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<concept id="GUID-3B9AC7E9-3133-505F-9C1E-EB4BB4969838" xml:lang="en"><title>OpenWF

Composition Interface Overview</title><shortdesc>The OpenWF Composition Interface Component provides the Symbian

platform with a consistent interface to the open-source, cross-platform OpenWF

Composition (OpenWF-C) APIs defined by the Khronos Group. The OpenWF-C Interface

component includes the Khronos-released header files and some Symbian-specific

files. It does not provide any implementations of the APIs. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p><b>Target audience</b>: Device creators. </p>

<section><title>Introduction to OpenWF-C on Symbian</title> <p>OpenWF-C provides

a hardware abstraction layer that allows power-efficient hardware-accelerated

composition on a wide variety of hardware platforms including blitter (memory-memory)

and overlay (memory-less) hardware. OpenWF-C is particularly aimed at systems

with limited memory bandwidth, such as mobile devices. OpenWF-C enables the

UI and the window system stack to be independent of the hardware used to achieve

the composition. </p> <p>OpenWF-C uses a number of opaque handle types (<codeph>WFCHandle</codeph>)

to represent the following key concepts: </p> <ul>

<li id="GUID-4535322F-317D-5612-9B43-41CADD240F2C"><p> <b>Device</b>. An abstract

device that is capable of performing composition operations. Typically this

corresponds to a unit of graphics hardware. All composition operations and

resources are associated with a device. The <codeph>WFCDevice</codeph> subtype

represents an opaque handle to a device. </p> </li>

<li id="GUID-F64F713D-E759-52EE-B8BF-FCACC21C5664"><p> <b>Context</b>. A visual

description of a scene that is applied to a specific target. The context represents

the state required for the composition of the scene. A context can be on-screen

or off-screen but only one on-screen context per screen can render. The <codeph>WFCContext</codeph> subtype

represents an opaque handle to a composition context. </p> </li>

<li id="GUID-B5944275-D933-574F-AC47-17BBAF24AE02"><p> <b>Element</b>. Represents

the positioning and other attributes of content within the composition context.

An element is sometimes referred to as a <b>layer</b>. The <codeph>WFCElement</codeph> subtype

represents an opaque handle to an element. </p> </li>

<li id="GUID-88BA0350-A584-5C2D-BC0D-D406E06772E3"><p> <b>Source</b>. Supplies

the image data that an element can reference as the primary source of its

color data. A source is created from a stream. The <codeph>WFCSource</codeph> subtype

represents an opaque handle to a source. </p> </li>

<li id="GUID-379BCC9D-1471-5CEE-9C90-484A680BF8E5"><p> <b>Stream</b>. A container

for multiple image buffers that share the same properties. Streams encapsulate

the queuing state of the internal buffers. Streams are used for both input

and output pixel data and can be connected to multiple contexts simultaneously.

Ultimately renderers use streams to pass image data to the composition engine.

The stream format is defined as platform-specific. Streams are therefore sometimes

referred to as <b>native streams</b>. The <codeph>WFCNativeStreamType</codeph> subtype

represents the opaque handle to a stream. </p> </li>

</ul> <p> <i>Note</i>: The OpenWF-C APIs are system-level APIs and are not

intended for use by application developers. </p> </section>

<section><title>Architectural relationships</title> <p>The following diagram

shows the key OpenWF-C architectural component relationships within the Symbian

platform. </p> <fig id="GUID-84049713-A7F7-5909-8D26-EC93F53EBFDD">

<title>              OpenWF-C and related Symbian platform components    

       </title>

<image href="GUID-86A6FAC5-FF3C-5C35-A521-5C4BD3823629_d0e250728_href.png" placement="inline"/>

</fig> <ul>

<li id="GUID-03E19B9B-3CE8-5781-B94B-F68CC4D0F207"><p><xref href="GUID-0C4B86B5-530A-5839-86C1-46E7ABE281E0.dita">Window

Server</xref>. The Symbian window management and rendering component. </p> </li>

<li id="GUID-95C24C7C-3FC7-5478-8F90-E3FC668BE0EA"><p><xref href="GUID-3A2785D4-6185-50C3-8D7E-5D94CD2B7C98.dita">Render

Stages</xref>. An abstraction layer below the Window Server. </p> </li>

<li id="GUID-9859E947-820A-5085-964B-7C803C5CBFD7"><p><xref href="GUID-8BEE0411-C6E9-5840-BE22-EC271A4D97DD.dita">OpenWF-C

Engine</xref>. The implementation of the OpenWF-C interface. </p> </li>

<li id="GUID-D205AFD5-F1CD-558A-9C1B-DA189B8B52EF"><p><xref href="GUID-83510B5B-9725-5272-BF51-23A089178DAC.dita"> OpenWF-C

Support</xref>. Abstracts communication between the OpenWF-C engine and the

Surface Manager, Surface Update Server and the render stage framework and

provides a reference implementation of native stream in terms of Symbian <xref href="GUID-ADA8CECB-0E70-5B9C-8F36-0714AAF0CD13.dita">composition surfaces</xref>. </p> </li>

