annotate layer/ColourScale.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 file copyright 2006-2016 Chris Cannam and QMUL.
    
    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 COLOUR_SCALE_H
#define COLOUR_SCALE_H

#include "ColourMapper.h"

enum class ColourScaleType {
    Linear,
    Meter,
    Log,
    Phase,
    PlusMinusOne,
    Absolute
};

/**
 * Map values within a range onto a set of colours, with a given
 * distribution (linear, log etc) and optional colourmap rotation.
 */
class ColourScale
{
public:
    struct Parameters {
	Parameters() : colourMap(0), scale(ColourScaleType::Linear),
		       minValue(0.0), maxValue(1.0),
		       threshold(0.0), gain(1.0) { }

	/** A colour map index as used by ColourMapper */
	int colourMap;
	
	/** Distribution for the scale */
	ColourScaleType scale;
	
	/** Minimum value in source range */
	double minValue;
	
	/** Maximum value in source range. Must be > minValue */
	double maxValue;

	/** Threshold below which every value is mapped to background
	    pixel 0 */
	double threshold;

	/** Gain to apply before clamping and mapping */
	double gain;
    };
    
    /**
     * Create a ColourScale with the given parameters.
     *
     * Note that some parameters may be ignored for some scale
     * distribution settings. For example, min and max are ignored for
     * PlusMinusOneScale and PhaseColourScale and threshold and gain
     * are ignored for PhaseColourScale.
     */
    ColourScale(Parameters parameters);
    ~ColourScale();

    ColourScale(const ColourScale &) = default;
    ColourScale &operator=(const ColourScale &) = default;

    /**
     * Return the general type of scale this is.
     */
    ColourScaleType getScale() const;
    
    /**
     * Return a pixel number (in the range 0-255 inclusive)
     * corresponding to the given value.  The pixel 0 is used only for
     * values below the threshold supplied in the constructor. All
     * other values are mapped onto the range 1-255.
     */
    int getPixel(double value) const;

    /**
     * Return the colour for the given pixel number (which must be in
     * the range 0-255). The pixel 0 is always the background
     * colour. Other pixels are mapped taking into account the given
     * colourmap rotation (which is also a value in the range 0-255).
     */
    QColor getColourForPixel(int pixel, int rotation) const;
    
    /**
     * Return the colour corresponding to the given value. This is
     * equivalent to getColourForPixel(getPixel(value), rotation).
     */
    QColor getColour(double value, int rotation) const {
	return getColourForPixel(getPixel(value), rotation);
    }

private:
    Parameters m_params;
    ColourMapper m_mapper;
    double m_mappedMin;
    double m_mappedMax;
    static int m_maxPixel;
};

#endif