CairoGauge.cc

/* CairoGauge.cc - 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.
 */

#include "CairoGauge.hh"

void CairoGauge::draw_background(void) {
  const int width = get_allocation().get_width(), height = get_allocation().get_height(),
            radius = std::min(width, height) / 2;
  size_t j = 0;
  Cairo::TextExtents TE;

  _background = get_window()->create_similar_surface(Cairo::CONTENT_COLOR_ALPHA, width, height);
  auto context = Cairo::Context::create(_background);

  // setup
  context->set_antialias(Cairo::ANTIALIAS_SUBPIXEL);
  context->translate(width / 2, height / 2);
  context->set_line_cap(Cairo::LINE_CAP_ROUND);
  context->set_line_width(2);
  context->set_font_size(CAIROGAUGE_FONT_SIZE);
  Gdk::Cairo::set_source_rgba(context, get_style_context()->get_color(Gtk::STATE_FLAG_NORMAL));

  context->arc_negative(0, 0, 0.8 * radius, M_PI_4, 3 * M_PI_4);
  context->stroke();
  if (_tick_step != 0)
    for (double i = 0, _r1 = 0.78 * radius, _r2 = 0.82 * radius, _r3 = 0.9 * radius; i <= _value_max;
         i += _tick_step, j++) {
      double angle = angle_of(i);
      std::string label = std::to_string(static_cast<int>(i));
      bool is_labeled = (j % _label_step) == 0;
      double _r4 = is_labeled ? (_r1 * 0.95f) : _r1;

      context->move_to(_r4 * cos(angle), _r4 * -sin(angle));
      context->line_to(_r2 * cos(angle), _r2 * -sin(angle));
      context->stroke();

      if (is_labeled) {
        context->get_text_extents(label, TE);
        context->move_to((_r3 * cos(angle)) - TE.width / 2, _r3 * -sin(angle));
        context->show_text(label);
      }
    }
  context->get_text_extents(_text, TE);
  context->move_to(-TE.width / 2, 0.7 * radius);
  context->show_text(_text);
}

bool CairoGauge::on_draw(const Cairo::RefPtr<Cairo::Context> &context) {
  const int width = get_allocation().get_width(), height = get_allocation().get_height(),
            radius = std::min(width, height) / 2;

  context->set_antialias(Cairo::ANTIALIAS_SUBPIXEL);
  context->translate(width / 2, height / 2);
  context->transform(_transform_matrix);
  context->set_line_cap(Cairo::LINE_CAP_ROUND);

  if (!_background)
    draw_background();
  context->set_source(_background, -width / 2, -height / 2);
  context->paint();

  // draw needle
  double angle = angle_of(_value);
  context->set_line_width(3);
  context->set_source_rgba(1, 0.2, 0.2, 1);
  context->move_to(0, 0);
  context->line_to(0.76 * radius * cos(angle), -0.76 * radius * sin(angle));
  context->stroke();
  context->arc(0, 0, 0.03 * radius, 0, 2 * M_PI);
  context->fill();

  return TRUE;
}

void CairoGauge::on_size_allocate(Gtk::Allocation &allocation) {
  Gtk::Widget::on_size_allocate(allocation);
  if (_background)
    draw_background();
}

void CairoGauge::update(void *arg) {
  auto v = _sample_fn(arg);
  if (v != _value) {
    _value = v;
    get_window()->invalidate_rect(Gdk::Rectangle(0, 0, get_allocation().get_width(), get_allocation().get_height()),
                                  FALSE);
  }
}