Inheriting Fl_Dial gotchas

[pvr...@btinternet.com]

I found the hard way that when overriding the draw and handle methods of Fl_Dial (actually Fl_Line_Dial) i could only effectively inherit the draw() and handle(int event) metods and not those which supplied the position and size values. The documentation inferred that the draw(X,Y,W,H) and equivalent handle methods were available for sub-classes. I took this to mean they could be overridden.

Thanks Phil.

[Matthias Melcher]

The documentation shows, which functions are `virtual`. C++ is relatively limited in comparison to other languages. In Java, everything is virtual, and Lua goes even further, for example.

https://www.fltk.org/doc-1.4/classFl__Widget.html

You can of course still call all non-private methods. So, to achieve overriding draw(x, y, w, h), you override draw() instead and get the coordinates using Fl_Widget::x(), y(), w(), and h().

The original Dial code does just that:

void Fl_Dial::draw() {

  draw(x(), y(), w(), h());

  draw_label();

}