Re: 'with pixels' (was Re: Engines are started; ...)

[Ethan A M. <merritt@u.washington.edu>]

Hans-Bernhard Broeker <br...@ph...> wrote:
> Ethan A Merritt wrote:
> > The code in datafile.c and elsewhere (df_readline is not so much
> > the culprit here) makes an assumption that it can deduce the style of
> > plot based on the number of input columns requested.
>
> Could you show a concrete example of that?

The worst offenders are one level up, in plot[23]d.c in the routines
get_data and get_3ddata.  Each of these contains a huge switch
statement that controls the interpretation of input data columns
based on the total number of returned columns.  Within each
'case <ncols>:' of the switch statement, the code then tries to
run through all possible plot modes that could have generated
that number of input columns. I think this is an example of the tail
wagging the dog;  the main switch statement should rather be
over the plot types.

The problematic code in df_readline() itself is the bit which decides
where to stuff the input values based on the number of requested input
columns. It allows for an implicit x coordinate value, but only in the
case of 'plot ... using <y> with <something that only takes 2 cols>' 

  /* FIXME EAM - Trap special case of only a single 'using' column. */
  /* But really we need to handle general case of implicit column 0 */
        if (output == 1)
            xpos = (axcol == 0) ? df_datum : v[axcol-1];
        else
            xpos = v[axcol];


I even have a real-life example of why this sort of assumption is limiting 
our options.   I would have liked to allow the new 'splot with labels' style
to accept the same sort of pm3d coloring options that other plotting
styles offer.  But I gave up trying to work around the assumptions in the
current code that if you have a color value at all, then it must be in the
4th input column.  'splot with labels' needs the 4th specified input
column to be the label itself; if there were an additional color value it
would be in an optional 5th input column.  Yeah, I could hack this to
work somehow, but it would be a whole lot easier if the code were
organized based on plot style rather than on number of columns. 


-- 
Ethan A Merritt
Department of Biochemistry & Biomolecular Structure Center
University of Washington, Seattle