Before I do anything, I want your opinions on implementation. The items needed to do this are:

• let my_color:Color = fltk::enums::Color::from_html("#ffffff"); Similar to the from_rgb() method
• callback() is color popup that replaces current widget color. Are callbacks possible with this? Especially being able to do set_label(string_html_value_returned_from_static_function)
• pub FlColor(pub String); // Same convention

If it is simple to make callbacks function here, I would like to also make other common dialogs, like FlFile(String) to open a file chooser. It would also simply set_label() as well. Perhaps a checkbox button with fl_ask() Using something like FlAsk(pub value:bool, pub label:String); Can a callback set the struct fields?

// from the docs
but.set_callback(move |_| frame.set_label("Hello World!")); // the closure capture is mutable borrow to our button

I know this is likely fringe, but is this even possible?

#[derive( Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
#[cfg_attr(feature = "fltkform", derive(FltkForm))]
pub struct Config<T:Copy 
                 + Default
                 + AddAssign
                 + Add<Output = T>
                 + Div<Output = T>
                 + DivAssign
                 + Mul<Output = T>
                 + MulAssign
                 + Neg<Output = T>
                 + Rem<Output = T>
                 + RemAssign
                 + Sub<Output = T>
                 + SubAssign
                 + std::cmp::PartialOrd> {
    /// Identification Number
    pub id:T,
    pub cost:T,
    pub amount:T,
}

A struct within a struct causes a crash and backtrace is required to decipher nested structs do not work. That said, nested enums, etc... work

The other issue is internal sizing, as you mentioned:

I think scaling the size of label is more important than the 'input', and unless something changed in FLTK you need to calculate text width by yourself. I've done it in the past based on the font size, but did not find the best solution.

All in all this is great!!! What an easy way to make a GUI for entering info!!! I can now build a GUI prefilled with values and switch between files with hardly any coding! This is so amazing!!

To sub nest a struct, the only possible way i can think is to return an Fl_Tab, with a Group for each extra struct as a tab. If every internal struct became a tab, it could potentially create a ton of tabs, and tabs within Tabs. But AFAIK this should nest correctly and look okay.

This has me wanting to get into macros, you are really good at this stuff!! Thanks so much!

Or is there a way to quickly theme all elements inside a Group that would make this redundant? Is this type of thing accessible using *_prop_()? Thanks again for doing this!