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<concept id="GUID-D2ECF215-B53C-5659-BA86-5B658C0C2D2F" xml:lang="en"><title>Global

Surface Updates</title><shortdesc>Global surface updates are surface composition update commands

that are submitted to all displays rather than to a single one. This causes

the Surface Update Server to broadcast the update to all of the registered

composition engine instances. Each of these then determines whether the surface

is displayed on its associated screen and if so, forces an update. </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>To specify a global surface update, pass the <codeph>KAllScreens</codeph> constant

as the first argument to the <xref href="GUID-FAFD23EB-90EF-3F0C-BAB3-74FEC8DF0E06.dita#GUID-FAFD23EB-90EF-3F0C-BAB3-74FEC8DF0E06/GUID-2B032364-97A0-31A1-A08C-6D8E8ACC16E1"><apiname>RSurfaceUpdateSession::SubmitUpdate()</apiname></xref> function. </p>

<p>The use of global surface updates means that the client does not need to

track which screen the surface is visible on and call <xref href="GUID-FAFD23EB-90EF-3F0C-BAB3-74FEC8DF0E06.dita#GUID-FAFD23EB-90EF-3F0C-BAB3-74FEC8DF0E06/GUID-2B032364-97A0-31A1-A08C-6D8E8ACC16E1"><apiname>RSurfaceUpdateSession::SubmitUpdate()</apiname></xref> for

each one. The use of global surface updates is therefore recommended.</p>

<p> <i>Note</i>: You must not mix global surface updates with

updates for specific screens in the same session. </p>

<p>The global surface update feature uses the concept of a surface's <b>master

display</b>. When a surface is displayed on more than one screen, its master

display is the one that has the highest priority number. The Surface Update

Server keeps a list of the priorities of all of the displays. </p>

<p>The list of priorities is set up at startup based on the priority assigned

to the composition engine instances. (The priority of a display is defined

as the priority of its associated composition engine instance.) </p>

<section><title>Client notifications</title> <p>When global surface updates

are in use, the Surface Update Server makes copies of all of the notification

requests from the client and sends them on to each of the registered composition

engine instances. The Surface Update Server collects the completed requests

from the composition engine instance and forwards the completion status to

the client as follows: </p> <ul>

<li id="GUID-16591C0C-BB58-5D10-984F-32ED5E35F10A"><p>For all of the <codeph>NotifyWhen...()</codeph> notification

types, each composition engine instance determines whether the surface is

visible on its associated screen. If the surface is not visible, it returns <codeph>KErrNotVisible</codeph> to

the Surface Update Server. If all of the composition engine instances return <codeph>KErrNotVisible</codeph>,

the Surface Update Server returns <codeph>KErrNotVisible</codeph> to the client. </p> </li>

<li id="GUID-4E6C7843-0C0E-568A-B1D5-0DD10D052FBC"><p> <codeph>NotifyWhenAvailable()</codeph>.

For multi-buffered surfaces, the Surface Update Server sends the notification

to the client when the buffer has been released by all of the displays on

which it is visible. For single-buffered surfaces, the Surface Update Server

sends the notification to the client when the composition engine instances

that correspond to the displays on which it is visible have read the buffer

once. </p> </li>

<li id="GUID-043DE46C-130A-582C-9626-C123552A3400"><p> <codeph>NotifyWhenDisplayed()</codeph>.

The Surface Update Server sends notification to the client when the master

display has displayed the buffer. </p> </li>

<li id="GUID-114CC0D5-2955-55AC-8D7A-427D2D1B3215"><p> <codeph>NotifyWhenDisplayedXTimes()</codeph>.

