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<HTML><HEAD><TITLE>Xlib Programming Manual: GraphicsExpose and NoExpose Events</TITLE></HEAD><BODY><H1 ALIGN=center>10.9.2 GraphicsExpose and NoExpose Events</H1><!.IN "Events" "GraphicsExpose"><!.IN "Events" "NoExpose"><!.IN "GraphicsExpose" "" "@DEF@">The X server can report<B>GraphicsExpose</B>events to clients wanting information about when a destination region could notbe computed during certain graphics requests:<B><A HREF="../../graphics/XCopyArea.html">XCopyArea()</A></B>or<B><A HREF="../../graphics/XCopyPlane.html">XCopyPlane()</A></B>.The X server generates this event whenever a destination region could not becomputed due to an obscured or out-of-bounds source region.In addition, the X server guarantees to report contiguously all of the regions exposed bysome graphics request (for example, copying an area of a drawable to a destinationdrawable).<P><!.IN "NoExpose" "" "@DEF@">The X server generates a<B>NoExpose</B>event whenever a graphics request that mightproduce a<B>GraphicsExpose</B>event does not produce any.In other words, the client is really asking for a<B>GraphicsExpose</B>event but instead receives a<B>NoExpose</B>event.<P>To receive<B>GraphicsExpose</B>or<B>NoExpose</B>events, you must first set the graphics-exposure attribute of the graphics context to<B>True</B>.You also can set the graphics-expose attribute when creating a graphicscontext using<B><A HREF="../../GC/XCreateGC.html">XCreateGC()</A></B>or by calling<B><A HREF="../../GC/convenience-functions/XSetGraphicsExposures.html">XSetGraphicsExposures()</A></B>.<P>The structures for these event types contain:<A NAME="XGraphicsExposeEvent"></A><P><!.IN "XGraphicsExposeEvent" "" "@DEF@"><CODE><PRE>typedef struct { int type; /* GraphicsExpose */ 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 */ Display *display; /* Display the event was read from */ Drawable drawable; int x, y; int width, height; int count; /* if nonzero, at least this many more */ int major_code; /* core is CopyArea or CopyPlane */ int minor_code; /* not defined in the core */} XGraphicsExposeEvent;</PRE></CODE><A NAME="XNoExposeEvent"></A><P><!.IN "XNoExposeEvent" "" "@DEF@"><CODE><PRE>typedef struct { int type; /* NoExpose */ 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 */ Display *display; /* Display the event was read from */ Drawable drawable; int major_code; /* core is CopyArea or CopyPlane */ int minor_code; /* not defined in the core */} XNoExposeEvent;</PRE></CODE><P>Both structures have these common members: drawable, major_code, and minor_code.The drawable member is set to the drawable of the destination region on which the graphics request was to be performed.The major_code member is set to the graphics request initiated by the clientand can be either<B>X_CopyArea</B>or<B>X_CopyPlane</B>.If it is<B>X_CopyArea</B>,a call to<B><A HREF="../../graphics/XCopyArea.html">XCopyArea()</A></B>initiated the request.If it is<B>X_CopyPlane</B>,a call to<B><A HREF="../../graphics/XCopyPlane.html">XCopyPlane()</A></B>initiated the request.These constants are defined in <B><TT><X11/Xproto.h></TT></B>.The minor_code member,like the major_code member, indicates which graphics request was initiated bythe client. However, the minor_code member is not defined by the coreX protocol and will be zero in these cases, although it may be used by an extension.<P>The <B>XGraphicsExposeEvent</B>structure has these additional members: x, y, width, height, and count. The x and y members are set to the coordinates relative to the drawable's originand indicate the upper-left corner of the rectangle.The width and height members are set to the size (extent) of the rectangle.The count member is set to the number of<B>GraphicsExpose</B>events to follow.If count is zero, no more<B>GraphicsExpose</B>events follow for this window.However, if count is nonzero, at least that number of<B>GraphicsExpose</B>events (and possibly more) are to follow for this window.<H5 ALIGN=right><I>Next: <A HREF="../window-state-change/">Window State Change 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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