Thank you so much! It seemed that I have to provide the sourcecode of the
modified fltk and link the my own code(close-code) against the modified version
of fltk statically. And is there any other mehtod to implement a modified
version of Fl_Text_Display , such as subclassing as usual without copying code?
In this example, what I want to modify is only a single method (not virtual
function) of Fl_Text_Display.
It will be a tedious work to implement the other part of Fl_Text_Display in my
own way.
Thanks again.
> DISCLAIMER: I'm not a license specialist, and my reply is in no way
> authoritative, but I hope it may help...
>
> Sparkaround wrote:
>
> > If I create a widget Test_Text_Display which is subclassed from
> > Fl_Text_Display, will it constitute a derivative work as fltk's Software
> > License?
>
> Subclassing, as it is usually done, is not a derivative work in
> FLTK's licensing.
>
> However, copying code is generally not allowed, otherwise it *will*
> be a derivative work, and IMHO all the (L)GPL rules apply (your own
> code will also need the (L)GPL license).
>
> However, see below...
>
> > The implementation of Test_Text_Display may like this:
> > class My_Text:public My_Text_Display
> > {
> > public:
> > ...
> > void draw();//modified
> > void draw_string(...);//modified
>
> This (above) may be problematic.
>
> > void old_draw(...);//only copy code
> > void draw_text(...);//only copy code
> > void draw_vline(...);//only copy code
>
> Don't *copy* code (see below).
>
> > ...
> > };
> >
> > void Test_Text_Display::draw()
> > {
> > ...
> > old_draw();
> > ...
> > }
>
> No problem, if "..." is your own code.
> old_draw() could be replaced with Fl_Text_Display::draw().
>
> > void Test_Text_Display::old_draw()
> > {
> > //full copy of Fl_Text_Display::draw() in Fl_Text_Display.cxx
> > }
>
> Don't do that. You don't need old_draw(), because you can call
> Fl_Text_Display::draw() as mentioned above.
>
> > void Test_Text_Display::draw_text()
> > {
> > //full copy of Fl_Text_Display::draw_text().
> > //The same code as the one in Fl_Text_Display.cxx.
> > }
> > void Test_Text_Display::draw_vline(...)
> > {
> > //full copy from fltk's source code without modification as above
> > }
>
> You don't need this. It's there already by inheritance.
>
> > void Test_Text_Display::draw_string(...)
> > {
> > //part of copy of the original Fl_Text_Display::draw_string(...).
> > //Do some modification, such as remove "clear_rect"
> > ...
> > }
> >
> > That is to say, draw_string() was modified based on the original one in
> > Fl_Text_Display.cxx , and all functions that call draw_string from the
> > original draw() was copied from Fl_Text_display to Test_Text_Display
> > without modification.
>
> That would IMHO classify your code as a derivative work. You copied
> and modified FLTK code. But there is maybe another way.
>
> > I noticed that there is an exception in fltk's Software License:
> > "2.Widgets that are subclassed from FLTK widgets do not constitute a
> > derivative work."
> >
> > Does implementation of Test_Text_Display like above constitute a
> > derivative work?
>
> IMHO, yes.
>
> However, again IMHO(!), you could also modify the FLTK library itself
> and link your application with this modified library. In this case
> you would have to provide the FLTK source code modifications to your
> users (or customers), but the modified library would still be LGPL.
> Then you can link your application with this modified library.
>
> But again, I'm not a license specialist and not a lawyer. This may well
> be wrong.
>
> Albrecht
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