Two Krita technical questions

JL VT pentalis at
Tue Jun 22 15:30:02 CEST 2010

First of all sorry if the questions had obvious answers, they're not
so obvious to me!.

Question(s) one, for the Scratch Off algorithm:
I have a paintop, and want to store image data in a place where: 1.-
it is invisible to the user  2.- survives the destruction and
reinvocation of the paintop.
std::clog tells me that paintops are created when the user presses
down the mouse button, and destroyed when he releases it. That leads
me to think that anything I create inside the paintop won't survive
till the next creation-destruction cycle, but maybe I'm missing
I want to know: how can I achieve (1) and (2)?. If there's a place in
the code where someone does something similar, just point me to that
file, I can learn from it. Or tell me what classes to use or roughly
what's the principle of what to do with them (i.e.: if you use this,
it will survive the paintop destruction, just be sure to erase it when
you stop using it or it will leak memory).
If there's more than one way to do it(tm), please point me to the most
"orthodox" or most "desirable" way to do it. I already refactored my
code and prefer to keep it clean and shiny.

Question(s) two, for general hatching:
I have a hatching KisBrushBasedPaintOp. I have a nice BrushTip
dialogue, that gives me a bitmap with a pre-made dab.
What I don't have is an idea of how to use that dab as a transparency
mask for my hatching.
My idea is to first hatch a little paint device just like I'm doing
now --let's call it "DabHatch"--, then to access the mask stored in
m_brush (the one we customize in the BrushTip popup dialogue) --let's
call it "DabMask"--, and use it to determine the transparency of
pixels in "DabHatch", creating a new image ready to be potato-stamped
on the image, let's call it "DabHappiness". The creation of
DabHappiness should follow these rules:
--Assume opacity can be represented with a number ranging from 0 to 1,
where 0 is "transparent" and 1 is "opaque". Then...
--opacity_of_pixels_in_DabHappiness = opacity_of_pixels_in_DabHatch *
How can I do that?, is there a command?, an easily accessible method?.
Please, just like in the last question, point me to a file where it is
done if it is already done in a file; otherwise show me the principle
and the classes used to do it, and let me know what's the most
"orthodox" and "desirable" way to do it.

Thank you very much for your time.

PS: I assumed Lukas wouldn't want answers like this to go to waste so
I went forward and asked here for the answer to be publicly stored  :]

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