<li id="GUID-834FF701-708C-5AB0-9DC4-C993CF13444D"><p><xref href="GUID-C7B420DE-CEDA-5D3F-8095-71136E862CDF.dita">Surface

Manager</xref>. Allocates and manages the lifetime and use of composition

surfaces in system memory. Composition surfaces are identified by a 128-bit

identifier (<xref href="GUID-11F60AEB-003B-3E8D-BDB9-D97F698627DF.dita"><apiname>TSurfaceId</apiname></xref>). </p> </li>

<li id="GUID-9883ECD8-4739-5461-8425-1B0FAF964F1F"><p><xref href="GUID-81A0A2E9-4BB9-58BF-B2D3-08098E7E9C7C.dita"> Surface

Update Server</xref>. Provides a communication mechanism between the composition

engine and its clients. </p> </li>

<li id="GUID-CDE09188-A96F-5323-982E-D4FBC50C46D7"><p><xref href="GUID-4C166A49-31F7-5315-B797-F97DB52600BC.dita">Display

Driver</xref>. Low-level abstraction of display hardware. </p> </li>

<li id="GUID-5A97D934-DFDC-5398-8C72-049729DFBB62"><p><xref href="GUID-8C6D4350-A38D-57A1-8C8D-C777EA7E8A3E.dita">EGL</xref> (not

shown on diagram). The OpenWF-C engine and support components use EGL sync

objects for synchronization. In addition OpenWF-C clients obtain any extension

functions that the engine implements by using the EGL function, <codeph>eglGetProcAddress()</codeph>. </p> </li>

</ul> </section>

<section><title>Description</title> <p>OpenWF-C is a standard defined by the

Khronos Group (<xref href="http://www.khronos.org/" scope="external">www.khronos.org</xref>)

which defines a C API. The following table provides a link to the relevant

specification.</p> <table id="GUID-A97C8B2F-458A-5A45-88C7-7C997483845D">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<thead>

<row>

<entry>API</entry>

<entry>Specification</entry>

</row>

</thead>

<tbody>

<row>

<entry>OpenWF-C 1.0  </entry>

<entry> <xref href="http://www.khronos.org/registry/wf/specs/OpenWF_Composition_1_0_Specification.pdf" scope="external">http://www.khronos.org/registry/wf/specs/OpenWF_Composition_1_0_Specification.pdf</xref></entry>

</row>

</tbody>

</tgroup>

</table> </section>

<section><title>Header files</title> <p>The OpenWF-C Interface component includes

the Khronos-released header files shown in the following table. Use of these

standard header files helps to ensure binary compatibility for applications

across different Symbian platforms. It also provides source compatibility

between different operating systems. </p> <table id="GUID-9515BFDD-3815-561B-9587-30BB9BBEA802">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<thead>

<row>

<entry>Filename</entry>

<entry>Description</entry>

</row>

</thead>

<tbody>

<row>

<entry><filepath>wfc.h</filepath>  </entry>

<entry>Type definitions and function prototypes. </entry>

</row>

<row>

<entry><filepath>wfcext.h</filepath> </entry>

<entry>Defines additional values, functions and data types that may be available

on a platform.  </entry>

</row>

<row>

<entry><filepath>wfcplatform.h</filepath> </entry>

<entry>Platform-specific elements of the specification.  </entry>

</row>

<row>

<entry><filepath>openwfcuids.hrh</filepath> </entry>

<entry>Symbian-defined constants for representing UIDs in MMP files and elsewhere.

 </entry>

</row>

</tbody>

</tgroup>

</table> </section>

<section><title>Library file</title> <p>The OpenWF-C Interface component generates

a LIB file called <filepath>libWFC.lib</filepath>. </p></section>

<section> <title>DEF files</title> <p>The following definition (DEF) files

are delivered by the OpenWF-C Interface component in order to ensure binary

compatibility. </p> <table id="GUID-D0B2F40E-FEB3-50EF-81E1-222B80EF9436">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<thead>

<row>

<entry>Platform</entry>

<entry>DEF file </entry>

</row>

</thead>

<tbody>

<row>

<entry>ARM </entry>

<entry><filepath> /epoc32/include/platform/def/eabi/libWFCu.def</filepath>  </entry>

</row>

<row>

<entry>WINSCW </entry>

<entry><filepath> /epoc32/include/platform/def/win32/libWFCu.def</filepath> </entry>

</row>

</tbody>

</tgroup>

</table> </section>

</conbody><related-links>

<link href="GUID-8FE41C9A-8171-58A2-A808-17B81E79B11F.dita"><linktext>OpenWF Composition</linktext>

</link>

<link href="http://www.khronos.org/openwf/" scope="external"><linktext>Khronos

OpenWF Website</linktext></link>

<link href="http://www.khronos.org/developers/library/overview/openwf_overview.pdf" scope="external"><linktext>Khronos OpenWF White Paper</linktext></link>