[pdf-devel] Re: GNU PDF functions

[Hardy Falk]

address@hidden wrote:
> Ok, besides the interpolation functions, what more do we need?
>
> - Streams (containing the samples or the postscript function
>   definitions) will be provided in the second layer of the library
>   (the object layer).
>
> - The dictionary structure containing the function attributes will
>   also be provided in the object layer.
>
> - The interpreter for postscript functions.. well, AFAIK the pdf
>   functions are the unique part of the codebase where that facility is
>   used. Then we could implement it in the document layer where the
>   notion of "pdf function" is introduced.
>
> What do you think?


Hmm, I think that most of my confusion arises from the following 
observation:
The PDF reference describes the lexical (syntactic) structure of a
pdf function object, along with the desired effects of function application.

The pdf_obj_t type has strong ties to its lexical representation.
It is not callable, though.

My old implementation uses a  pdf_func_t type.
A call to pdf_eval_func( pdf_func_t, pdf_real_t in[], pdf_real_t out[])
can evaluate any pdf function in a uniform way.

Strangely enough, this highly specialized type seems to belong to the 
base layer. Its internals reflect the description in section 3.9, with 
emphasis on function application only. It is not a pdf object, and it 
does not use pdf objects. The object layer would provide
a conversion constructor from  pdf_obj_t to pdf_func_t.
The base layer would handle cleanup and deallocation.

What's your opinion?