<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-0B2421FD-8431-5DDA-9FE3-046734AE495E" xml:lang="en"><title>Window

Surface Implementation</title><shortdesc>This topic provides an introduction to implementing EGL window

surfaces on the Symbian platform. These are used for onscreen rendering into

windows that are provided by the Symbian platform (rather than EGL). The details

of how to implement window surfaces depend on whether the ScreenPlay variant

is in use. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

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

<section><title>Symbian windows</title> <p>Window surfaces are created by

the <codeph>eglCreateWindowSurface()</codeph> function, to which is passed

a handle to a window provided by the Symbian <xref href="GUID-2C443E6F-BC3D-5252-8098-9F850AA88A35.dita">Window

Server</xref>. Key Window Server classes include the following: </p> <ul>

<li id="GUID-CE332026-A8BC-57D8-B845-F0C41CCBA4C2"> <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>,

which is a handle to a standard window. </li>

<li id="GUID-DFC36F32-71B2-5502-B4A9-B95C6548751D"><xref href="GUID-643DDA78-C7A7-386D-AB3F-8710141DDDA9.dita"><apiname>RWsSession</apiname></xref>,

which is the Window Server session class. This is required to create Window

Server objects.  </li>

<li id="GUID-B17680DB-00AD-5B8C-8199-5E03B9CB71E8"> <xref href="GUID-30479BE3-296E-3B4D-914D-B080ABD733E4.dita"><apiname>CWsScreenDevice</apiname></xref>,

which is a Window Server client-side object representing the screen. </li>

</ul> </section>

<section><title> Non-ScreenPlay </title> <p>In the non-ScreenPlay variant

there is no composition engine and both Symbian API drawing (for example,

through <xref href="GUID-0AEE5955-C530-35F1-A904-69183331B294.dita"><apiname>CWindowGc</apiname></xref>) and EGL client API drawing are rendered

to a single display. The EGL implementation can achieve this in a number of

ways, including: </p> <ul>

<li id="GUID-332CAE78-9EBD-5DAF-A640-FEE2CBC48B73"><p>Using Direct Screen

Access (DSA) to render the EGL client API drawing directly to the screen.

This is done in cooperation with the Window Server, which provides clipping

instructions. This approach is particularly suitable when graphics acceleration

hardware is available. </p> </li>

<li id="GUID-646EE6E5-6194-5862-8225-9D756EA55ACC"><p>Rendering the EGL client

API drawing to an offscreen <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> and then calling

a Window Server API to blit the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> onto the screen,

with any necessary clipping. </p> </li>

</ul> </section>

<section><title>ScreenPlay</title> <p>ScreenPlay has introduced the <xref href="GUID-0DC3E5AA-1706-5255-ACD6-E7AB732E1095.dita">Graphics Composition Collection</xref>,

which enables a number of <b>surfaces</b> to be arranged in layers and to

be composed together to produce the final output on the display. In this section,

these surfaces are called <b>composition surfaces</b> in order to distinguish

them from EGL surfaces. Each composition surface is mapped to memory, which

can be specialized graphics memory for faster performance. </p> <p>All

Window Server drawing (such as the application UI) is rendered to a composition

surface called the <b>UI surface</b>, which is usually the topmost layer and

can be semi-transparent. </p><p>When the EGL implementation creates an EGL

window surface for a Symbian window (represented by <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>),

the EGL implementation must do the following: </p><ul>

<li id="GUID-ECAF9CD5-0770-5D51-827B-9E30A1A14478"><p>Create a new composition

surface with the same width and height as the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>. </p> </li>

<li id="GUID-69D40D06-D691-5DC4-8AB8-7C93F74EDAE4"><p>Position the composition

surface in a layer below the UI layer, directly below the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>. </p> </li>

<li id="GUID-19391759-8C65-5D17-96C7-A9155303442E"><p>Make the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> transparent

in order for the composition surface to show through. </p> </li>

</ul><p/><p>All of the EGL client API drawing to the EGL window surface

is then rendered to the composition surface and the application's UI appears

as a semi-transparent layer above it. </p><p>When a window is resized, a new

composition surface needs to be created with the new width and height, and

positioned as a layer below the <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> in place of the

previous composition surface. </p><p>A composition surface can have more than

one pixel buffer associated with it (each buffer has the same dimensions).

For an EGL window surface, the composition surface should have two buffers

for double-buffered drawing. This means, for example, that OpenVG commands

can draw to the <b>back buffer</b>, while the <b>front buffer</b> is being

composed to the screen. </p> </section>

</conbody><related-links>

<link href="GUID-DC3A8785-3ED3-5696-A5ED-AB66588A5C14.dita"><linktext>EGL Porting

Guide</linktext></link>

<link href="GUID-0DC3E5AA-1706-5255-ACD6-E7AB732E1095.dita"><linktext>Graphics

Composition Collection Overview</linktext></link>

<link href="GUID-599C9890-3AC8-46D3-A8C3-34CAAB5A61CF.dita"><linktext>Implementing

eglCreateWindowSurface</linktext></link>

<link href="GUID-42984078-3DEB-41C7-AC76-C769F7CDB4D0.dita"><linktext>Implementing

eglSwapBuffers</linktext></link>

</related-links></concept>