></A><SPAN class="pred-ext">file_search_path/2</SPAN>.

<P>Please note that MS-Windows formatted image files can currently not 
be loaded through <A class="" href="summary.html#class:resource">resource</A> 
objects. The Windows API only provides functions to extract these 
objects from a single file, or nested as Windows resources in a <CODE>.dll</CODE> 
or <CODE>.exe</CODE> file.

<P>Right now, it is advised to translate the images into <CODE>.xpm</CODE> 
format using the following simple command:

<PRE class="code">
?- send(image('myicon.ico'), save, 'myicon,xpm', xpm).
</PRE>

<P>This transformation is complete as the <CODE>.XPM</CODE> image format 
covers all aspects of the Microsoft image formats. For further details 
on image formats and manipulation, see <A class="sec" href="images.html">section 
10.10</A>.
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