Filter processor

The pdf_filter_processor is an example of a processor that allows chaining. PDF operators are fed into the processor, which then `filters' them and passes them out to another processor.

$\begin{lstlisting} /* pdf_new_filter_processor: Create a filter processor. This... ...ctx, pdf_processor *chain, pdf_obj *old_res, pdf_obj *new_res); \end{lstlisting}$

Similar filtering processors could be written for other tasks, such as discarding all the text from a page, changing all occurrences of a particular font for another, or converting all the objects on a page to a given colorspace.

The component parts of this processor are generally functions named pdf_filter_....