annotate base/ScaleTickIntervals.h @ 1418:e7cb4fb2aee4 scale-ticks

Rework log scale calculation, update to changed interface

/* -*- 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 2006-2017 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 SV_SCALE_TICK_INTERVALS_H
#define SV_SCALE_TICK_INTERVALS_H

#include <string>
#include <vector>
#include <cmath>

#define DEBUG_SCALE_TICK_INTERVALS 1

#ifdef DEBUG_SCALE_TICK_INTERVALS
#include <iostream>
#endif

#include "LogRange.h"

class ScaleTickIntervals
{
public:
    struct Range {
	double min;        // start of value range
	double max;        // end of value range
	int n;             // number of divisions (approximate only)
    };

    struct Tick {
	double value;      // value this tick represents
	std::string label; // value as written 
    };

    typedef std::vector<Tick> Ticks;

    /**
     * Return a set of ticks that divide the range r linearly into
     * roughly r.n equal divisions, in such a way as to yield
     * reasonably human-readable labels.
     */
    static Ticks linear(Range r) {
        return linearTicks(r);
    }

    /**
     * Return a set of ticks that divide the range r into roughly r.n
     * logarithmic divisions, in such a way as to yield reasonably
     * human-readable labels.
     */
    static Ticks logarithmic(Range r) {
        LogRange::mapRange(r.min, r.max);
        return logarithmicAlready(r);
    }

    /**
     * Return a set of ticks that divide the range r into roughly r.n
     * logarithmic divisions, on the asssumption that r.min and r.max
     * already represent the logarithms of the boundary values rather
     * than the values themselves.
     */
    static Ticks logarithmicAlready(Range r) {
        return logTicks(r);
    }
    
private:
    enum Display {
        Fixed,
        Scientific,
        Auto
    };
    
    struct Instruction {
	double initial;    // value of first tick
        double limit;      // max from original range
	double spacing;    // increment between ticks
	double roundTo;    // what all displayed values should be rounded to
	Display display;   // whether to use fixed precision (%e, %f, or %g)
	int precision;     // number of dp (%f) or sf (%e)
        bool logUnmap;     // true if values represent logs of display values
    };
    
    static Instruction linearInstruction(Range r)
    {
        Display display = Auto;

	if (r.max < r.min) {
	    return linearInstruction({ r.max, r.min, r.n });
	}
	if (r.n < 1 || r.max == r.min) {
            return { r.min, r.min, 1.0, r.min, display, 1, false };
        }
	
	double inc = (r.max - r.min) / r.n;

        double digInc = log10(inc);
        double digMax = log10(fabs(r.max));
        double digMin = log10(fabs(r.min));

        int precInc = int(floor(digInc));
	double roundTo = pow(10.0, precInc);

        if (precInc > -4 && precInc < 4) {
            display = Fixed;
        } else if ((digMax >= -2.0 && digMax <= 3.0) &&
                   (digMin >= -3.0 && digMin <= 3.0)) {
            display = Fixed;
        } else {
            display = Scientific;
        }
        
        int precRange = int(ceil(digMax - digInc));

        int prec = 1;
        
        if (display == Fixed) {
            if (digInc < 0) {
                prec = -precInc;
            } else {
                prec = 0;
            }
        } else {
            prec = precRange;
        }

#ifdef DEBUG_SCALE_TICK_INTERVALS
        std::cerr << "\nmin = " << r.min << ", max = " << r.max << ", n = " << r.n
                  << ", inc = " << inc << std::endl;
        std::cerr << "digMax = " << digMax << ", digInc = " << digInc
                  << std::endl;
        std::cerr << "display = " << display << ", inc = " << inc
                  << ", precInc = " << precInc << ", precRange = " << precRange
                  << ", prec = " << prec << std::endl;
        std::cerr << "roundTo = " << roundTo << std::endl;
#endif

        double min = r.min;
        
        if (roundTo != 0.0) {
            inc = round(inc / roundTo) * roundTo;
            if (inc < roundTo) inc = roundTo;
            min = ceil(min / roundTo) * roundTo;
            if (min > r.max) min = r.max;
        }

