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<HTML><HEAD><TITLE>Xlib Programming Manual: Expose Events</TITLE></HEAD><BODY><H1 ALIGN=center>10.9.1 Expose Events </H1><!.IN "Events" "Expose"><!.IN "Expose" "" "@DEF@">The X server can report<B>Expose</B>events to clients wanting information about when the contents of window regionshave been lost.The circumstances in which the X server generates<B>Expose</B>events are not as definite as those for other events.However, the X server never generates<B>Expose</B>events on windows whose class you specified as<B><A HREF="../../window/create.html#InputClass">InputOnly</A></B> .The X server can generate<B>Expose</B>events when no valid contents are available for regions of a windowand either the regions are visible, the regions are viewable and the server is (perhaps newly) maintaining backing store on the window,or the window is not viewable but the server is (perhaps newly) honoring thewindow's <A HREF="../../window/attributes/backing-store.html">backing-store</A> attribute of<B>Always</B>or<B>WhenMapped</B>.The regions decompose into an (arbitrary) set of rectangles,and an<B>Expose</B>event is generated for each rectangle.For any given window,the X server guarantees to report contiguously all of the regions exposed by some action that causes <B>Expose</B>events, such as raising a window.<P>To receive<B>Expose</B>events, set the<B>ExposureMask</B>bit in the <A HREF="../../window/attributes/event-and-do-not-propagate.html">event-mask</A> attribute of the window. <A NAME="XExposeEvent"></A><P>The structure for this event type contains:<P><!.IN "XExposeEvent" "" "@DEF@"><CODE><PRE>typedef struct { int type; /* Expose */ unsigned long serial; /* # of last request processed by server */ Bool send_event; /* true if this came from a <B><A HREF="../../appendix/a.html#SendEvent">SendEvent</A></B> request */ <A HREF="../../display/opening.html#Display">Display</A> *display; /* Display the event was read from */ Window window; int x, y; int width, height; int count; /* if nonzero, at least this many more */} XExposeEvent;</PRE></CODE><P>The <B>window</B> member is set to the exposed (damaged) window.<P>The <B>x</B> and <B>y</B> members are set to the coordinates relative to the window's originand indicate the upper-left corner of the rectangle.<P>The <B>width</B> and <B>height</B> members are set to the size (extent) of the rectangle.<P>The <B>count</B> member is set to the number of<B>Expose</B>events that are to follow.If <B>count</B> is zero, no more<B>Expose</B>events follow for this window.However, if <B>count</B> is nonzero, at least that number of <B>Expose</B>events (and possibly more) follow for this window.Simple applications that do not want to optimize redisplay by distinguishingbetween subareas of its window can just ignore all<B>Expose</B>events with nonzero counts and perform full redisplayson events with zero counts.<H5 ALIGN=right><I>Next: <A HREF="graphics-expose-and-no-expose.html">GraphicsExpose and NoExpose Events</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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