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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
window surfaces 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>Threading</b>. Because of the limitations of
the Window Server API, clients <b>must</b> create and use an EGL window surface
in the thread in which its <codeph>RWindow</codeph> was created. This means
that the following are <b>not</b> supported and will lead to undefined behavior:</p><ul>
<li><p>Creating an EGL window surface in thread <i>B</i> using an <codeph>RWindow</codeph> that
was created in thread <i>A</i>. </p></li>
<li><p>Using an EGL window surface in thread <i>B</i> when that EGL window
surface and its <codeph>RWindow</codeph> were created in thread <i>A</i>. </p></li>
</ul><p>For example, in the second scenario, EGL in thread <i>B</i> may fail
when it attempts to get the window size from the <codeph>RWindow</codeph> in
thread <i>A</i>.</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><display id></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_d0e211044_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>