Re: [Sketch-devel] transparent bitmaps

[David B. <da...@sl...>]

On Thursday 18 Apr 2002 8:42 pm, Bernhard Herzog wrote:

> David Boddie <da...@sl...> writes:

> > I may have broken gradient fills in my copy.
>
> What exactly is wrong? There may well be a bug that for some reason
> doesn't show on my system.

When I apply a gradient fill, the object becomes unfilled. Maybe I should
check out a clean copy of the CVS tree and try that.

> > I did glance at the PDF specification, but didn't notice anything which
> > mentioned the method used for transparency. There was something about
> > using a key colour for transparent pixels, but it wasn't really relevant.
>
> It's in the PDF 1.4 spec, chapter 7. Earlier versions didn't have
> transparency.

I'll take a look.

I've reimplemented translucency using alpha values which are stored
separately to the image. I created an SKAlphaObject like the SKColorObject
already present, but I'm wondering whether I can just use a float instead.

My main worries are to do with extending the various fills in
Sketch/Graphics/pattern.py to use alpha blending.

I have changed the __init__ method of SolidPattern, for example, to

    def __init__(self, color = None, duplicate = None, alpha = None):

and introduced an skeloader.py filter which calls SolidPattern with
the named alpha parameter where appropriate. This works with the
HatchingPattern, too.

Is it a good idea to add named parameters to these methods?

David

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