1 <?xml version="1.0" encoding="utf-8"?>

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-2BF409EA-82BF-407C-B048-DA0973B7F61D" xml:lang="en"><title>Optimizing

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

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

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

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

    17 reaches the application. </p>

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

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

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

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

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

    23 of the application). </p>

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

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

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

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

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

    29 registry based feedback, because the window server cannot receive pointer

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

    31 unnecessarily massive draw operations can thus have significant effect on

    32 the latency.</p>

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

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

    35 </conbody></concept>