'Re: Grayscale Selections'

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List: kde-kimageshop
Subject: Re: Grayscale Selections
From: Dmitry Kazakov <dimula73 () gmail ! com>
Date: 2011-06-25 10:18:59
Message-ID: BANLkTinN1d0MPH1LoQ4G3aG2UN1_hegbxQ () mail ! gmail ! com
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> as you may have seen I have started a new branch
> krita-selection-grayscale-langkamp with some experiments around grayscale
> masks. Dmitry wanted to have a mail to show what I'm doing.
>
> So for now I have changed pixel and vector selection to use a grayscale
> with no alpha channel instead of the current alpha colorspace. I have also
> fixed the marching ants to work with that.
>
> The biggest problem currently is that in most parts we assume the
> non-selected parts to be transparent. Now the default pixel of the selection
> isn't transparent anymore which means that extent() will fallback to use
> KisDefaultBounds and often return an pratically infinite rect. I'm think
> about adding a parameter to extent() and the other methods to optionally not
> use default bounds here.
>

KisDefaultBounds returns infinite rect, because it is not connected to any
image. So it has no source to read bounds from. The image pointer should be
given to the constructor of the paint device.
I don't think adding a parameter will make things better. I guess it'll make
the things even worse. Because in such a case you will not be able to
process any selection having defaultPixel() not completely black. An
example: after a select all call we can create a selection with default
pixel equal to white (opaque); the real extent() of such device will be
empty rect. But the extent for the processing -- image->bounds(). So as a
solution I think the best way is to tell the colorspace to return
alpha()==grayChannel(). In such a way the defaultBounds mechanism would be
activated and all non-transparent pixels would be processed.

Pros:
+ this approach fit the general idea filters use: we guarantee the image
processed right inside image bounds only.
+ the callers should not bother about the default pixel of the selection
Cons:
- in case we try to merge two selections it doesn't change the default pixel

Well yes, we can add a separate method like
rectThatDoesntChangeWhenYouChangeTheDefaultPixel() (and we actually do
already have such a method [1]), but in such a case, could you define all
the cases when we should use this method and when we should not?

Defining the usecases for it is quite important, because usage of such
method automatically makes the person to deal with the default pixel of the
device manually.

-- 
Dmitry Kazakov

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<div class="gmail_quote"><blockquote class="gmail_quote" style="margin: 0pt 0pt \
0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">as you may \
have seen I have started a new branch krita-selection-grayscale-langkamp with some \
experiments around grayscale masks. Dmitry wanted to have a mail to show what I&#39;m \
doing. So for now I have changed pixel and vector selection to use a \
grayscale with no alpha channel instead of the current alpha colorspace. I have also \
fixed the marching ants to work with that. The biggest problem currently is \
that in most parts we assume the non-selected parts to be transparent. Now the \
default pixel of the selection isn&#39;t transparent anymore which means that \
extent() will fallback to use KisDefaultBounds and often return an pratically \
infinite rect. I&#39;m think about adding a parameter to extent() and the other \
methods to optionally not use default bounds here. </blockquote><div> KisDefaultBounds returns infinite rect, because it \
is not connected to any image. So it has no source to read bounds from. The image \
pointer should be given to the constructor of the paint device. I don&#39;t think \
adding a parameter will make things better. I guess it&#39;ll make the things even \
worse. Because in such a case you will not be able to process any selection having \
defaultPixel() not completely black. An example: after a select all call we can \
create a selection with default pixel equal to white (opaque); the real extent() of \
such device will be empty rect. But the extent for the processing -- \
image-&gt;bounds(). So as a solution I think the best way is to tell the colorspace \
to return alpha()==grayChannel(). In such a way the defaultBounds mechanism would be \
activated and all non-transparent pixels would be processed. Pros: + this \
approach fit the general idea filters use: we guarantee the image processed right \
inside image bounds only. + the callers should not bother about the default pixel \
of the selection Cons: - in case we try to merge two selections it doesn&#39;t \
change the default pixel Well yes, we can add a separate method like \
rectThatDoesntChangeWhenYouChangeTheDefaultPixel() (and we actually do already have \
such a method [1]), but in such a case, could you define all the cases when we should \
use this method and when we should not? Defining the usecases for it is quite \
important, because usage of such method automatically makes the person to deal with \
the default pixel of the device manually. </div></div> -- Dmitry \
Kazakov

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