Re: {png,pdf}cairo terminals and font size

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

On Wednesday 09 September 2009, Allin Cottrell wrote:
> 
> I like the *cairo terminals a lot: PNG looks good on screen and
> PDF is good for publication-quality output; and these two
> terminals share a common command-set with high fidelity, since
> they use a common back-end.  Except for one thing...
> 
> The help for both pngcairo and pdfcairo says that the default size
> for fonts is 6 points.  That's fine, and if you go with the
> default you get quite consistent-looking output from the two
> terminals.
> 
> But if you alter the size, an inconsistency emerges.  Suppose I'd
> prefer 8 points.  I do my PNG plot using
> 
> set term pngcairo font ",8"
> 
> then do my PDF plot using
> 
> set term pdfcairo font ",8"
> 
> Relative to the "6-point" baseline, the PNG file shows a smaller
> font (8 < 6, hmm) while the PDF plot shows a larger font (8 > 6).
> 
> I'm happy to take a look at the code and see if I can come up with
> a patch for this.  But I'd rather hear any comments first.

I don't see anything immediately in looking at the code.
It really is initialized to 6, but after that it seems to just pass
through any request to the cairo library.

The whole idea of "font size" in a png image is kind of arbitrary anyhow,
since it depends entirely on the pixel size of the device it is viewed on.
Perhaps there is some "pixels per inch" setting in the cairo context that
can be tweaked? 

	Ethan