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

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<H2><A NAME="sec:10.13"><SPAN class="sec-nr">10.13</SPAN> <SPAN class="sec-title">Printing 
from <font size=-1>XPCE</font> applications</SPAN></A></H2>

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

<P><A NAME="idx:printing:469"></A>You're wonderful application is 
finished ... but the users want
<B>printing???</B>. What to do? A computer screen is not a set of 
paper-sheets and therefore there is no trivial answer to this question. 
It depends on the nature of the data that needs to be printed, and also 
on the operating system used.

<P><A NAME="idx:PostScript:470"></A><B>In Unix</B> , printing is 
achieved by producing a document in a format that can be understood by 
the print-spooler program, normally either plain text or PostScript. If 
formatted text and/or included graphics are required it is often 
desirable to produce input for a formatting program, call the formatter 
and send the result to the printer.

<P><B>In Windows</B> the printer is not driven by a document, but using 
a series of calls on a GDI (Graphical Device Interface) representing the 
printer. The good news of this is that whatever you can get on the 
screen you easily get on the printer. The bad news has been explained 
above: paper is not the same as your screen. It has pages, is generally 
worse in colour-handling but provides a much higher resolution. The 
users do not expect a series of screendumps from your applications. Most 
Windows applications however are WYSIWYG and there are no established 
standards for formatting applications.

<H3><A NAME="sec:10.13.1"><SPAN class="sec-nr">10.13.1</SPAN> <SPAN class="sec-title">Options 
for document generation</SPAN></A></H3>

<P>Below is a brief overview of the options available.

<P>
<UL>
<LI><I>Generating PostScript</I><BR>
All <font size=-1>XPCE</font> <A class="" href="summary.html#class:graphical">graphical</A> 
objects support the method <B><CODE>&lt;-</CODE>postscript</B> that 
creates an Adobe PostScript representation of the object. For most 
objects used in diagrams (lines, curves, text), the produced PostScript 
is clean PostScript ready for perfect scaling. The remaining objects 
(for example a menu or button) are translated into an <A class="" href="summary.html#class:image">image</A> 
which is then translated to PostScript. Such objects scale poorly.

<P>This facility is useful for creating high-quality diagrams that can 
be imported in a text created on an external application. This is fairly 
portable, but using Microsoft applications you must have a PostScript 
printer attached and there is no previewing. On Windows platform there 
is no well-supported automated way to print a PostScript file unless you 
can asks your users to install a PostScript viewer such as
<A NAME="idx:AlladinGsView:471">Alladin GsView</A><A NAME="idx:gsview:472"></A>.

<P>
<LI><I>Generating plain text</I><BR>
If you need to produce a listing, you can generate a plain ISO-Latin-1 
(or other 8-bit character set) string and print this. On Unix this is 
achieved by sending the text to the printer-spooler. On Windows you can 
save the data to a temporary file and start the command <CODE>notepad /p 
"file"</CODE>. This route provides no support for graphics or any kind 
of advanced formatting.

<P>
<LI><I>Generating markup</I><BR>
Translating project data to output on a page is a craft that is 
understood by text-manipulation programs that accept a high-level input 
specification such as Troff, LaTeX or an SGML variant. If you can expect 
your users to have or install a particular package and this package can 
deal with PostScript graphics this is the ideal way to generate 
good-looking documents from your application. On Unix these tools are 
widely available and installed on most machines. Most of them are 
available on Windows, but not installed on most systms.

<P>The <CODE>library(http/html_write)</CODE> library described in <B>section 
??</B> provides a good infra-structure for emitting documents in HTML or 
another SGML or XML dialect. There is no such library for LaTeX , but 
this can be designed using the same principles.

<P>Using HTML, the application can be transformed into a web-server 
using the infrastructure described in <A class="sec" href="httpd.html">section 
11.9</A>. The user can use standard web-technologies to process the 
page. Unfortunately well-established web technology does not support 
vector-drawings, though the emerging <A NAME="idx:SVG:473">SVG</A> 
technology may change that.

<P>
<LI><I>Generating a Windows meta-file</I><BR>
<A NAME="idx:WMF:474"></A><A NAME="idx:EMF:475"></A>Windows metafiles 
are implemented in the class <B>win_metafile</B>, providing both input 
and output of metafiles. Such files preserve the vector properties of <font size=-1>XPCE</font> 
graphicals and can be imported in most native Windows applications. 
Unfortunately the scaling properties, especially of text, are much worse 
than PostScript.

<P>An example of exporting Windows Metafiles is in PceDraw in the file
<CODE>library(draw/canvas)</CODE>.

<P>
<LI><I>Printing to a Windows printer</I><BR>
Using class <B>win_printer</B>, the user can open a device on which 
graphicals can be painted and that can be advanced to the next page. 
This technique only works on Windows and requires you to program all 
details of the page. For WYSIWYG objects such as most drawings, this 
techinique is appropriate, but rendering textual documents require the 
implementation of a formatter, where you are responsible for page 
headers and footers, alignment, etc.

<P>Formatting text in sections, paragraphs lists, etc. is provided by 
the
<font size=-1>XPCE</font> document-rendering classes described in <A class="sec" href="docrender.html">section 
11.10</A>. These classes cannot handle pagination though. Another 
alternative is the use of <A class="" href="summary.html#class:editor">editor</A> 
and friends, drawing the <A class="" href="summary.html#class:text_image">text_image</A> 
on a page while traversing through the document.

<P>An example of printing using <B>win_printer</B> is in PceDraw in the 
file <CODE>library(draw/canvas)</CODE>.
</UL>

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