// drawing.cxx (example4)

#include <FL/Fl.H>
#include <FL/Fl_Window.h>
#include <FL/Fl_Slider.h>
#include <FL/Fl_Button.h>
#include <FL/Fl_Int_Input.h>
#include <FL/Fl_draw.h>

#include <cstdio>
#include <cmath>

class ShapeWidget : public Fl_Widget {

private:

  int sides_;

  void draw();

public:

  int sides() const;
  void sides(int n);

  ShapeWidget(int x,int y,int w,int h,const char *l=0);

};

ShapeWidget::ShapeWidget(int x,int y,int w,int h,const char *l) :
  Fl_Widget(x,y,w,h,l), 
  sides_(3) 
{
}

void ShapeWidget::draw() {
    fl_color(FL_BLACK);
    fl_rectf(x(),y(),w(),h());
    fl_push_matrix();
    fl_scale(w()/2.0, h()/2.0);
    fl_translate(1+(2.0*x())/w(),1+(2.0*y())/h());
    fl_color(0x8098b000);
	fl_begin_complex_polygon();
    for (int i=0; i<sides(); i++) {
      double ang = i*4*acos(0)/sides();
      fl_vertex(cosf(ang),sinf(ang));
    }
	fl_end_complex_polygon();
    fl_color(FL_WHITE);
	fl_begin_line();
    for (int i=0; i<=sides(); i++) {
      double ang = i*4*acos(0)/sides();
      fl_vertex(cosf(ang),sinf(ang));
    }
	fl_end_line();
    fl_pop_matrix();
    fl_font(labelfont(), labelsize());
    //fl_color(FL_WHITE);
    char buf[200];
    double ang = 4*acos(0)/sides();
    snprintf(buf, 200,
             "%d sides\n"
             "Angle between sides = %g\n"
             "Length of side = %g\n"
             "Perimiter = %g\n"
             "Area = %g",
             sides(),
             360.0/sides(),
             sqrt(2-2*cos(ang)),
             sides()*sqrt(2-2*cos(ang)),
             sides()*sin(ang)/2);
    fl_draw(buf, x(), y(), w(), h(), FL_ALIGN_WRAP);
}

int ShapeWidget::sides() const {
  return sides_;
}

void ShapeWidget::sides(int n) {
  if (sides_ != n) {
    sides_ = n; 
	redraw();
  }
}

static void slider_callback(Fl_Widget* widget, void* data) {
  ((ShapeWidget*)data)->sides(int(((Fl_Slider*)widget)->value()));
}

int main( ) {

  Fl_Window window(300, 330);
  window.begin();

  ShapeWidget sw(10, 10, 280, 280);
  window.resizable(&sw);

  Fl_Slider slider(50, 295, window.w()-60, 30, "Sides:");
  slider.type(FL_HORIZONTAL);
  slider.align(FL_ALIGN_LEFT);
  slider.callback(slider_callback, &sw);
  slider.value(sw.sides());
  slider.step(1);
  slider.range(3,40);

  window.end();
  window.show();
    
  return Fl::run();
}