Re: [Lib2geom-devel] some todos and wishes

[mgsloan <mg...@gm...>]

Hmm, I think i may not have sent it to the lists...

After playing a bit with the library, I came up with some todos and
> wishes, that I submit before I forget them; some might already be there
> but I was not aware, or some might be bad ideas for some other reason...
> These are just suggestions:
>
> First, things would be more pleasant if we had:
> - automatic conversions: sb to pw<sb> (Linear to sb, double to Linear).
> - allow +,-,* between double,sb,pw<sb>,d2<pw<sb>>,d2<pw<sb>>.
> - allow composition sb(pw<sb>)
> - allow composition d2<pw<sb>>(sb) and pw<d2<sb>>(sb)
> - define a plotter function for d2<pw<sb>> and pw<d2<sb>> (for toys/tests)
>


Sounds good!  There's at least an explicit constructor for sb -> pw<sb>, and
I know there is a Linear -> SBasis.  I think I have an accidental double ->
Linear too.  Turns out single parameter constructors are interpreted as
conversions!  At somepoint I'll probably switch the single param
constructors over to explicit conversions, and stick explicit on all
non-conversion constructors.

One thing I'd like to avoid is too many operators.  Often times when it
can't figure out what you mean by a particular operator, it'll print out all
of the declerations associated with it.  However, we certainly want a
complete, predictable set of operations across all.  It's possible we might
be able to leverage implicit conversion to minimize operator numbers.

As far as the plotters, cairo_md_sb can handle D2<Piecewise<SBasis> >.
Actually, Piecewise<D2<SBasis> > would be loads easier to implement - will
do next time.

Some remarks about our conventions:
> - define "bridges" between d2<pw<sb>> and pw<d2<sb>>.
>   Although d2<pw<sb>> is usefull in some situations (plotting a function
>   for instance), many operations require synchronous cuts, so pw<d2<sb>>
>   instead. Note that once a d2<pw<sb>> has synchronous cuts, there is no
>   synchronizing for each new operation... To make this implicit, our
>   functions should accept both d2<pw<sb>> and pw<d2<sb>>, and do some
>   conversion if needed. Or should we get rid of d2<pw<sb>>?


I actually think pw<d2<sb>> might be a good way to handle that.  currently
i've got a sectionize function that does d2<pw<sb>> -> vector<d2<sb>> but
that's not very good.  pw<d2<sb>> would be a much better output for it.

- fix convention about empty sb/pw<sb>: an empty sb is the constant 0
>   while empty pw<sb> are not allowed. How do we represent 0 in pw<sb>
>   world? as (pw<sb>)Linear(0)?


The thing is, either way there's going to be a check.  I suppose the good
thing about disallowing it is that it doesn't matter what the function
actually does.  The current convention is that it is indeed constant zero,
but i suppose concat does need a bit of work in that respect.  Yes, that's
the main way to reasonably represent 0.

Some less relevant todos:
> - define some standard functions for pw<sb>: sqrt, cos, sin...
> - define pw<sb> and d2<pw<sb>> bounds.


Sounds good.  yeah, I never really put much time into d2, more of a copy
paste and modify of multidim

What do you think?


some good ideas!