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<concept id="GUID-894AB487-C127-532D-852B-37CB0DEA1440" xml:lang="en"><title>Symbian-Specific

Behavior</title><shortdesc>This topic provides information about the points that the EGL specification

explicitly states are platform-specific. This information is aimed at both

users and implementers of EGL on the Symbian platform. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-5F4317DF-EEDE-434C-906D-A354367AE38D"><title>Symbian windows</title> <p>EGL windows are tied to Symbian

windows. To create an on-screen rendering surface, a Window Server window

with attributes corresponding to the desired <codeph>EGLConfig</codeph> must

be created first. The <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> class is a handle to a server-side

window that can be displayed and drawn to, and whose redraws are performed

by the application. </p> <p><b>Buffer handling</b>. EGL window surfaces have

two buffers, known as the front and back buffers. This means that the client

application can draw to the back buffer, while the front buffer is being composed

to the screen. The client must call <codeph>eglSwapBuffers()</codeph> to post

the back buffer to the screen. </p><p>EGL 1.4 introduces a preserve buffer

feature. When this is supported by the implementation, the content of the

buffer can be preserved from one frame to the next. This means that the client

can provide incremental drawing operations rather than the entire drawing

operations for each frame. When the implementation supports this feature,

it is usually off by default. This means that legacy applications that do

not expect this feature are not slowed down by the unnecessary copying of

the buffer contents.</p> <p><b>Window resizing</b>. A window can be resized

using one of the Window Server or UI Framework APIs, such as <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita#GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79/GUID-BCD76117-54A3-3CD5-8911-E867512BF85B"><apiname>RWindow::SetExtent()</apiname></xref> or <xref href="GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160.dita#GUID-B06F99BD-F032-3B87-AB26-5DD6EBE8C160/GUID-B680C675-2146-3162-AAAC-F3E88FA8B045"><apiname>CCoeControl::SetExtent()</apiname></xref>. When these APIs are called on a window that is bound to an EGL window surface,

the EGL implementation is expected to handle the situation by adjusting its

internal buffers. Applications need not do anything specific with regard to

EGL APIs. Depending on the type of application, APIs may want to adjust their

rendering operations—for example, clip or scale the contents. </p> <p>EGL

handles the resize in the next call to <codeph>eglSwapBuffers()</codeph> by

creating a new surface for the resized window. If the preserve buffer option

is in use, this function also copies across all the pixels from the old surface

that overlap the new surface, although the exact details depend

on the implementation. A client application may therefore need to provide

extra drawing operations, for example, if the window is made larger.</p> <p> <b>Screen

rotation</b>. There is no specific EGL handling for screen rotation—instead

screen rotation is handled in the same way as a change of screen resolution.

Applications can detect screen rotation by listening to the Window Server

event <xref href="GUID-CC1E6B2E-F68F-3A00-B4EA-4917007F7320.dita"><apiname>EEventScreenDeviceChanged</apiname></xref>. However, applications

do not normally use the Window Server API directly, because they are built

on top of the UI Framework layer. This layer provides a different mechanism

to notify applications using—for example, <xref href="GUID-3AC2CDAC-0291-309F-A020-049BC9F2CF90.dita#GUID-3AC2CDAC-0291-309F-A020-049BC9F2CF90/GUID-5723655E-FC84-35F1-A0E1-FCE92CEBC196"><apiname>CCoeAppUi::HandleScreenDeviceChangedL()</apiname></xref>. </p> <p>When

one of the these events is detected, the application may need to resize its

windows and update its content accordingly. If the application wants to accept

the system rotation, it does not need to rotate its content. However, some

applications may want to maintain a fixed physical orientation. They would

then need to rotate the window content in order to counteract the physical

rotation. </p> </section>

<section id="GUID-9BC770D9-3736-495E-8485-19D71700C50D"><title>Symbian pixmap types</title> <p>An EGL implementation can

support the <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> pointer as an <codeph>EGLNativePixmapType</codeph>.

This means that it is possible to create an <codeph>EGLSurface</codeph> to

render to a <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref>. </p> <p> <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> bitmaps

are managed by the <xref href="GUID-71DADA82-3ABC-52D2-8360-33FAEB2E5DE9.dita">Font

and Bitmap Server</xref>. The format is internal to Symbian, but the Image

Converter API can be used to convert them to standard formats. The <xref href="GUID-683A1D42-2764-3EB7-BD19-9E12559199AB.dita"><apiname>CFbsBitmap</apiname></xref> type

has limitations with regard to hardware acceleration. </p> </section>

<section id="GUID-44553B50-C48E-4E6B-AD9C-F3BC7D9D5347"><title>Display handling</title> <p>Most EGL calls include an <codeph>EGLDisplay</codeph> parameter.

The EGL specification describes this as "the abstract display on which graphics

are drawn". On some systems, this corresponds to a physical screen. However,

the details are platform specific and on Symbian systems, it does <i>not</i> correspond

to a physical screen. When working on the Symbian platform, it is generally

more useful to think of an <codeph>EGLDisplay</codeph> as the EGL session. </p> <p>On

Symbian systems, you usually use a single <codeph>EGLDisplay</codeph>. You

get this by a call to <codeph>eglGetDisplay()</codeph> and passing <codeph>EGL_DEFAULT_DISPLAY</codeph> as

the <codeph>&lt;display id&gt;</codeph> parameter. </p> <p>The physical screen

on which the content is displayed is determined by the window's parent window

group. In Symbian, every window (<xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref>) has a parent

window group (<xref href="GUID-64D4D428-D65F-3D9D-A0D4-C8338C848B25.dita"><apiname>RWindowGroup</apiname></xref>), as shown in the following

diagram. When you create a window group, you can specify the screen on which

it is to be shown. </p> <fig id="GUID-5D5F3C6A-4CFA-5307-8B2D-D2881799D664">

<title>Each window has a parent window group which is associated with a screen</title>

<image href="GUID-CF9EF400-DE1F-55F7-BD33-C4CD80462971_d0e243967_href.png" placement="inline"/>

</fig> <p>When you create a window surface in EGL using <codeph>eglCreateWindowSurface</codeph>,

you pass in the <codeph>RWindow</codeph> as an argument. The window surface

is then displayed on the screen associated with that window's parent window

group. Currently a window can exist on only one screen. </p> </section>

</conbody><related-links>

<link href="GUID-D252E75C-C8CA-5C51-8DA3-95B937A1295C.dita"><linktext>EGL Interface

Component</linktext></link>

<link href="GUID-DC8BFEF5-DA50-52DA-8CE2-5729A4A005F6.dita"><linktext>EGL Collection

Overview</linktext></link>

</related-links></concept>