On Tue, 11 Mar 2003 09:46:49 +0000
"Adam D. Moss" <[EMAIL PROTECTED]> wrote:

> The idea
> of rehash-on-dirty would be to catch identical tiles, even
> accidentally-identical tiles (like great masses of transparent
> tiles, presuming that you scrub the RGB data of a transparent
> pixel; the row-hints stuff has been doing this and potentially
> breaking the ill-advised anti-erase feature for 100 years now
> and no-one has complained)

Perhaps because no-one knew, you should not have told us this.

I think that the user should be able to edit the alpha channel independent
from the other channels. I don't think that it is unreasonable that a user
initially makes some parts of the layer transparent, then makes some other
edits to the layer and finally decides that the transparency boundaries
should be slightly different, e.g. slightly more feathered. In most cases
this will work fine but when some of the tiles have been scrubbed this
will not work for these tiles. 

In my mental model the alpha information is simply one of the "color"
channels, that are all completely independent from one another. What I
find particularly nasty is that scrubbing could happen at unexpected
moments and this makes it very difficult to reproduce any bugs that are
related to this "feature".

If it is really desirable to remove color information from transparent
pixels, this must have a predictable behavior. The logical place seems to
be the operations that modify the alpha channel, e.g. erase. These
operations should set the color channels to 0 for transparent pixels. In
this way you get at least reproducable behavior.

Finally, when everybody believes that scrubbing by the tile manager is a
great idea, I have another one: delete all tiles from the image that are
completely obscured by higher layers. After all, like the color
information in transparent pixels, these tiles do not contribute anything
to the final image, so it seems very reasonable delete them. Also I
suggest that a good random number generator is used to decide when these
tiles are deleted :)


Ernst Lippe
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