annotate layer/RenderTimer.h @ 1127:9fb8dfd7ce4c spectrogram-minor-refactor

Fix threshold in spectrogram -- it wasn't working in the last release.
There is a new protocol for this. Formerly the threshold parameter had a
range from -50dB to 0 with the default at -50, and -50 treated internally
as "no threshold". However, there was a hardcoded, hidden internal threshold
for spectrogram colour mapping at -80dB with anything below this being rounded
to zero. Now the threshold parameter has range -81 to -1 with the default
at -80, -81 is treated internally as "no threshold", and there is no hidden
internal threshold. So the default behaviour is the same as before, an
effective -80dB threshold, but it is now possible to change this in both
directions. Sessions reloaded from prior versions may look slightly different
because, if the session says there should be no threshold, there will now
actually be no threshold instead of having the hidden internal one.

Still need to do something in the UI to make it apparent that the -81dB
setting removes the threshold entirely. This is at least no worse than the
previous, also obscured, magic -50dB setting.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef RENDER_TIMER_H
#define RENDER_TIMER_H

#include <chrono>

class RenderTimer
{
public:
    enum Type {
	/// A normal rendering operation with normal responsiveness demands
	FastRender,

	/// An operation that the user might accept being slower
	SlowRender,

	/// An operation that should always complete, i.e. as if there
	/// were no RenderTimer in use, but without having to change
	/// client code structurally
	NoTimeout
    };
    
    /**
     * Create a new RenderTimer and start timing. Make one of these
     * before rendering, and then call outOfTime() regularly during
     * rendering. If outOfTime() returns true, abandon rendering!  and
     * schedule the rest for after some user responsiveness has
     * happened.
     */
    RenderTimer(Type t) :
	m_start(std::chrono::steady_clock::now()),
	m_haveLimits(true),
	m_minFraction(0.1),
	m_softLimit(0.1),
	m_hardLimit(0.2),
	m_softLimitOverridden(false) {

	if (t == NoTimeout) {
	    m_haveLimits = false;
	} else if (t == SlowRender) {
	    m_softLimit = 0.2;
	    m_hardLimit = 0.4;
	}
    }


    /**
     * Return true if we have run out of time and should suspend
     * rendering and handle user events instead. Call this regularly
     * during rendering work: fractionComplete should be an estimate
     * of how much of the work has been done as of this call, as a
     * number between 0.0 (none of it) and 1.0 (all of it).
     */
    bool outOfTime(double fractionComplete) {

	if (!m_haveLimits || fractionComplete < m_minFraction) {
	    return false;
	}
	
	auto t = std::chrono::steady_clock::now();
	double elapsed = std::chrono::duration<double>(t - m_start).count();
	
	if (elapsed > m_hardLimit) {
	    return true;
	} else if (!m_softLimitOverridden && elapsed > m_softLimit) {
	    if (fractionComplete > 0.6) {
		// If we're significantly more than half way by the
		// time we reach the soft limit, ignore it (though
		// always respect the hard limit, above). Otherwise
		// respect the soft limit and report out of time now.
		m_softLimitOverridden = true;
	    } else {
		return true;
	    }
	}

	return false;
    }

private:
    std::chrono::time_point<std::chrono::steady_clock> m_start;
    bool m_haveLimits;
    double m_minFraction;
    double m_softLimit;
    double m_hardLimit;
    bool m_softLimitOverridden;
};

#endif