Re: pngcairo: suggestion for additional option

[Allin C. <cot...@wf...>]

On Fri, 28 Dec 2007, Ethan A Merritt wrote:

> Allin:
> 
> I attach a revised version of your patch.
> The changes are:
> - Export pre-calculated values for TERM_XMIN etc taken from the axis
>   structures
> - Initialize term->tscale to 1.0 for all terminals that do not provide
>   an explicit value
> - Initialize term->tscale for SVG terminal
> 
> Please give it a look-over.  

This looks good to me.  It works fine for the various PNG plots 
that I've checked.

> Also please help me figure out which other terminals need an 
> explicit scale, and whether the exported variables need to be of 
> type double rather than integer. For instance, I think "post 
> eps" needs a scale factor of 20, but PostScript coordinates are 
> not limited to integers.  A test plot gave
>         TERM_XMIN = 546
>         TERM_XMAX = 6990
>         TERM_YMIN = 280
>         TERM_YMAX = 4872
> and dividing back by 20 will give non-integral values.  I am also worried
> that to actually use these values we would also need to have the offset
> of the coordinate origin relative to the origin of the PostScript page.
> On the other hand, the necessary information is already in the output
> PostScript file, so perhaps it is not necessary to export it as a user
> variable inside gnuplot.  What do you think?

I see what you mean about PostScript.  I find that TERM_XMIN et al 
agree with a readback from the mouse in gv, if I divide by 20 
(that is, 2*PS_SC) and add the coordinates of the bottom left of 
the bounding box -- that is, (50,50).  I also see that division by 
the scale factor of 20 yields non-integral values, but I'd think 
that for practical purposes having these measurements to the 
nearest PostScript point would probably be sufficient.

As for the translation of the bounding box: yes, it's quite easily 
readable from the PostScript file.  I'm not sure whether a user 
would want/expect the measurements net or gross of the PostScript 
translation; I think it might be enough to state somewhere that
they are net.

-- 
Allin Cottrell
Department of Economics
Wake Forest University, NC