[GRASS-user] translucency and svg output

[Vincent Bain]

Pete, sorry if I'm off board :
do you absolutely need to generate a /vector/ output ?

Vincent.

Le mercredi 24 mars 2010 à 20:15 -0700, pete davidson a écrit :
> On Wed, Mar 24, 2010 at 7:49 PM, pete davidson <caitifty at gmail.com>
> wrote:
>         
>         
>         
>         On Wed, Mar 24, 2010 at 7:42 PM, Glynn Clements
>         <glynn at gclements.plus.com> wrote:
>                 
>                 pete davidson wrote:
>                 
>                 > I'm producing maps in svg format using the cairo
>                 driver and d.out.file.  One
>                 > thing I'd really like to be able to do is set one or
>                 more of the vector
>                 > layers to be partially translucent.  After rummaging
>                 through this list, I'm
>                 > beginning to wonder if its possible at all, since
>                 translucency in the guis
>                 > seems to be handled by g.pnmcomp, but perhaps
>                 someone with more experience
>                 > knows a way to do it.
>                 
>                 
>                 It isn't. The graphics API doesn't support an alpha
>                 component.
>                 
>                 Apart from anything else, it can't easily be
>                 implemented for
>                 PostScript output, as PostScript doesn't support
>                 translucency. Faking
>                 it with patterns is possible, but it starts getting
>                 complicated if you
>                 want more than one translucent layer.
>                 
>                 > The only workaround I've managed to find so far is
>                 to export each layer as
>                 > an individual svg, then use something like inkscape
>                 to rejoin them, setting
>                 > the translucency/transparency of each layer as I do
>                 it.  Which is fine for a
>                 > map with only a few layers, but gets tedious when
>                 dealing with maps with
>                 > dozens of layers.
>                 
>                 
>                 SVG is XML, so it shouldn't be especially hard to
>                 automate the process
>                 using generic XML-processing tools.
>         
>         Ohh, I hadn't thought of editing the svg/xml directly.  Thanks
>         for the suggestion, I'll see what I can achieve from there.
>         
> 
> And then we discover that the 'svg' produced by cairo using the above
> script is actually just a png in an svg wrapper..  At least for my
> particular install of Grass.  That's frustrating.  Ahh well, back to
> the drawing board.
> 
> Peter
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