How to draw multiple rectangles FLTK C++ - c++

Question

I am trying to create a program in fltk and I followed this example
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
int main(int argc, char **argv) {
Fl_Window *window = new Fl_Window(340,180);
Fl_Box *box = new Fl_Box(20,40,300,100,"Hello, World!");
box->box(FL_UP_BOX);
box->labelfont(FL_BOLD+FL_ITALIC);
box->labelsize(36);
box->labeltype(FL_SHADOW_LABEL);
window->end();
window->show(argc, argv);
return Fl::run();
}
from FLTK docs. The problem is I'm trying to draw multiple rectangle shapes to the window and it seem very tedious to create multiple boxed in order to have multiple rectangles. I tried looking up a lot of tutorials on drawing shapes on FLTK but I can't find anything simple enough to show me.
My code looks like this so far
#include <FL/Fl.H>
#include <FL/Fl_Widget.H>
#include <FL/Fl_Window.H>
// #include <FL/fl_draw.H>
#include <iostream>
int main() {
Fl_Window *window = new Fl_Window(900, 600);
window->position(0, 0);
window->color(FL_BLACK);
window->end();
window->show();
while (1) {
int ev = Fl::event();
if (ev == FL_SHORTCUT) {
if (Fl::event_key() == FL_Escape)
break;
}
Fl::check();
}
return 0;
}
and I would like to implement the drawing inside the loop (continuously).

Answer 1

As an important side note: You should really consider using Fl::run() instead of your custom while loop, I ran into many problems with a similar approach like yours.
Now, to answer your question:
Take the example and wrap the Box creation inside a loop. You can take for example an index for assigning different positions to each Box.
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
int main(int argc, char **argv) {
Fl_Window *window = new Fl_Window(340,500);
// 3 Fl_Boxes in a loop
for (int i = 0; i < 3; ++i) {
Fl_Box *box = new Fl_Box(20, 40 + i*120, 300, 100,"Hello, World!");
box->box(FL_UP_BOX);
box->labelfont(FL_BOLD+FL_ITALIC);
box->labelsize(36);
box->labeltype(FL_SHADOW_LABEL);
}
window->end();
window->show(argc, argv);
return Fl::run();
}
You control the layout with the formula 20, 40 + i*120, 300, 100 in the box Constructor. You have to adjust that to your requirements.
With FLTK one basic rule is: All widgets you initialize between the window constructor and window->end() or any other widget that works the same way, for example Fl_Group, will become children of the surrounding element and will show, if their parent is shown.
I am not entirely sure, if Fl_Box is what you are looking for. I found Erco's FLTK Cheat Page extremely helpful. You might find inspiration and other approaches to your problem there.