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

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<H2><A NAME="sec:5.3"><SPAN class="sec-nr">5.3</SPAN> <SPAN class="sec-title">Connecting 
graphical objects</SPAN></A></H2>

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

<P><A NAME="idx:graph:177"></A>The primary application domain of <font size=-1>XPCE</font> 
is handling graphical modelling languages. Drawing in such languages 
often entails connecting graphical objects using lines. Instead of 
adding an instance of <A class="" href="summary.html#class:line">line</A> 
to the graphical device at the proper place, it is much better to 
declare two graphical objects to be connected. Class <A class="" href="summary.html#class:connection">connection</A> 
provides for this.

<P>To prepare an object for making connections, the object should first 
define <A class="" href="summary.html#class:handle">handles</A>. Below 
is a simple example. The link is a <EM>reusable</EM> object and 
therefore defined as a global reference. See <A class="sec" href="namedref.html">section 
10.3</A>. The screendump is shown in <A class="fig" href="connection.html#fig:connect">figure 
13</A>.

<PRE class="code">
:- pce_global(@in_out_link, make_in_out_link).

make_in_out_link(L) :-
        new(L, link(in, out, line(arrows := second))).

linked_box_demo :-
        new(P, picture('Linked Box demo')),
        send(P, open),
        send(P, display, new(B1, box(50,50)), point(20,20)),
        send(P, display, new(B2, box(25,25)), point(100,100)),
        send(B1, handle, handle(w, h/2, in)),
        send(B2, handle, handle(w/2, 0, out)),
        send_list([B1, B2], recogniser, new(move_gesture)),
        send(B1, connect, B2, @in_out_link).</PRE>

<P><A NAME="fig:connect"></A>
<CENTER>
<IMG SRC="connect.gif">
</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Figure 13 : </B>A connection between two boxes</TABLE>

<P>If there are multiple handles of the same `kind' on a graphical, a 
connection will automatically try to connect to the `best' handle.

<P>The classes related to making connections are summarised in
<A class="tab" href="connection.html#tab:connectclasses">table 4</A>.

<P>
<CENTER>
<TABLE BORDER=2 FRAME=box RULES=groups>
<TR VALIGN=top><TD><A class="" href="summary.html#class:connection">connection</A> </TD><TD>Subclass 
of class <A class="" href="summary.html#class:line">line</A>. A 
connection can connect two graphicals on the same window that have 
handles. The line is automatically updated if either of the graphicals 
is moved, resized, changed from device, (un)displayed, hidden/exposed or 
destroyed. </TD></TR>
<TBODY>
<TR VALIGN=top><TD><A class="" href="summary.html#class:handle">handle</A> </TD><TD>Defines 
the location, nature and name of a connection point for a connection. 
Handles can be attached to individual graphicals as well as to their 
class. </TD></TR>
<TBODY>
<TR VALIGN=top><TD><A class="" href="summary.html#class:link">link</A> </TD><TD>Defines 
the generic properties of a connection: the nature (`kind') of the 
handle at either side and the line attributes (arrows, pen and colour). </TD></TR>
<TBODY>
<TR VALIGN=top><TD><A class="" href="summary.html#class:connect_gesture">connect_gesture</A> </TD><TD>Event-processing 
object (see <A class="sec" href="recogniser.html">section 5.5</A>) used 
to connect two graphical objects. </TD></TR>
</TABLE>

</CENTER>
<TABLE ALIGN=center WIDTH="75%"><TR><TD>
<B>Table 4 : </B>Classes used to define connections</TABLE>

<A NAME="tab:connectclasses"></A>

<P>Note that, as class <A class="" href="summary.html#class:connection">connection</A> 
is a subclass of
<A class="" href="summary.html#class:graphical">graphical</A>, 
connections can be created between connections. Class
<A class="" href="summary.html#class:graphical">graphical</A> defines 
various methods to help reading the relations expressed with connections 
and/or refine the generic
<A class="" href="summary.html#class:connect_gesture">connect_gesture</A>.

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swi-prolog-doc 5.6.59-2 / usr / share / doc / swi-prolog-doc / UserGuide / connection.html
