[gl2ps] Translate pixels to points

[Pantxo Diribarne]

Le 27/10/2016 à 10:26, Pantxo Diribarne a écrit :
>
>
>
>>             I'd like to come back to this discussion in regard to the
>>             discrepancy between SVG and EPS output size: from a
>>             M-by-N *pixels* opengl viewport, gl2ps draws a M-by-N
>>             *points* figure for EPS format and a M-by-N *pixels*
>>             figure for SVG format.
>>             I think one of those should be fixed.
>>
>>             As I said in the beginning of the discussion, I'd vote
>>             for introducing a new "resolution" (default 72 pixels per
>>             inch) argument for gl2psBeginPage. This would provide a
>>             way to translate screen coordinates into whatever units
>>             we like in gl2ps.
>>
>>             Pantxo
>
>             I like your suggestion. That would simplify things. Are
>             you working on a patch?
>
>             Since "points" has a different meaning for Linux, Windows
>             (96 ppi), and Mac (72 ppi), should the default change with
>             os? Or is the ppi always 72 for pdf?
>
>             Ben
>
>
>         Why does the screen resolution (hardware+software) have to be
>         OS specific (pure software)?
>
>         As for the patch, I'd like to hear opinions before going
>         ahead. In particular the approach I propose will change the
>         signature of gl2psBeginPage which will force every user to
>         change their code. Another less invasive option would be
>         adding a "gl2psScreenResolution" function. The drawback is
>         that such parameter has no reason to be changed in the middle
>         of a drawing so having it fixed from the start seems more
>         consistent.
>
>         Pantxo
>
>
>     Ben, now I think I understand what you meant. Actually it is
>     "pixel" that have a different meaning for different systems: some
>     use screen(physical) pixels (linux) and others use device
>     independent pixels (Mac).
>     E.g in Mac carbon API if you request a 10-by-10 pixels window you
>     will obtain a 20-by-20 physical pixels window on retina (HDPI)
>     screens. This is untrue for the opengl API which always works with
>     physical pixels. See e.g.
>     http://blog.qt.io/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/
>     <http://blog.qt.io/blog/2013/04/25/retina-display-support-for-mac-os-ios-and-x11/>
>
>     This tells us that a "resolution" argument should be expressed in
>     physical(screen)-pixels per inch.
>
>     Pantxo
>
>
> I went ahead and produced a patch (see attached). I chose the invasive 
> approach (adding an argument to gl2psBeginPage) since the resolution 
> must be known at the very beginning of the process.
>
> Pantxo
>
>

Did someone have time to test/look at the patch? Does this feature have 
a chance to make it into gl2ps? Should it be reworked so that it doesn't 
break the API?

Thanks in advance for your time.


Pantxo

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