CairoGauge.hh

/* CairoGauge.hh - Gtk::DrawingArea-based analog gauge widget
 *
 * Copyright (C) Javier Lopez-Gomez, 2016
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#ifndef CAIROGAUGE_HH
#define CAIROGAUGE_HH

#include <cairomm/context.h>
#include <cmath>
#include <functional>
#include <gtkmm.h>
#include <string>

class CairoGauge : public Gtk::DrawingArea {
protected:
  // TODO: make this a configurable parameter
  /// The default font size for this widget
  static constexpr unsigned CAIROGAUGE_FONT_SIZE = 14;

  typedef std::function<double(void *)> sample_fn_t;

  std::string _text;
  sample_fn_t _sample_fn;
  double _value, _value_max, _tick_step;
  size_t _label_step;
  Cairo::Matrix _transform_matrix;
  Cairo::RefPtr<Cairo::Surface> _background;

  void draw_background(void);

  bool on_draw(const Cairo::RefPtr<Cairo::Context> &context) override;
  void on_size_allocate(Gtk::Allocation &allocation);

public:
  /** Construct a CairoGauge object
   * @param text Text rendered below the gauge
   * @param fn std::function<double(void *)> that returns the next value
   * @param _M Maximum value of any sample
   * @param step Draw ticks using @a step increments
   * @param l_step Draw labels each @a l_step ticks
   */
  CairoGauge(std::string text, sample_fn_t fn, double _M, double step = 0, size_t l_step = 1)
      : _text(text), _sample_fn(fn), _value(0), _value_max(_M), _tick_step(step), _label_step(l_step),
        _transform_matrix(Cairo::identity_matrix()) {}
  CairoGauge(const CairoGauge &_o)
      : CairoGauge(_o._text, _o._sample_fn, _o._value_max, _o._tick_step, _o._label_step) {}
  virtual ~CairoGauge() {}

  void set_transform_matrix(Cairo::Matrix &_m) {
    _transform_matrix = _m;
    queue_draw();
  }

  /** Call the @a fn function (constructor argument) and update gauge with
   * the returned value.
   */
  void update(void *arg);

protected:
  double angle_of(double value) { return 5 * M_PI_4 - (value / _value_max * 3 * M_PI_2); }
};

#endif /* CAIROGAUGE_HH */