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<concept id="GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7" xml:lang="en"><title>External

Surfaces Overview</title><shortdesc>This topic provides an introduction to displaying an external surface

on a window. The surface is then known as a background surface. This feature

is available in ScreenPlay only. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> <b>Variant</b>: <xref href="GUID-D93978BE-11A3-5CE3-B110-1DEAA5AD566C.dita">ScreenPlay</xref>. <b>Target

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

<p>There are two main use cases for using external surfaces in this way. One

is to display a video, in which case DevVideo renders the content. The other

main use case is an OpenGL ES background surface, in which case the client

issues OpenGL ES rendering commands. This topic covers how to get the surface

onto the screen and not rendering the content to the surface. </p>

<section><title> Key concepts</title> <p>The following diagram illustrates

some of the key concepts that are used in the documentation of surfaces. </p> <fig id="GUID-F134C262-EC19-5925-A188-2C7C2CD5EEEA">

<title>Composition of the UI surface and an external surface, showing the

             viewport and extent</title>

</fig> <dl>

<dlentry>

<dt>Graphics surface</dt>

<dd><p>A graphics surface (usually simply called a <i>surface</i>) is a hardware-independent

memory buffer for holding an image or part of a scene. A surface has a set

of attributes, the most important of which is its ID (which is a <xref href="GUID-11F60AEB-003B-3E8D-BDB9-D97F698627DF.dita"><apiname>TSurfaceId</apiname></xref>). </p> </dd>

</dlentry>

<dlentry>

<dt>UI surface</dt>

<dd><p>The UI surface is a special surface onto which the Window Server renders

all of the UI content. It is created automatically during system start up

and corresponds to the frame buffer in the non-ScreenPlay variant. The UI

surface is semi-transparent and is always the topmost layer.</p> </dd>

</dlentry>

<dlentry>

<dt>External surface</dt>

<dd><p>An external surface is any surface other than the UI surface—for example,

a surface that holds a video or to which OpenGL ES content is rendered. External

surfaces are always opaque. When an external surface is attached to a window,

the Window Server creates a transparent hole in the UI surface to reveal the

external surface. </p> </dd>

</dlentry>

<dlentry>

<dt>Viewport</dt>

<dd><p>The viewport is a rectangular area of an external surface all or part

of which is to be displayed. You can think of the viewport as the source. </p> </dd>

</dlentry>

<dlentry>

<dt>Extent</dt>

<dd><p>The extent is a rectangular area in the composition scene in which

all or part of the viewport is placed. The content of the viewport can be

scaled and rotated within the extent relative to its normal size and orientation.

The extent is normally a window to which the external surface is attached. </p> </dd>

</dlentry>

</dl> <p>The following diagram provides a cross-section view through the surfaces

shown in the previous figure. Notice that the UI surface is the topmost layer

and that it contains a hole through which the external surface

can be seen.</p> <fig id="GUID-4DB99814-988F-5D51-A1A7-E864B6DA6DFB">

<title>              A cross section through the surfaces, showing the display

output            </title>

</fig> </section>

<section id="GUID-F9D7659B-1325-5DC2-9D7A-9B6C0DFB8A62"><title>Supported Uses</title> <p>You

can: </p> <ul>

<li id="GUID-97CAD13E-1C70-59FF-B271-F3E77198086A"><p>Display an external

surface (for example, video content or a viewfinder image) within a window. </p> </li>

<li id="GUID-BD8FFB28-D56C-581B-9E1C-B2BD97FDAFBC"><p>Dynamically set or remove

a background surface across multiple windows on the same screen without having

to register and unregister the surface. This reduces resource churn and content

transfer. </p> </li>

<li id="GUID-0A3FD92E-7E99-5961-BC5A-3FBB970A7889"><p>Reconfigure the attributes

of the surface such as its extent, viewport and orientation, after it is set

as a background. </p> </li>

<li id="GUID-6E962607-1E7D-516E-B855-15A1A67923B6"><p>Reposition the displayed

surface on the window. </p> </li>

<li id="GUID-26E561E7-92BB-5EBA-A3B9-F660507A258D"><p>Zoom in and out of the

contents of the surface. </p> </li>

<li id="GUID-287D3286-209B-5E01-B1C6-2373A2B07172"><p>Place the surface content

in a specified window area rather than filling the entire window. </p> </li>

<li id="GUID-6F2DCF0C-32D7-53CD-A2DD-4DBE662015B5"><p>Crop the surface content

rather than using the entire surface. </p> </li>

<li id="GUID-8E49A7FB-0709-5127-8C94-104C512EA6AC"><p>Rotate the contents

of the background surface by quadrant angles. </p> </li>

<li id="GUID-5631047A-A8AD-59DF-82FF-021964BA571D"><p>Flip the background

surface from top to bottom and rotate it by 180° to achieve a mirroring effect. </p> </li>

</ul> <p>The following diagrams shows some surface configuration use cases. </p> <fig id="GUID-FF25ED24-7A3D-5C4B-A711-D6AEA53E972F">

