Re: Transparancy

[Bernhard Herzog]

Antoon Pardon <address@hidden> writes:

> A few months ago, the idea of somekind of
> transparant colors was mentioned here.
> (colors which let the color under them
> influence how they look like.)
>
> I was just wondering how far the authors of
> skencil want to go with this idea (on the
> long term.)

There is already some code for it in CVS :) thanks to David Boddie. If
you open an image with alpha channel it will be drawn with transparency.

I have some more code that I haven't got around to check in yet that
adds some basic user interface support for it. Once that's checked in
there will be support for a fill-opacity setting for objects that can be
filled. It only applies to uniform fills at the moment, though and only
the libart renderer actually supports it. It can not be printed or
exported in any way yet (only written to .sk files).


> I am especially curious if those transparant
> colors are to be usable in hatchings and
> gradients.

I think it's best to follow SVG for a start. A possible roadmap could
be:

1. Images with transparency (already done)

2. fill opacity. This is mostly done for uniform fills, but not
   completely in CVS yet. Has yet to be implemented for other fill types

3. stroke opacity. This should be easy as we only support uniform colors
   anyway at the moment.

4. Object opacity. This is a bit tricky since an object can have all of
   object opacity, fill opacity and stroke opacity which interact in
   ways that can make it impossible to just draw everything into one
   bitmap. Also, in SVG object opacity can be applied to groups which
   currently don't have graphics properties in Skencil

5. Opacity settings for gradient stops (I think SVG has this)

 ... not sure which next and maybe 5 should be done before 4.

For hatchings we should probably have two opacity values, one for the
stroked lines and one for the gap, although I'm not sure how exactly
they should interact.

All of this has to be implemented for printing and export, of course.
Nothing has been done about that so far (although I think there are some
patches from David for the drawfile filters).

Another question is how much of this should be in 0.8 (or whatever we
call the stable series after 0.7 -- there are some advantages to calling
it 1.0). I think having fill and stroke opacity is feasible as not much
is missing, depending on how much support we want for it in the
import/export filters and printing.

   Bernhard

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