Re: [Matplotlib-users] path effects question

[Damon M. <dam...@gm...>]

On Sat, Jul 14, 2012 at 04:09:48PM -0400, Benjamin Root wrote:
> On Saturday, July 14, 2012, John Hunter wrote:
> 
> >
> >
> > On Sat, Jul 14, 2012 at 11:48 AM, John Hunter <jd...@gm...<javascript:_e({}, 'cvml', 'jd...@gm...');>
> > > wrote:
> >
> >> I do not understand why in the following example, if I set
> >> patch_alpha=1.0, I do not see the shadow effect.  I would expect to see it
> >> for the the rightmost four bars, where the original bars do not entirely
> >> occlude the shadow, so even if alpha is 1.0, there are parts of the shadow
> >> that are not behind the original bars and should still be visible.
> >>
> >>
> >>
> >
> > I now see that this line explains the behavior
> >
> >
> > https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/patheffects.py#L183
> >
> >  gc0.set_alpha(1.-self._patch_alpha)
> >
> > so maybe I should amend my question: is this desirable that the shadow
> > alpha is 1-patch_alpha, since an alpha of 1 on the patch does not imply
> > that there is no visible shadow?
> >
> >
> 
> I would argue that the shadow's alpha should equal the patch's alpha.  The
> more opaque the patch, the less light that should get through.  Could there

I am inclined to agree here. Should it instead be:

gc0.set_alpha(self._patch_alpha)?

> have been an alpha blending reason for this?
> 
> Ben Root


-- 
Damon McDougall
http://damon-is-a-geek.com
B2.39
Mathematics Institute
University of Warwick
Coventry
West Midlands
CV4 7AL
United Kingdom