<title>              Surface configuration use cases            </title>

</fig> </section>

<section id="GUID-7EAB8F5D-6290-5B63-B396-8A1FAE7D91A5"><title> Configuration</title> <p>There

are a number of ways in which dynamically updated content can be configured

to appear on a window. </p> <p><b>A single content surface filling the window </b> </p> <p>External

content can be fitted onto a Window Server window. Each axis of the surface

can be stretched independently of the other axis. The window must be a visible

client window: <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> or <xref href="GUID-A5DFCFA7-7B2D-3872-B6D0-4526DF743630.dita"><apiname>RBlankWindow</apiname></xref>. </p> <p><b>Placement

of a single surface on a selected area of the window </b> </p> <p>The position

and display size for the external content can be specified as an area within

the Window Server window, rather than filling the window. The window must

be a visible client (<xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita"><apiname>RWindow</apiname></xref> or <xref href="GUID-A5DFCFA7-7B2D-3872-B6D0-4526DF743630.dita"><apiname>RBlankWindow</apiname></xref>)

as before. You specify the area by using <xref href="GUID-59A10068-E37A-37CF-85C9-36D8DA6619FA.dita#GUID-59A10068-E37A-37CF-85C9-36D8DA6619FA/GUID-8984E1F8-2807-301D-B82B-A52CC4254B04"><apiname>TSurfaceConfiguration::SetExtent(const

TRect&amp;           aExtent)</apiname></xref>. </p> <p>After the extent is specified,

its size does not change if the window size changes but its position moves

to maintain its relative position on the window. </p> <p><b>Clipping of a

surface </b> </p> <p>Video sometimes needs to appear cropped, so that a sub-area

of the video is displayed instead of the full image. The crop viewport is

specified in surface co-ordinates. The cropped viewport fills the output extent

(or the window when the extent is not specified). The content appears scaled

if the size of the viewport does not match the size of the extent (or the

window). </p> <p><b>Scaling </b> </p> <p>It is possible to arbitrarily scale

a surface to user specifications using the extent and viewport features. Each

axis is scaled independently. When the extent and viewport are coincident,

no scaling occurs. Filtering can be applied by the implementation of stretching

and shrinking. </p> <p><b>Rotation </b> </p> <p>The viewport can be displayed

rotated relative to its normal orientation. For example, if there is a fixed

camera on the front of a device and the device is rotated by 90°, the image

captured by the camera needs to be rotated by 90° in the other direction to

get the expected result. The orientation is always relative to the current

device orientation. </p> <p><b>Flipping </b> </p> <p>An external surface can

be flipped from top to bottom around the x axis. </p> <p><b>Atomic combination

of these operations </b> </p> <p>All the above mentioned configurations can

be specified and combined unambiguously for a particular content on a particular

window. You can specify parameters for a combination of these configurations

in a single operation. </p> <p><b>Changing surfaces </b> </p> <p>The surface

assigned to a window can be changed. </p> <p><b>Reconfiguring </b> </p> <p>It

is possible to change the configuration options applied to a surface without

re-assigning the surface. </p> <p><b>Sharing surfaces </b> </p> <p>Content

surfaces are transferable and sharable between windows. </p> <p>The initial

registration step ensures that any resources allocated to the content surface

are held while the surface is removed from one window and added to another.

This reduces the likelihood of failure between operations. </p> </section>

<section><title>API Summary</title> <p>This section provides a summary of

the classes and functions that you use to manage surfaces: </p> <ul>

<li id="GUID-D7C9343C-BFAB-5153-B3E6-E5EBA5859570"><p><xref href="GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7.dita#GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7/GUID-3E1EF2ED-7E9C-541F-A439-F2CBA5B6F211">RWindowBase</xref>  </p> </li>

<li id="GUID-5AD3B9D5-60E8-5A2A-9C6B-4C914540FE9E"><p><xref href="GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7.dita#GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7/GUID-1DC9E4DF-248F-59A6-92A9-F756F73414B3">TSurfaceConfiguration</xref>  </p> </li>

<li id="GUID-2627F547-B979-5682-A69A-97D89969F9B3"><p><xref href="GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7.dita#GUID-495EA1C8-E95F-54AE-B4D1-0F463003C2D7/GUID-E2A62988-58F8-5021-BA44-25AE3C3D95B5">RWsSession</xref>  </p> </li>

</ul> </section>

<section id="GUID-3E1EF2ED-7E9C-541F-A439-F2CBA5B6F211"><title>RWindowBase </title> <ul>

<li id="GUID-7A5D0A6F-C0B6-5D87-B0F4-99C92FA8227B"><p> <codeph>SetBackgroundSurface(const

