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<concept id="GUID-0A13A931-016C-5325-97AF-2DE0B210DF2F" xml:lang="en"><title>Window
Server Client-Side Library Overview</title><shortdesc>The Window Server keeps track of window sizes, positions, visibility
and validity (keeping window content up to date). It also receives and distributes
user input in the form of key presses and pointer events. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Note that much of the Window Server API is low-level and is encapsulated
in the UI Control Framework API. </p>
<section id="GUID-E1891417-0C8F-46FE-BC4D-23C1E1BB750E"><title>Window Server client-side library details</title> <p>The following
table shows the DLLs that provides the functionality and the library to which
your code must link. </p> <table id="GUID-D5750916-4A95-5944-9ADB-05E35D47592B">
<tgroup cols="3"><colspec colname="col0"/><colspec colname="col1"/><colspec colname="col2"/>
<thead>
<row>
<entry>DLL</entry>
<entry>LIB</entry>
<entry>Short description</entry>
</row>
</thead>
<tbody>
<row>
<entry><p> <filepath>ws32_nga.dll</filepath>  </p> </entry>
<entry><p> <filepath>ws32.lib</filepath>  </p> </entry>
<entry><p>The Window Server client-side library for the <xref href="GUID-D93978BE-11A3-5CE3-B110-1DEAA5AD566C.dita">ScreenPlay</xref> variant. </p> </entry>
</row>
<row>
<entry><p> <filepath>ws32_nonnga.dll</filepath>  </p> </entry>
<entry> <p> <filepath>ws32.lib</filepath>  </p></entry>
<entry><p>The Window Server client-side library for the <xref href="GUID-F64E6551-670E-5E12-8103-DE504D3EC94F.dita">non-ScreenPlay</xref> variant. </p></entry>
</row>
</tbody>
</tgroup>
</table> <p>The details of the client-side API are very similar in the two
variants. There are some additional features in the ScreenPlay variant for
displaying surfaces.</p> </section>
<section id="GUID-D5B8436F-D7AA-4A72-A967-FC2BB8D8EB0B"><title>Architecture</title> <p>The Window Server is used by all applications
that have a user interface. The primary user input for these applications
comes from the keyboard and pointer, and their primary user-visible output
is to the screen. These input and output devices are shared between all applications
on the system. Each client thread opens a session to the server, and issues
requests for service. </p> <fig id="GUID-4EEE0DBF-A4DC-59A1-8310-504BF05204C7">
<title>              Window Server            </title>
<desc><p>The Window Server controls access by many client applications, to
the machine’s screen, keyboard and pointer. </p> </desc>
<image href="GUID-FE4BBEB4-4E5A-5BF2-A72F-AF53BAD83518_d0e164328_href.png" placement="inline"/>
</fig> <p>The Window Server thread runs at a higher priority than any application;
only the kernel runs at a higher priority. Therefore, all applications' requests
for screen updates, and all handling of machine events such as pointers and
keys, are handled at higher priority than any individual application. </p> <p>Each
client application runs in its own thread. The Window Server presents an interface
to client applications such that they can run without direct interaction with
the other applications on the machine. Drawing is clipped to the visible area
of the application’s windows. Pointer events are only received if they are
related to the application’s windows. Similarly, keyboard events are only
given to an application whose window group has focus or to one that has captured
them. A client application may ignore the majority of events relating to other
applications. It won't even be told about most of them. </p> <p>Each client
application communicates with the Window Server using a Window Server session,
or other object created from the session. The application waits to receive
events by setting up one or more active objects. Events include user input
and requests that windows be redrawn. Applications may create systems of windows
and draw to them. </p> </section>
<section id="GUID-A8BCF1C1-A637-4DDC-9249-BCEF4E23BA06"><title>Window server client-side API</title> <p>The following diagram
shows the key classes in the Window Server client-side library. Below the
diagram we provide a summary of the key concepts. </p> <fig id="GUID-A84A2706-1AF0-598B-976E-0980AD69E6E7">
<title>             Window Server client-side API classes            </title>
<image href="GUID-FEFF353E-DE8A-5FBA-B696-CD01D06BE813_d0e164353_href.png" placement="inline"/>
</fig> <table id="GUID-37EDAB58-6F7B-526A-8E46-891598924120">
<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>
<thead>
<row>
<entry>Concept</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><p> <b>Session</b>  </p> </entry>
<entry><p>A Window Server session allows an application to control and interrogate
its windows, the events it wishes to receive, and all other window groups
connected to the Window Server. A session is encapsulated by <xref href="GUID-643DDA78-C7A7-386D-AB3F-8710141DDDA9.dita"><apiname>RWsSession</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Events</b>  </p> </entry>
<entry><p>Applications function by waiting for events and handling them. Common
events are user input, and requests that windows be redrawn. The Window Server
session is used to request and obtain events. Most events (such as key and
point events) are encapsulated in <xref href="GUID-5D0B1595-1AC7-3C44-AC6B-0EFB5EABCF31.dita"><apiname>TWsEvent</apiname></xref>. </p> <p>A redraw
event tells the application what screen area needs redrawing. It is encapsulated
in <xref href="GUID-B5F16BF3-569D-3985-AAB7-439E3410468D.dita"><apiname>TWsRedrawEvent</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Window group</b>  </p> </entry>
<entry><p>A window group is special non-displayable type of window, which
can be considered as the root window of an application. Keyboard events and
