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<HTML><HEAD><TITLE>Xlib Programming Manual: Window Attributes: Background</TITLE></HEAD><BODY><H1 ALIGN=center>3.2.1 Background Attribute</H1>Only<B><A HREF="../create.html#InputClass">InputOutput</A></B>windows can have a background.You can set the background of an<B><A HREF="../create.html#InputClass">InputOutput</A></B>window by using a pixel or a pixmap.<P>The background-pixmap attribute of a window specifies the pixmap to be used for a window's background.This pixmap can be of any size, although some sizes may be faster than others.The background-pixel attribute of a window specifies a pixel value used to painta window's background in a single color.<A NAME="ParentRelative"></A><P>You can set the background-pixmap to a pixmap, <B>None</B>(default), or <B>ParentRelative</B>.You can set the background-pixel of a window to any pixel value (no default).If you specify a background-pixel, it overrides either the default background-pixmapor any value you may have set in the background-pixmap.A pixmap of an undefined size that is filled with the background-pixel is used for the background.Range checking is not performed on the background pixel;it simply is truncated to the appropriate number of bits.<P>If you set the background-pixmap,it overrides the default.The background-pixmap and the window must have the same depth,or a<B>BadMatch</B>error results.If you set background-pixmap to<B>None</B>,the window has no defined background. If you set the background-pixmap to<B>ParentRelative</B>:<UL><P><LI>The parent window's background-pixmap is used. The child window, however, must have the same depth as its parent,or a<B>BadMatch</B>error results.<P><LI>If the parent window has a background-pixmap of<B>None</B>,the window also has a background-pixmap of<B>None</B>. <P><LI>A copy of the parent window's background-pixmap is not made.The parent's background-pixmap is examined each time the child window's background-pixmap is required. <P><LI>The background tile origin always aligns with the parent window'sbackground tile origin. If the background-pixmap is not<B>ParentRelative</B>,the background tile origin is the child window's origin.</UL><P>Setting a new background, whether by setting background-pixmap orbackground-pixel, overrides any previous background.The background-pixmap can be freed immediately if no further explicit referenceis made to it (the X server will keep a copy to use when needed).If you later draw into the pixmap used for the background,what happens is undefined because theX implementation is free to make a copy of the pixmap orto use the same pixmap.<P>When no valid contents are available for regions of a windowand either the regions are visible or the server is maintaining backing store,the server automatically tiles the regions with the window's backgroundunless the window has a background of<B>None</B>.If the background is<B>None</B>,the previous screen contents from other windows of the same depth as the windoware simply left in place as long as the contents come from the parent of thewindow or an inferior of the parent.Otherwise, the initial contents of the exposed regions are undefined.<B><A HREF="../../events/exposure/expose.html">Expose</A></B> events are then generated for the regions, even if the background-pixmapis<B>None</B>(see "<A HREF="../../events/exposure/">Exposure events</A>").<H5 ALIGN=right><I>Next: <A HREF="border.html">Border Attribute</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>?? 快捷鍵說明
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