ITmfChartTimeProvider.java

/**********************************************************************
 * Copyright (c) 2013, 2014 Ericsson, École Polytechnique de Montréal
 *
 * All rights reserved. This program and the accompanying materials are
 * made available under the terms of the Eclipse Public License v1.0 which
 * accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Bernd Hufmann - Initial API and implementation
 *   Geneviève Bastien - Moved some methods to ITmfTimeProvider
 **********************************************************************/
package org.eclipse.tracecompass.tmf.ui.viewers.xycharts;

import org.eclipse.tracecompass.tmf.ui.viewers.ITmfTimeProvider;

/**
 * Interface adding some methods specific for SWT charts to the base time
 * provider interface. Typically, the time will be shown on the x-axis.
 *
 * @author Bernd Hufmann
 */
public interface ITmfChartTimeProvider extends ITmfTimeProvider {

    /**
     * Returns a constant time offset that is used to normalize the time values
     * to a range of 0..53 bits to avoid loss of precision when converting long
     * <-> double.
     *
     * Time values are stored in TMF as long values. The SWT chart library uses
     * values of type double (on x and y axis). To avoid loss of precision when
     * converting long <-> double the values need to fit within 53 bits.
     *
     * Subtract the offset when using time values provided externally for
     * internal usage in SWT chart. Add the offset when using time values
     * provided by SWT chart (e.g. for display purposes) and when broadcasting
     * them externally (e.g. time synchronization signals).
     *
     * For example the offset can be calculated as the time of the first time
     * value in the current time range to be displayed in the chart. Add +1 to
     * avoid 0 when using logarithmic scale.
     *
     * t0=10000, t2=20000, tn=N -> timeOffset=t0-1 -> t0'=1, t1'=10001,
     * tn'=N-timeOffset
     *
     * where t0 ... tn are times used externally and t0' ... tn' are times used
     * internally by the SWT chart.
     *
     * @return the time offset
     */
    long getTimeOffset();

}