focus are associated with it, and it can have a name, used for such things
as lists of running applications. A window group is provided by <xref href="GUID-64D4D428-D65F-3D9D-A0D4-C8338C848B25.dita"><apiname>RWindowGroup</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Drawable windows</b>  </p> </entry>
<entry><p>Drawable windows allow applications to draw to the screen. They
have operations to control size, position, visibility, scrolling, z-order,
and parent/child relationships. In a standard drawable window, areas that
become invalid (e.g. when an overlaying window is removed) must be redrawn
by the client application. It is provided by <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>. </p> <p>A
backed-up drawable window's content is stored by the Window Server, and redrawn
by the server when it becomes invalid. It is provided by <xref href="GUID-27A95595-F74D-32B2-A960-0CA290C8A3B3.dita"><apiname>RBackedUpWindow</apiname></xref>. </p> <p>These
window types are derived from a sequence of base classes, <xref href="GUID-9FFD28C7-8747-3438-84BF-44AF26ACEC7D.dita"><apiname>RWindowTreeNode</apiname></xref>, <xref href="GUID-1460DD8F-9AA1-3B99-8FFD-F309959CCA34.dita"><apiname>RWindowBase</apiname></xref>,
and <xref href="GUID-FDF4BB7E-8750-3564-982A-0124A977C82E.dita"><apiname>RDrawableWindow</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Graphics</b>  </p> </entry>
<entry><p>Applications draw to drawable windows through a windows graphics
context provided by a windows graphics device. These implement the abstract
graphics context and graphics device interfaces respectively, as defined in
the Graphics API. </p> <p>The windows graphics context is provided by <xref href="GUID-0AEE5955-C530-35F1-A904-69183331B294.dita"><apiname>CWindowGc</apiname></xref>;
the windows graphics device by <xref href="GUID-30479BE3-296E-3B4D-914D-B080ABD733E4.dita"><apiname>CWsScreenDevice</apiname></xref>. The bitmap
class, <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref>, is extended for most efficient use with
the Window Server by <xref href="GUID-17150D76-BB82-3A4B-8B1A-8BA93CB1A9EF.dita"><apiname>CWsBitmap</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Sprites and cursors</b>  </p> </entry>
<entry><p>A sprite is an arbitrary-shaped bitmap that can be moved without
applications having to redraw the underlying screen. It has one or more sprite
members, each containing a bitmap image and a time interval for that bitmap
to be displayed. The sprite class is <xref href="GUID-75C09150-E93B-323D-AFBF-E42C7BD78229.dita"><apiname>RWsSprite</apiname></xref>; the sprite
member class is <xref href="GUID-7F4E749E-D08D-3771-A3F1-9AEC5D16B78C.dita"><apiname>TSpriteMember</apiname></xref>. </p> <p>A specialized sprite
type is provided for pointer cursors, which automatically track the position
of a pointer. It is provided by <xref href="GUID-6E71A7F9-E980-3D99-ACB0-6743A0D13EBF.dita"><apiname>RWsPointerCursor</apiname></xref>. </p> <p>Text
cursors are handled by the class <xref href="GUID-CF377A98-F11F-380F-AD10-7F3E261D4421.dita"><apiname>CTextView</apiname></xref>. They can take
the form of a text or a line cursor. </p> </entry>
</row>
<row>
<entry><p> <b>Animation client</b>  </p> </entry>
<entry><p>Third-parties can write Window Server plug-in DLLs, as defined in
the Animation API, that perform animations. Providers of such animation DLLs
must also provide a client-side interface to allow applications to control
the animation. The base class for an animation client-side interface is <xref href="GUID-4180CDBA-E9A5-3A4B-9778-26D172FAFD10.dita"><apiname>RAnim</apiname></xref>. </p> <p>Clients
must request an animation DLL to be loaded before the animations provided
by it can be used. This is done through <xref href="GUID-800B3667-F45F-391F-A8A9-F876FB4ABC34.dita"><apiname>RAnimDll</apiname></xref>. </p> </entry>
</row>
<row>
<entry><p> <b>Transparent windows</b>  </p> </entry>
<entry><p>Transparent windows enable you to display semi-transparent bitmaps
on a window. The window must be an <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>. Methods to
create transparent windows can be found in the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> class. </p> </entry>
</row>
<row>
<entry><p> <b>Surfaces</b>  </p> </entry>
<entry><p>In ScreenPlay, applications (such as games and video) that use a
rendering API that can potentially benefit from hardware acceleration (depending
on hardware) can render directly to graphics <i>surfaces</i>. A surface is
a hardware independent buffer for holding an image or part of a scene. Surfaces
are identified using a 128 bit surface ID in a <xref href="GUID-11F60AEB-003B-3E8D-BDB9-D97F698627DF.dita"><apiname>TSurfaceId</apiname></xref> class. </p> <p>The
Window Server delegates the composition of surfaces to a composition engine
which has an adaptation part that enables device creators to take advantage
of graphics processing hardware if it is available. However, this is largely
transparent to application developers. </p> </entry>
</row>
<row>
<entry><p> <b>Direct Screen Access (DSA)</b>  </p> </entry>
<entry><p>Mainly used in the non-ScreenPlay variant, DSA enables applications
that require high frame rates (such as video and games) to bypass the Window
Server and write to the screen directly. This avoids client-server communication
and as a result is faster. However, some interaction with the Window Server
is needed to prevent the application from drawing over other application's
data. </p> <p>In ScreenPlay, Symbian recommends the use of external surfaces
in preference to DSA for most use cases. </p> </entry>
</row>
</tbody>
</tgroup>
</table> </section>
</conbody><related-links>
<link href="GUID-DC5E8C7D-D697-53E8-87F4-344301430E61.dita"><linktext>Window Server
Client-Side Library</linktext></link>
</related-links></concept>