TSurfaceConfiguration                 &amp;,TBool)</codeph> sets the background

of the window to be a given surface. The <xref href="GUID-59A10068-E37A-37CF-85C9-36D8DA6619FA.dita"><apiname>TSurfaceConfiguration</apiname></xref> argument

contains the surface ID and the configuration attributes. Another form of

the function simply takes a surface ID as an argument, which provides less

control and auto-stretches the surface to fill the window. </p> </li>

<li id="GUID-C86F37F7-5017-56F3-9B14-E3B8E0EC0E8A"><p> <codeph>RemoveBackgroundSurface()</codeph> removes

any background surface that has been set to the window. </p> </li>

<li id="GUID-11ABFBDE-556F-5096-810E-6BBA2C81C4B1"><p> <codeph>GetBackgroundSurface()</codeph> retrieves

a copy of the current configuration for the background surface attached to

the window. </p> </li>

</ul> <p>See <xref href="GUID-1460DD8F-9AA1-3B99-8FFD-F309959CCA34.dita"><apiname>RWindowBase</apiname></xref>. </p> </section>

<section id="GUID-1DC9E4DF-248F-59A6-92A9-F756F73414B3"><title> TSurfaceConfiguration</title> <p>This

class encapsulates the surface configuration attributes that can be specified

while setting the background surface of a window. If the values for the attributes

are not set, the default values for the corresponding attribute are used. </p> <p>Symbian

recommends that the client validates the surface configuration data before

passing it on to the server. Invalid data that inadvertently slips through

the client-side validation mechanism, or maliciously bypasses it, causes a

panic. </p> <p>See <xref href="GUID-59A10068-E37A-37CF-85C9-36D8DA6619FA.dita"><apiname>TSurfaceConfiguration</apiname></xref>. </p> </section>

<section id="GUID-E2A62988-58F8-5021-BA44-25AE3C3D95B5"><title> RWsSession</title> <ul>

<li id="GUID-B1A1CE19-6E12-5BA7-B79A-A6D7C44F5920"><p> <codeph>RegisterSurface()</codeph> registers

a surface for use in composition on the screen associated with this device

within this session. </p> </li>

<li id="GUID-6678C53D-F0B5-5ADD-BCC7-43FC31E81FEE"><p> <codeph>UnregisterSurface()</codeph> removes

the surface from the session’s register of surfaces that are used in composition

on the screen associated with this device. </p> </li>

<li id="GUID-9F5FF304-794C-5BC3-B16E-F036C859F1E2"><p> <codeph>PreferredSurfaceConfigurationSize()</codeph> returns

the window server’s preferred size for the <codeph>TSurfaceConfiguration</codeph> object,

used for <xref href="GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79.dita#GUID-683603DD-F3D3-3193-BEB3-8236C7DE7F79/GUID-AC4FBD36-8CC7-3191-B266-1805DEDE6D50"><apiname>RWindow::SetBackgroundSurface()</apiname></xref>. </p> </li>

</ul> <p>See <xref href="GUID-643DDA78-C7A7-386D-AB3F-8710141DDDA9.dita"><apiname>RWsSession</apiname></xref>. </p> </section>

<section><title>Example</title> <p>This code snippet is provided for illustrative

purposes only. A Window Server client application wants to run a 3D game full-screen

at the native physical resolution of the display (either current or selected

using a display controlling system application). This example assumes that

the <xref href="GUID-BA6FEFAE-8891-3286-A38F-2EA522D7A27E.dita"><apiname>MDisplayMapping</apiname></xref> interface has already been obtained,

as shown in <xref href="GUID-B1CB6374-2C2B-5D6C-9A7C-6E49D8F235B8.dita">Display

Control and Mapping in the Window Server Client</xref>. </p> <codeblock id="GUID-DE5C6DB0-1096-5BA3-8BB7-78AE3B6619B1" xml:space="preserve">// Establish connection and get display mapping interface.

RWindowGroup group = RWindowGroup(iSession);

RWindow window(iSession);

group.Construct(1, iScreenDevice);

window.Construct(group, 2);

TRect winExtent;

iDisplayMapping.GetMaximumWindowExtent(winExtent);

window.SetExtent(winExtent);

// Map window size to composition coordinates

TRect surfaceExtent;

iDisplayMapping.MapCoordinates(EApplicationSpace, winExtent,

    ECompositionSpace, surfaceExtent);

RSurfaceManager::TSurfaceCreationAttributes attribs;

attribs.iSize = surfaceExtent.Size();

// Set up other attributes and create surface

window.SetBackgroundSurface(surface);

window.Activate();

</codeblock> <p>A similar approach can be used by other surface content providers,

such as video. </p> </section>

</conbody><related-links>

<link href="GUID-859CAA08-59C9-5FD3-98DE-6BDD0D6ED50B.dita"><linktext>Graphics

Composition</linktext></link>

<link href="GUID-ADA8CECB-0E70-5B9C-8F36-0714AAF0CD13.dita">

<linktext>Graphics Surfaces</linktext></link>

<link href="GUID-1F9A47CE-7F4C-52BD-8823-25D5D1BEF42F.dita"><linktext>Window Server

Client-Side Library Concepts</linktext></link>

<link href="GUID-0EBE5733-A267-5F4A-85AD-87C3ECF80731.dita"><linktext>Dynamic Resolution

Switching</linktext></link>

<link href="GUID-652DA0DD-AB1D-58A4-A6D2-27B5BAA506FF.dita"><linktext>Flipping

and Rotating an External  Surface</linktext></link>

</related-links></concept>