Re: key text placement in SVG

[<pl...@pi...>]

On 10/12/12 19:34, Ethan A Merritt wrote:
> On Thursday, October 11, 2012 12:42:22 pm Allin Cottrell wrote:
>> I'm comparing the output of gnuplot's svg and pngcairo
>> drivers, with a thought of making greater use of SVG. But
>> there seems to be a slight problem with the placement of key
>> text in the SVG output. Here's a little test script
>>
>> set term svg font "Sans,8" size 680,400
>> set output 'test.svg'
>> set key left top
>> plot sin(x) title "PRIME" w l, cos(x) title "UNEMP" w l
>>
>> In the PNG version the key is just fine, but in SVG the "U" of
>> "UNEMP" gets tangled up with the y-axis (more or less,
>> depending on the magnification). I'm looking at the SVG using
>> librsvg, and also via the Adobe NPSVG3 library. To show what
>> I'm talking about,
>
>> I'm attaching the SVG output as converted to PNG by rsvg-convert
>> (at 96dpi).
>    ^^^^^^^^^^
>
> That dpi setting turns out to be relevant.
> I went back to the SVG spec and learned the following:
>
> - you can specify font-size in either absolute or relative units
>
> - font-size="8pt" requests an 8 point font regardless of the
>    display resolution or current scaling.  That's what gnuplot does.
>    In theory, if you view an SVG document in a viewer that allows
>    you to rescale the figure, the font should display as the same
>    size even after rescaling the plot.  That is, if you shrink the
>    figure the font does _not_ shrink with it.

Not what I am finding in practise. I have a gnuplot graph in svg which 
contains text formatted as follows:

<g transform="translate(41.3,43.7)" style="stroke:none; fill:black; 
font-family:verdana; font-size:9.00pt; text-anchor:end">

Both Opera and FF zoom both the text and graph lines with the zoom 
feature (if that is what you were referring to by rescale).

Frankly , that is what I would expect.  Like if I zoom an html document, 
the main reason would be to increase the rendition of the font size.

Maybe I misunderstood "rescale".

/Peter.



>
> - font-size="8" or font-size="8px" requests a font size relative to
>    the current display units.  It will scale up or down as the figure
>    is re-sized.
>
> - For a 95dpi display, 8pt is translated to 10px.  That is, it is
>    displayed 25% larger than gnuplot was expecting.  This is probably
>    at the heart of the problem.
>
> - You can confirm this by opening the output of your test command in
>    inkscape and then saving it to a new *.svg file.  The original gnuplot
>    output contains text marked "font-size:8pt" but inkscape converts this
>    to "font-size:10"  (no units).
>
> I don't know what is the best thing to do here.
> Being able to specify an absolute font size makes sense in many
> cases, but not in all cases.  Perhaps we need a gnuplot terminal option
> that controls whether gnuplot writes out absolute or relative units for
> the font size.  I suppose the code that estimates text length would have
> to be aware of this also.
>
> 	Ethan
>
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