Problems with "embedded" transparency masks onto adj. layers

[Boudewijn Rempt]

On Thursday 10 September 2009, Dmitry Kazakov wrote:
> On Thu, Sep 10, 2009 at 12:06 PM, Boudewijn Rempt <boud at valdyas.org> wrote:
> > On Wednesday 09 September 2009, Dmitry Kazakov wrote:
> > > In current realization we get wrong result - we just copy alpha()
> > > channel
> >
> > It might be instead of a bug in Krita a bug in the alpha colorspace's
> > implementation of the OVER composite op. That looks like it has changed
> > since
> > 1.6. I'll investigate that a bit.
> 
> First, current realization does NOT use COMPOSITE_OVER by default. It uses
> COMPOSITE_ALPHA_DARKEN instead [0].
> I don't know why (and it still looks quite strange for me) but Cyrille said
> ALPHA_DARKEN "is more beautiful". I can't say anything about that.

Only when using indirect painting, which is not applicable to selections. 

> Even if we decide to use COMPOSITE_OVER, it won't solve the problem at all.
> Before drawing on canvas dab of the brush will be converted to alpha8()
> automaticaly by pigment. It means that dab will loose(!) all it's color
> information and only brush's alpha-mask will be used as a source of
> painting. More than that, the bitBlt WON'T have any useful alpha mask to
> control painting (as a colorspace has only one channel and it is used as a
> source of bitBlt). This means that whole rectangle will be painted onto the
> canvas and any composition type is simply _not applicable_ here(!) as we do
> not have useful alpha mask for painting.

Please, do me a favour and check out 1.6. You'll see that the selection brush 
paints on selections, and it doesn't paint squares. We've got a bug here, but 
I still don't believe in an enormous design issue.

> It's not "a change from 1.6". Painting on the selection simply hadn't been
> planned in the design of classes.

Em, the fact remains that in 1.6, painting on selections was perfectly 
possible, and that I had designed selections and the selection brush tool in 
1.6 to make it possible to paint on.

> And the fact that IndirectPainting simply CAN'T be applied to selections
> speaks for that.

Indirect painting has only one goal to avoid making the brush stroke darker 
when you go over a spot several times in the same stroke. That isn't very 
relevant for selections.

-- 
Boudewijn Rempt | http://www.valdyas.org