        if (display == Scientific && min != 0.0) {
            double digNewMin = log10(fabs(min));
            if (digNewMin < digInc) {
                prec = int(ceil(digMax - digNewMin));
#ifdef DEBUG_SCALE_TICK_INTERVALS
                std::cerr << "min is smaller than increment, adjusting prec to "
                          << prec << std::endl;
#endif
            }
        }
        
        return { min, r.max, inc, roundTo, display, prec, false };
    }
    
    static Instruction logInstruction(Range r)
    {
        Display display = Auto;

	if (r.n < 1) {
	    return {};
	}
	if (r.max < r.min) {
	    return logInstruction({ r.max, r.min, r.n });
	}
        if (r.max == r.min) {
            return { r.min, r.max, 1.0, r.min, display, 1, true };
        }
	
	double inc = (r.max - r.min) / r.n;

        double digInc = log10(inc);
        int precInc = int(floor(digInc));
	double roundTo = pow(10.0, precInc);

        if (roundTo != 0.0) {
            inc = round(inc / roundTo) * roundTo;
            if (inc < roundTo) inc = roundTo;
        }

        // if inc is close to giving us powers of two, nudge it
        if (fabs(inc - 0.301) < 0.01) {
            inc = log10(2.0);
        }

        // smallest increment as displayed
        double minDispInc =
            LogRange::unmap(r.min + inc) - LogRange::unmap(r.min);

        int prec = 1;

        if (minDispInc > 0.0) {
            prec = int(floor(log10(minDispInc)));
            if (prec < 0) prec = -prec;
        }

        if (r.max >= -2.0 && r.max <= 3.0 &&
            r.min >= -3.0 && r.min <= 3.0) {
            display = Fixed;
            if (prec == 0) prec = 1;
        }
        
#ifdef DEBUG_SCALE_TICK_INTERVALS
        std::cerr << "\nmin = " << r.min << ", max = " << r.max << ", n = " << r.n
                  << ", inc = " << inc << ", minDispInc = " << minDispInc
                  << ", digInc = " << digInc << std::endl;
        std::cerr << "display = " << display << ", inc = " << inc
                  << ", precInc = " << precInc
                  << ", prec = " << prec << std::endl;
        std::cerr << "roundTo = " << roundTo << std::endl;
#endif
        
	double min = r.min;
        if (inc != 0.0) {
            min = ceil(r.min / inc) * inc;
            if (min > r.max) min = r.max;
        }

        return { min, r.max, inc, 0.0, display, prec, true };
    }

    static Ticks linearTicks(Range r) {
        Instruction instruction = linearInstruction(r);
        Ticks ticks = explode(instruction);
        return ticks;
    }

    static Ticks logTicks(Range r) {
        Instruction instruction = logInstruction(r);
        Ticks ticks = explode(instruction);
        return ticks;
    }
    
    static Tick makeTick(Display display, int precision, double value) {
        const int buflen = 40;
        char buffer[buflen];
        snprintf(buffer, buflen,
                 display == Auto ? "%.*g" :
                 display == Fixed ? "%.*f" :
                 "%.*e",
                 precision, value);
        return Tick({ value, std::string(buffer) });
    }
    
    static Ticks explode(Instruction instruction) {

#ifdef DEBUG_SCALE_TICK_INTERVALS
	std::cerr << "initial = " << instruction.initial
                  << ", limit = " << instruction.limit
                  << ", spacing = " << instruction.spacing
		  << ", roundTo = " << instruction.roundTo
                  << ", display = " << instruction.display
		  << ", precision = " << instruction.precision
                  << ", logUnmap = " << instruction.logUnmap
                  << std::endl;
#endif

        if (instruction.spacing == 0.0) {
            return {};
        }

        double eps = 1e-7;
        if (instruction.spacing < eps * 10.0) {
            eps = instruction.spacing / 10.0;
        }

        double max = instruction.limit;
        int n = 0;

        Ticks ticks;
        
        while (true) {
            double value = instruction.initial + n * instruction.spacing;
            if (value >= max + eps) {
                break;
            }
            if (instruction.logUnmap) {
                value = pow(10.0, value);
            }
            if (instruction.roundTo != 0.0) {
                value = instruction.roundTo * round(value / instruction.roundTo);
            }
	    ticks.push_back(makeTick(instruction.display,
                                     instruction.precision,
                                     value));
            ++n;
	}

        return ticks;
    }
};

#endif