<?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-2BF409EA-82BF-407C-B048-DA0973B7F61D" xml:lang="en"><title>Optimizing

feedback latency</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The general latency requirement for touch feedback is 30 milliseconds.

For direct feedback it is not always possible to achieve this, as in high

CPU load cases it may take more than 30 ms already before the pointer event

reaches the application. </p>

<p>However, you can also affect the latency in your application: the maximum

additional latency for direct feedback is as long as it takes for the longest

running <codeph>RunL</codeph> of any active object running in application’s

thread to execute. Hence keeping all <codeph>RunL</codeph> functions short

improves the feedback latency (and of course also improves the overall responsiveness

of the application). </p>

<p>Another way of improving the latency is optimizing redrawing in such a

way that only the necessary area of the screen is drawn. </p>

<p>For example, if there are 20 buttons in the application and one of them

is pressed down by a pointer event, then only that button should be redrawn

and not the whole screen. This optimization improves both direct and area

registry based feedback, because the window server cannot receive pointer

events from the touch driver in case it is performing a draw operation, and

unnecessarily massive draw operations can thus have significant effect on

the latency.</p>

<p>Finally, it is recommended that you trigger direct feedback in <codeph>HandlePointerEventL</codeph> as

the first thing before doing any other processing, such as redrawing.</p>