diff -r d189ee25cf9d -r 3533d4323edc emailuis/uicomponents/inc/fsinteractioninterval.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/emailuis/uicomponents/inc/fsinteractioninterval.h	Wed Sep 01 12:28:57 2010 +0100
@@ -0,0 +1,108 @@
+/*
+* Copyright (c) 2006-2007 Nokia Corporation and/or its subsidiary(-ies). 
+* All rights reserved.
+* This component and the accompanying materials are made available
+* under the terms of "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:
+*
+* Description:  THuiInteractionInterval is a utility class that can be used 
+*                as specify intervals that adapt to user input.
+*
+*/
+ 
+
+#ifndef __FSINTERACTIONINTERVAL_H__
+#define __FSINTERACTIONINTERVAL_H__
+
+
+#include <e32base.h>
+
+/**
+ * THuiInteractionInterval is a utility class that can be used to determine
+ * the correct animation interval time, while taking into account how much time has
+ * elapsed since the last time the interval was determined. 
+ *
+ * An interaction interval is useful for example when animating a list selector. By default,
+ * the time interval for moving between two items could be 500 ms, but if
+ * the user moves faster than this, the selector's animation may be 
+ * unnecessarily delayed. In this situation, the interaction interval would
+ * shorten the time interval for the moving animation, if necessary, to keep
+ * better in sync with how quickly the user is moving in the list.
+ */
+class CFsInteractionInterval: public CBase 
+    {
+public:
+
+    /* Constructors and destructor. */
+
+    /**
+     * Initializes the interaction interval.
+     *
+     * @param aScalar  Determines how strongly the interval adapts. 
+     *
+     * @see SetScalar()
+     */
+    CFsInteractionInterval(TReal32 aScalar = 2.0f);
+
+
+    /* Methods. */
+
+    /**
+     * Sets the adaptation scalar. Determines how strongly the interval
+     * will adapt to the elapsed time since the last evaluation.
+     *
+     * For example, 1.0 would mean that the maximum interval time is the 
+     * time elapsed between the current evaluation and the
+     * previous one. In this case, when the animation frequency 
+     * stays the same, each sequence would have time to complete
+     * before the next sequence begins. When the scalar is 2.0, the
+     * maximum is twice the elapsed time, meaning that the 
+     * ongoing animation sequence would always be finished halfway 
+     * when the next sequence begins. This produces a smoother
+     * end result.
+     *
+     * @param aScalar  New adaptation scalar.
+     */
+     void SetScalar(TReal32 aScalar);
+    
+    /**
+     * Returns the current adapation scalar.
+     *
+     * @return Adaptation scalar.
+     */
+     TReal32 Scalar() const;
+
+    /**
+     * Evaluates the current interval. The evaluated interval will always 
+     * be at least as large as the elapsed time since the last evaluation, 
+     * but at most <code>aIntervalTime</code>. 
+     *
+     * @param aIntervalTime  The requested normal interval time.
+     *
+     * @return  The evaluated interval, effective during the current frame.
+     *
+     * @see SetScalar()
+     */
+     TInt Interval(TInt aIntervalTime);
+    
+    
+private:
+
+    TTime iLastTime;
+    
+    /** Interval scalar. */
+    TReal32 iScalar;
+    
+    /** Last time interaction interval was determined. */
+    TUint32 iLastTimeMs;
+
+    };
+
+
+#endif  // __FSINTERACTIONINTERVAL_H__