Re: Proposal: Saving graphs from Qt and wxt terminals

[Philipp K. J. <ja...@ie...>]

On Sat, 25 Oct 2014 16:09:49 -0400 (EDT)
Allin Cottrell <cot...@wf...> wrote:

> On Fri, 24 Oct 2014, Philipp K. Janert wrote:
> 
> >> One thing to be careful of is the fact that saving to PDF (which is
> >> certainly welcome in my opinion because the first word of PDF means
> >> "portable") in the Qt terminal isn't using the PDF terminal.  There
> >> are no colors in the PDF output via Qt, whereas the PDF terminal
> >> creates a PDF output with colors.  Do we want as setup in which the
> >> interactive terminals use the PDF terminal, or a setup in which the
> >> interactive terminals use their own custom PDF output?
> >
> > I thought one could use the native APIs of the
> > rendering library to handle the transformation
> > to the desired graphics format (in the spirit
> > of pngcairo and pdfcairo - both rendered, similarly,
> > using the same lib). I think Qt can do that, too.
> 
> The cairo library can generate PDF, EPS, SVG or PNG at will, but only 
> given a suitable abstract description of the plot. No library can 
> transform a graphic from a bitmap format such as PNG to a "proper"
> vector representation.

Yes, I realize that. 

I guess the question then becomes: in what form is
the graph information is available "when the button 
is pressed".

Not knowing the code, I could guess that what is 
copied to the clipboard (currently) is only the
already-rendered bitmap. No way to construct a
meaningful vector graphic from that!

The implication seems to be that the "save as file"
GUI event would have to interact more deeply with
gnuplot's internals: it actually has to go back, get
the data set (and all that) and recreate the plot,
basically from scratch, just using a different backend.

That's different and more complicated than saving an
already rendered bitmap to the clipboard. I had not 
appreciated that difficulty sufficiently! (Too bad.)

> 
> Consider just fonts, for example: a proper vector file contains the 
> specification of the fonts used so they can be reproduced at any 
> resolution. A bitmap contains no real font information, just the
> pixels that compose the glyphs in the plot at a given, fixed
> resolution.
> 
> Allin Cottrell
> 
>