C++ fltk — Theming (Flutter)

Table of contents

#include <FL/Enumerations.H>
#include <FL/Fl.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Button.H>
#include <FL/Fl_Window.H>
#include <FL/fl_draw.H>

#include <functional>
#include <iostream>

#define WIDTH 600
#define HEIGHT 400
#define BLUE fl_rgb_color(0x42, 0xA5, 0xF5)
#define SEL_BLUE fl_rgb_color(0x21, 0x96, 0xF3)
#define GRAY fl_rgb_color(0x75, 0x75, 0x75)
#define LIGHT_GRAY fl_rgb_color(211, 211, 211)

using cb_t = std::function<void(Fl_Widget *)>;

class MyBox : public Fl_Box {
 public:
  MyBox(int x, int y, int w, int h, const char *title = NULL)
      : Fl_Box(x, y, w, h, title) {}
  virtual void draw() override {
    fl_rectf(0, h(), w(), 3, LIGHT_GRAY);
    Fl_Box::draw();
  }
};

template <typename T>
class WidgetWrapper : public T {
  cb_t func_ = NULL;

 public:
  WidgetWrapper(int x, int y, int w, int h, const char *title = NULL)
      : T(x, y, w, h, title) {}
  void set_cb(cb_t &&func) {
    func_ = func;
    auto cb = [](Fl_Widget *w, void *data) {
      auto fn = *static_cast<cb_t *>(data);
      fn(w);
    };
    this->callback(cb, &func_);
  }
};

int main() {
  auto win = new Fl_Window(WIDTH, HEIGHT, "Flutter-like");
  auto bar = new WidgetWrapper<MyBox>(0, 0, WIDTH, 60, "    FLTK APP");
  bar->align(FL_ALIGN_LEFT | FL_ALIGN_INSIDE);
  auto txt = new WidgetWrapper<Fl_Box>(
      250, 180, 100, 40, "You have pushed the button this many times:");
  auto count = new WidgetWrapper<Fl_Box>(txt->x(), txt->y() + 40, 100, 40, "0");
  auto but = new WidgetWrapper<Fl_Button>(WIDTH - 100, HEIGHT - 100, 60, 60,
                                          "@+6plus");
  win->end();
  win->show();

  // theming
  Fl::background(255, 255, 255);
  Fl::visible_focus(false);

  bar->box(FL_FLAT_BOX);
  bar->labelsize(22);
  bar->labelcolor(FL_WHITE);
  bar->color(BLUE);

  txt->labelsize(18);
  txt->labelfont(FL_TIMES);

  count->labelsize(36);
  count->labelcolor(GRAY);

  but->color(BLUE);
  but->selection_color(SEL_BLUE);
  but->labelcolor(FL_WHITE);
  but->box(FL_OFLAT_BOX);
  // end theming

  but->set_cb([=]([[maybe_unused]] Fl_Widget *b) {
    std::cout << "Lambda callback called" << std::endl;
    auto label = atoi(count->label());
    label += 1;
    char buf[12];
    (void)snprintf(buf, 12, "%d", label);
    count->copy_label(buf);
  });

  return Fl::run();
}

Possible output

Lambda callback called
Lambda callback called
Lambda callback called

References

• title
• title
• title