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<HTML><HEAD><TITLE>Xlib Programming Manual: Extensions: Hooks into the Library</TITLE></HEAD><BODY><H1 ALIGN=center>Hooks into the Library</H1>These functions allow you to define procedures that are to becalled when various circumstances occur.The procedures include the creation of a new GC for a connection,the copying of a GC, the freeing of a GC, the creating and freeing of fonts,the conversion of events defined by extensions to and from wireformat, and the handling of errors.<P>All of these functions return the previous procedure defined for thisextension.<P>To define a procedure to be called whenever<B><A HREF="../../display/XCloseDisplay.html">XCloseDisplay()</A></B>is called, use<B><A HREF="XESetCloseDisplay.html">XESetCloseDisplay()</A></B>.<P>To define a procedure to be called whenever a new <A HREF="../../GC/manipulating.html">GC</A> is created, use<B><A HREF="XESetCreateGC.html">XESetCreateGC()</A></B>.<P>To define a procedure to be called whenever a <A HREF="../../GC/manipulating.html">GC</A> is copied, use<B><A HREF="XESetCopyGC.html">XESetCopyGC()</A></B>.<P>To define a procedure to be called whenever a <A HREF="../../GC/manipulating.html">GC</A> is freed, use<B><A HREF="XESetFreeGC.html">XESetFreeGC()</A></B>.<P>To define a procedure to be called whenever<B><A HREF="../../graphics/font-metrics/XLoadQueryFont.html">XLoadQueryFont()</A></B>and<B><A HREF="../../graphics/font-metrics/XQueryFont.html">XQueryFont()</A></B>are called, use<B><A HREF="XESetCreateFont.html">XESetCreateFont()</A></B>.<P>To define a procedure to be called whenever a font is freed, use<B><A HREF="XESetFreeFont.html">XESetFreeFont()</A></B>.<A NAME="xEvent"></A><P>The <B><A HREF="XESetWireToEvent.html">XESetWireToEvent()</A></B>and<B><A HREF="XESetEventToWire.html">XESetEventToWire()</A></B>functions allow you to define new events to the library.An <A HREF="../../events/structures.html#XEvent">XEvent</A>structure always has a type code (type<B>int</B>)as the first component.This uniquely identifies what kind of event it is.The second component is always the serial number (type<B>unsigned</B><B>long</B>)of the last request processed by the server.The third component is always a Boolean (type<B>Bool</B>)indicating whether the event came from a<B><A HREF="../a.html#SendEvent">SendEvent</A></B>protocol request.The fourth component is always a pointer to the displaythe event was read from.The fifth component is always a resource ID of one kind or another,usually a window, carefully selected to be useful to toolkit dispatchers.The fifth component should always exist, even ifthe event does not have a natural destination;if there is no valuefrom the protocol to put in this component, initialize it to zero.<P ALIGN=center><B>Note</B><BLOCKQUOTE>There is an implementation limit such that your host eventstructure size cannot be bigger than the size of the<A HREF="../../events/structures.html#XEvent">XEvent</A> union of structures.There also is no way to guarantee that more than 24 elements or 96 charactersin the structure will be fully portable between machines.</BLOCKQUOTE><P>To initialize the serial number component of the event, call<B><A HREF="_XSetLastRequestRead.html">_XSetLastRequestRead()</A></B>with the event and use the return value.<P>To define a procedure to be called whenever an extension error needs to beconverted from wire format to host format, use<B><A HREF="XESetWireToError.html">XESetWireToError()</A></B>.<P>To install an error procedure, use<B><A HREF="XESetError.html">XESetError()</A></B>.<P>To define a procedure to be called to define an error message, use<B><A HREF="XESetErrorString.html">XESetErrorString()</A></B>.<P>To define a procedure to be called when an extension error is printed, to print the error value, use<B><A HREF="XESetPrintErrorValues.html">XESetPrintErrorValues()</A></B>.<P>To define a procedure to be called whenever a <A HREF="../../GC/manipulating.html">GC</A> cacheneeds to be updated in the server, use<B><A HREF="XESetFlushGC.html">XESetFlushGC()</A></B>.<P>To define a procedure to be called whenever data is about to be sentto the server, use<B><A HREF="XESetBeforeFlush.html">XESetBeforeFlush()</A></B>.<H5 ALIGN=right><I>Next: <A HREF="hooks-onto-xlib-data-structures.html">Hooks onto Xlib Data Structures</A></I></H5><HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:ch.tronche@computer.org">ch.tronche@computer.org</A></ADDRESS></BODY></HTML>⌨️ 快捷键说明
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