On 07.06.2011 17:30, Paul R wrote: > I think am kind of getting this.. the idea is derive a class from fl widget, > so then my own class which say calls an fl_box into being > can then use the box as it's 'drawing canvas' by calling the inherited > draw function from the widget class.
It is difficult to understand what you mean with "my own class which say calls an fl_box into being". Real code would be much easier to understand (for me). > Whenever i wanted to draw the rectangle i could just call > myClass.draw(x,y,w,h) ?? You mean "object_of_myclass.draw(x,y,w,h)? Again, this may seem to be nitpicking, but how to explain something (or say "yes, this is right") if you don't know what the OP really wanted to say? I'll try with my own words... The main problem you must consider before you ask how and when you can call some drawing functions is how all GUIs behave in general. _One_ aspect is: you must always be able to draw the entire window when needed, e.g. because it has been obscured by another window. This can also be true only for a part of your window. FLTK manages an important part for you: it discovers if and when a part of your window needs drawing and calls the draw() methods of all widgets in the window that need drawing. Before it calls the individual draw() methods, it will set up the internal OS drawing context so that all drawing functions can draw into the right window. Now, if you derive your class from Fl_Box, then yes, you can use this box as a drawing canvas to do point, line, and rectangle drawing as you like. But you must keep in mind that you must always draw the entire widget, because it can be reset to an empty background whenever the surrounding (parent) Fl_Group or Fl_Window are drawn. At least you must be able to draw the entire widget, if draw() is called by FLTK. Note that the box() type of your widget can even be FL_NO_BOX, so that no background will be drawn, if you want that. But if you derived your own draw() method, then you must call a box drawing method anyway if you want to have a defined background; otherwise your widget will be transparent, as Greg noted already in his reply. If you want to draw some points or lines (like an oscilloscope) at arbitrary times, then you *can* [1] do it e.g. in a timer callback, but this is somewhat "volatile", unless you also save all the data you need to draw also somewhere in the widget's memory so that you can replicate it at any point in time (when FLTK calls the draw() method of your widget). Usually it is much easier to store the data in the widget and call redraw() so that FLTK *will* call draw() for you at the right time and after preparing the drawing context. This can be improved if you flag the parts that need updates with damage() calls or in the widget's memory and set up the clipping area to avoid flicker, but that's OT here. [1] If you *really* want to draw on-the-fly data into an existing widget, then you can call Fl_Window::make_current() to set up the drawing context, but this is *not* recommended. Read the comment on make_current() in the docs at http://www.fltk.org/doc-1.3/classFl__Window.html about what is called "incremental update". HTH Albrecht _______________________________________________ fltk mailing list [email protected] http://lists.easysw.com/mailman/listinfo/fltk
