view base/ScaleTickIntervals.h @ 1407:25ed6dde2ce0 scale-ticks

Scale tick labeller, and tests (some failing so far)

/* -*- 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>

#include <iostream>


class ScaleTickIntervals
{
public:
    struct Range {
	double min;        // start of value range
	double max;        // end of value range
	int n;             // number of divisions requested (will be n+1 ticks)
    };

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

    struct Ticks {
	double initial;    // value of first tick
	double spacing;    // increment between ticks
	double roundTo;    // what all displayed values should be rounded to
	bool fixed;        // whether to use fixed precision (%f rather than %e)
	int precision;     // number of dp (%f) or sf (%e)
	std::vector<Tick> ticks;  // computed tick values and labels
    };
    
    static Ticks linear(Range r) {

	if (r.n < 1) {
	    return {};
	}
	if (r.max < r.min) {
	    return linear({ r.max, r.min, r.n });
	}
	
	double inc = (r.max - r.min) / r.n;
	if (inc == 0) {
	    Ticks t { r.min, 1.0, r.min, false, 1, {} };
	    explode(r, t);
	    return t;
	}
	
	double ilg = log10(inc);
	int prec = int((ilg > 0.0) ? round(ilg) : trunc(ilg)) - 1;
	int dp = 0, sf = 0;
	bool fixed = false;
	if (prec < 0) {
	    dp = -prec;
	    sf = 1; // was 2, but should probably vary
	} else {
	    sf = prec;
	}
	if (sf == 0) {
	    sf = 1;
	}
	if (prec > -4 && prec < 4) {
	    fixed = true;
	}

	double roundTo = pow(10.0, prec);
	inc = round(inc / roundTo) * roundTo;
	double min = ceil(r.min / roundTo) * roundTo;
	if (min > r.max) min = r.max;

	Ticks t { min, inc, roundTo, fixed, fixed ? dp : sf, {} };
	explode(r, t);
	return t;
    }

private:
    static void explode(const Range &r, Ticks &t) {
	std::cerr << "initial = " << t.initial << ", spacing = " << t.spacing
		  << ", roundTo = " << t.roundTo << ", fixed = " << t.fixed
		  << ", precision = " << t.precision << std::endl;
	auto makeTick = [&](double value) {
	    const int buflen = 40;
	    char buffer[buflen];
	    snprintf(buffer, buflen,
		     t.fixed ? "%.*f" : "%.*e",
		     t.precision, value);
	    return Tick({ value, std::string(buffer) });
	};
	for (double value = t.initial; value <= r.max; value += t.spacing) {
	    value = t.roundTo * round(value / t.roundTo);
	    t.ticks.push_back(makeTick(value));
	}
    }
};

#endif