The Surface Update Server sends notification to the client when the master

display has displayed the buffer the specified number of times. If the master

display becomes unavailable while the request is in progress, the Surface

Update Server reassigns it to the visible display with the next highest priority. </p> </li>

</ul> </section>

<section><title>Sequence diagrams</title> <p>The following diagrams illustrate

the sequence for global updates in a device that has two composition engine

instances registered with the Surface Update Server. These diagrams make the

following assumptions: </p> <ul>

<li id="GUID-030B0A51-35F8-57AA-93B1-0226FE46C039"><p> <i>Composition Engine

1</i> is associated with <i>Screen1</i> and <i>Composition Engine 2</i> is

associated with <i>Screen2</i>. </p> </li>

<li id="GUID-F6EDF2CF-DE85-55A2-907D-ECFA26576E7E"><p> <i>Composition Engine

1</i>'s priority is higher than <i>Composition Engine 2</i>'s. </p> </li>

</ul> <p>The first diagram shows the typical sequence when the surface is

visible on <i>Screen2</i> only. <i>Composition Engine 1</i> responds first

with <codeph>KErrNotVisible</codeph>. The Surface Update Server then considers <i>Screen2</i> to

be the surface's master display and waits for it to complete before sending

the notification to the client. </p> <fig id="GUID-14C89A10-7762-5836-AF7F-B187704510E5">

<title>              The surface is visible on Screen2 only,             

Composition Engine 1 replies before Composition Engine              2    

       </title>

<image href="GUID-5F9BEEF7-19BC-550F-BD97-60F70B55E906_d0e251994_href.png" placement="inline"/>

</fig> <p>In the next diagram, the surface is still visible on <i>Screen2</i> only.

This time, however, <i>Composition Engine 2</i> replies before <i>Composition

Engine 1</i>. The Surface Update Server considers <i>Composition Engine 1</i> to

be the master until it receives an error (<codeph>KErrNotVisible</codeph> in

this example) from <i>Composition Engine 1</i>. It then considers <i>Backend2</i> to

be the master. </p> <p>Notice that although <i>Screen2</i> has become the

master, <codeph>RequestComplete()</codeph> goes to the client at the point

that <i>Composition Engine 1</i> returns the error. This is because <i>Backend2</i> replied

before <i>Backend1.</i>  </p> <fig id="GUID-0708D124-F89D-5BCA-85B0-E28E4CCD26C7">

<title>              The surface is visible on Screen2 only,             

Composition Engine 2 replies before Composition Engine              1    

       </title>

<image href="GUID-B4653180-46EB-58A8-B2A8-0DD2C3D30FE7_d0e252044_href.png" placement="inline"/>

</fig> <p>In this final diagram, the surface is visible on both screens. <i>Screen1</i> is

considered the surface's master display and the client is notified when <i>Composition

Engine 1</i> completes. When <i>Composition Engine 2</i> completes, the Surface

Update Server discards its notification. </p> <fig id="GUID-FA4BE8A3-33A2-53E7-9124-53D404B0305A">

<title>              The surface is visible on both screens.            </title>

<image href="GUID-467EF3F5-754B-550A-A9C7-246D68C91F0A_d0e252064_href.png" placement="inline"/>

</fig> </section>

<section><title>Example</title> <p>The following code snippet shows using

the global surface update feature to request composition to all of the screens

that are registered with the Surface Update Server. </p> <codeblock id="GUID-45C71218-12FC-58A9-877E-27D642F5E949" xml:space="preserve">TRequestStatus  status;

RRegion *region;

// Signifies all screens.

TInt screen = KAllScreens;

// The current buffer for composition.

TInt theBuffer = 0; 

TSurfaceId surfaceId;

// Set surface ID.

...

// Render to the surface.

...

// Broadcast the request to all registered screens.

surfaceUpdateSession.SubmitUpdate(screen, surfaceId, theBuffer, NULL);

</codeblock> </section>

</conbody><related-links>

<link href="GUID-8E8FE99A-5F4D-5B0F-87AB-A58EB4BEB6E9.dita"><linktext>Surface Update

Component Overview</linktext></link>

<link href="GUID-63CB6C7E-44EC-5D0B-A37D-FE78F7D76592.dita"><linktext>Graphics

Composition Collection</linktext></link>

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

Composition Surfaces</linktext></link>

</related-links></concept>