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

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

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/base/ScaleTickIntervals.h	Wed May 03 13:02:08 2017 +0100
@@ -0,0 +1,112 @@
+/* -*- 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