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<HTML><HEAD><TITLE>Xlib Programming Manual: Window Attributes: Gravity</TITLE></HEAD><BODY><H1 ALIGN=center>3.2.3 Gravity Attributes</H1>The bit gravity of a window defines which region of the window should be retained when an<B><A HREF="../create.html#InputClass">InputOutput</A></B>window is resized. The default value for the bit-gravity attribute is <B>ForgetGravity</B>.The window gravity of a window allows you to define how the <B><A HREF="../create.html#InputClass">InputOutput</A></B>or<B><A HREF="../create.html#InputClass">InputOnly</A></B>window should be repositioned if its parent is resized. The default value for thewin-gravity attribute is <B>NorthWestGravity</B> .<P>If the inside height of a window is not changed and if the window is moved or its border is changed, then the contents of the window are not lost but move with the window.Changing the inside width orheight of the window causes its contents to bemoved or lost (depending on the bit-gravity of the window) and causeschildren to be reconfigured (depending on their win-gravity).For achange of width and height, the (x, y) pairs are defined:<P><TABLE><TR><TD COLSPAN=2><HR><TR><TH>Gravity Direction <TH>Coordinates<TR><TD COLSPAN=2><HR><TR><TD><B>NorthWestGravity</B> <TD>(0, 0)<TR><TD><B>NorthGravity</B> <TD>(Width/2, 0)<TR><TD><B>NorthEastGravity</B> <TD>(Width, 0)<TR><TD><B>WestGravity</B> <TD>(0, Height/2)<TR><TD><B>CenterGravity</B> <TD>(Width/2, Height/2)<TR><TD><B>EastGravity</B> <TD>(Width, Height/2)<TR><TD><B>SouthWestGravity</B> <TD>(0, Height)<TR><TD><B>SouthGravity</B> <TD>(Width/2, Height)<TR><TD><B>SouthEastGravity</B> <TD>(Width, Height)</TABLE><P>When a window with one of these bit-gravity values is resized, the corresponding pairdefines the change in position of each pixel in the window.When a window with one of these win-gravities has its parent window resized,the corresponding pair defines the change in position of the window within the parent.When a window is so repositioned, a<B><A HREF="../../events/window-state-change/gravity.html">GravityNotify</A></B>event is generated.<P>A bit-gravity of<B>StaticGravity</B> indicates that the contents or origin should not move relative to the origin of the root window.If the change in size of the window is coupled with a change in position (x, y),then for bit-gravity the change in position of each pixel is (-x, -y), and forwin-gravity the change in position of a child when its parent is so resized is(-x, -y).Note that<B>StaticGravity</B>still only takes effect when the width or height of the window is changed, not when the window is moved.<P>A bit-gravity of <B>ForgetGravity</B> indicates that the window's contents are always discarded after a size change, even if a backing store or save under has been requested.The window is tiled with its <A HREF="background.html">background</A>and zero or more <B><A HREF="../../events/exposure/expose.html">Expose</A></B> events are generated. If no <A HREF="background.html">background</A> is defined, the existing screen contents are notaltered.Some X servers may also ignore the specified bit-gravity and always generate <B><A HREF="../../events/exposure/expose.html">Expose</A></B>events.<P>The contents and borders of inferiors are not affected by their parent'sbit-gravity.A server is permitted to ignore the specified bit-gravity and use<B>Forget</B>instead.<P>A win-gravity of <B>UnmapGravity</B> is like <B>NorthWestGravity</B>(the window is not moved),except the child is alsounmapped when the parent is resized,and an <B><A HREF="../../events/window-state-change/unmap.html">UnmapNotify</A></B> event isgenerated.<H5 ALIGN=right><I>Next: <A HREF="backing-store.html">Backing Store 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>⌨️ 快捷键说明
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