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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_d0e236264_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_d0e236285_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_d0e236293_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_d0e236301_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>