Re: [matplotlib-devel] Re: backend change needed: render patch without boundary

Darren,

Thanks.  I expect that a slight modification of your patch will fit in 
perfectly with what I have in mind, and it is particularly helpful 
because I know next to zip about svg--and about most of the other 
backend output formats.

I think you misunderstood what I was suggesting; it was not that alpha 
would be zero in the svg output, but rather that the backend would use 
alpha==0 in the line color (or gc.alpha) as a flag to not output the 
stroke command, in the same way as I started using linewidth for this. 
In the same way, alpha==0 in the facecolor would turn off output of the 
fill command.  So, even if you start with svg and then go to postscript, 
the result should be correct.

It is all a little kludgy.  Some things use rgb, some use rgba; some 
alpha values are ignored completely.  The GraphicsContextBase has alpha 
but GraphicsContextPS does not.  The gc seems to have *almost* all the 
information that gets passed down to the lowest-level renderer 
functions, but lacks the face color; etc.  A more thorough rewrite could 
clean up a lot of things, but as John noted it would require 
simultaneously modifying the entire set of backends. Instead, my 
intention is to make small changes that move towards a greater degree of 
consistency but without breaking anything. This does not preclude a more 
extensive refactoring in the future; if anything, it should facilitate it.

Eric

Darren Dale wrote:
> On Saturday 27 May 2006 09:06, Darren Dale wrote:
> 
>>On Saturday 27 May 2006 04:29, Eric Firing wrote:
>>
>>>Darren noticed that because of the edge-drawing problem, ps and svg
>>>backends were making unusable colorbars for image-type plots, so I put a
>>>quick hack into the ps backend to make it work until the more general
>>>solution is put into place.
>>
>>Thank you for doing that. I need to use the svg backend to make plots for
>>my poster. I was thinking about how to change the svg backend, and setting
>>the alpha to zero may create a problem. For example, I create an svg file
>>with mpl, and import it into inkscape. Then I print the document to my
>>postscript printer, which does not support alpha, and therefore some
>>unexpected lines show up on the printed page. Its a corner case, but I bet
>>a fair number of people will get nailed by it.
> 
> 
> Here's a hack that works for me:
> 
> $ svn diff
> Index: lib/matplotlib/backends/backend_svg.py
> ===================================================================
> --- lib/matplotlib/backends/backend_svg.py      (revision 2417)
> +++ lib/matplotlib/backends/backend_svg.py      (working copy)
> @@ -71,20 +71,25 @@
>          else:
>              dashes = 'stroke-dasharray: %s; stroke-dashoffset: %f;' % (
>                  ' '.join(['%f'%val for val in seq]), offset)
> +
> +        linewidth = gc.get_linewidth()
> +        if linewidth:
> +            return 'style="fill: %s; stroke: %s; stroke-width: %f; ' \
> +                'stroke-linejoin: %s; stroke-linecap: %s; %s opacity: %f; ' \
> +                '%s"' % (fill,
> +                         rgb2hex(gc.get_rgb()),
> +                         linewidth,
> +                         gc.get_joinstyle(),
> +                         _capstyle_d[gc.get_capstyle()],
> +                         dashes,
> +                         gc.get_alpha(),
> +                         clippath,)
> +        else:
> +            return 'style="fill: %s; opacity: %f; ' \
> +                '%s"' % (fill,
> +                         gc.get_alpha(),
> +                         clippath,)
> 
> -        return 'style="fill: %s; stroke: %s; stroke-width: %f; ' \
> -               'stroke-linejoin: %s; stroke-linecap: %s; %s opacity: %f; ' \
> -               '%s"' % (
> -                   fill,
> -                   rgb2hex(gc.get_rgb()),
> -                   gc.get_linewidth(),
> -                   gc.get_joinstyle(),
> -                   _capstyle_d[gc.get_capstyle()],
> -                   dashes,
> -                   gc.get_alpha(),
> -                   clippath,
> -                   )
> -
>      def _get_gc_clip_svg(self, gc):
>          cliprect = gc.get_clip_rectangle()
>          if cliprect is None:
> @@ -144,10 +149,10 @@
>          y = self.height-y-h
>          im.write_png(filename)
> 
> -       imfile = file (filename, 'r')
> -       image64 = base64.b64encode (imfile.read())
> -       imfile.close()
> -       os.remove(filename)
> +        imfile = file (filename, 'r')
> +        image64 = base64.b64encode (imfile.read())
> +        imfile.close()
> +        os.remove(filename)
>          lines = [image64[i:i+76] for i in range(0, len(image64), 76)]
> 
>          self._svgwriter.write (
> 
> 
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