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<concept id="GUID-CE7CF024-4898-551A-841B-38EC57A3EC82" xml:lang="en"><title>Ordinal
Position</title><shortdesc>All windows in the Window Server have an <keyword>ordinal     
   position</keyword> which describes their z-order—that is, their ordering
from nearest the viewer to furthest away from the viewer. Each window’s ordinal
position is relative to its parent window and is unique among its siblings. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p> <b>Variant</b>: Both (ScreenPlay and non-ScreenPlay). <b>Target audience</b>:
Application developers. </p>
<p>Ordinal positions are positive integers starting at 0, with 0 being the
front-most position. A window with an ordinal position of 0 is displayed in
the <keyword>foreground</keyword>, i.e., in front of all its sibling windows.
The ordinal position of other windows increases by one for each position behind
this window. </p>
<p>When a window is created, it is automatically given an ordinal position
of 0 within its parent window. Then, when another child of the same parent
is created, the first window’s ordinal position changes to 1, and the new
window’s position is 0. These ordinal positions can be changed after the windows
have been created, using functions provided by the <codeph>RWindowTreeNode</codeph> class. </p>
<p>When a window's ordinal position is changed, its order in the sibling list
is also changed, so that the window with ordinal position 0 is always first
in the sibling list, the window with ordinal position 1 is next in the list,
and so on. Changing the ordinal position of windows therefore affects the
result of the <xref href="GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D.dita#GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D/GUID-12634A4D-36F1-35AD-8D61-EEA63872CF8B"><apiname>RWindowTreeNode::Parent()</apiname></xref>, <xref href="GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D.dita#GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D/GUID-1FFFFED4-5062-3C9D-B9A6-A89B107080FF"><apiname>RWindowTreeNode::Child()</apiname></xref>, <xref href="GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D.dita#GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D/GUID-F11A3640-844E-30D3-AAB2-D154E4EACBB4"><apiname>RWindowTreeNode::NextSibling()</apiname></xref> and <xref href="GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D.dita#GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D/GUID-1B6C1D5F-8F27-3472-87EE-CBB90D1A9280"><apiname>RWindowTreeNode::PrevSibling()</apiname></xref> functions. </p>
<p>To give an illustration of how ordinal positions work, the diagram below
shows three windows, A, B and C, all belonging to the same window group. Their
ordinal positions are as follows: A=0; B=1; C=2. </p>
<fig id="GUID-FB15A25F-FB7A-5031-9D17-51CD7C8ACA1D">
<image href="GUID-694C7416-927E-58F7-B010-CA55D2FFA88F_d0e189143_href.png" placement="inline"/>
</fig>
<p>This would be the default ordering of the windows if they were created
in the order CBA. Many sibling windows within an application may not overlap
in practice: nevertheless, each window has a unique ordinal position, even
though this will not be evident in the way they are displayed. </p>
<p>If a window’s ordinal position is changed, its position on the screen will
change. All its child windows also move with it, although their ordinal positions,
which are relative to the parent, don’t change. </p>
<section id="GUID-4B42408E-06DC-4A98-9AC8-7EEAF533D614"><title>Moving a window to the front</title> <p>A window is moved
to the front (i.e., to the <keyword>foreground</keyword>) by giving it an
ordinal position of 0. The diagram below shows windows A, B and C, but window
B has now been given an ordinal position of 0. A’s position has been incremented
to 1, and C’s remains as 2. </p> <fig id="GUID-0B1ED6C1-4F47-5527-A9F9-5B4AD03528D5">
<image href="GUID-74B329CD-4640-5636-9D8D-20F0D7E09EB4_d0e189164_href.png" placement="inline"/>
</fig> <p>The diagram below shows the same three windows as above, except
that window B now contains a child window, D. Window D’s ordinal position
is 0, relative to its parent window, B. </p> <fig id="GUID-313C9AEE-6ADB-5842-9EB6-0D563D7FC582">
<image href="GUID-7AE4D17F-728A-5B7E-A3F9-A903E64731B1_d0e189172_href.png" placement="inline"/>
</fig> <p>If window A is now moved to the front, window B moves behind it,
as shown in the diagram below. Window D’s ordinal position is still 0, but
because its position is relative to its parent window, it moves with window
B to behind window A. </p> <fig id="GUID-B6882EE3-C071-522B-9D7E-86D84F8D64DC">
<image href="GUID-40A3938E-366E-5318-A7FA-146F9E5E23B1_d0e189180_href.png" placement="inline"/>
</fig> </section>
<section id="GUID-EDA73282-0AB9-49EE-BAAB-C6D0DB267F56"><title>Moving a window to the back</title> <p>If a window is given
an ordinal position greater than all its siblings, it is moved to the back
of them. For convenience, the functions for setting ordinal position allow
a negative ordinal position to be specified, which sends the window to the
back and sets its ordinal position to be the highest among its siblings. </p> </section>
<section id="GUID-5288AAAA-9513-4981-98E1-8B5F4EDAC35C"><title>Ordinal position of window groups</title> <p>The ordinal position
of a window group has special significance because there is normally one window
group per application. As a result, the z-order of applications on the screen
is typically determined by the ordinal positions of their window groups. For
example, giving a window group an ordinal position of 0 typically brings an
application to the front of the screen. Note, however, that window groups
also have a priority, which overrides ordinal position. Ordinal position only
applies among window groups of the same priority. </p> <p>The ordinal position
of window groups is typically controlled by a shell or similar application.
The <xref href="GUID-643DDA78-C7A7-386D-AB3F-8710141DDDA9.dita"><apiname>RWsSession</apiname></xref> class provides functions for
such applications to set window group ordinal positions. </p> </section>
<section id="GUID-D5CA8ED0-CD91-4FB9-B56F-613EE825435C"><title>Keyboard focus and window group ordinal position</title> <p>When
a window group is given an ordinal position of 0, it is automatically given
keyboard focus, unless it has disabled keyboard focus by calling <codeph>EnableReceiptOfFocus(EFalse)</codeph>,
or another window group has a higher priority. </p> </section>
</conbody><related-links>
<link href="GUID-99AE1D62-571A-5A63-B472-C0FBC0861F52.dita"><linktext>Window Types</linktext>
</link>
</related-links></concept>