Sven Neumann wrote:
You will however notice that GIMP instead needs 8 bytes per
pixel. In addition to the 3 bpp for the RGB layer it allocates a
projection the size of the image. This projection holds the result of
compositing the layer stack. It is always allocated 4 bpp. Additionally
a selection mask is allocated which adds another byte per pixel.
(As an aside, once upon a time, we did have such a thing as
greyscale projections.)
So what could be done to improve this? We could for example try to get
around the need for a projection for the case where people are working
with a single layer only. Instead of displaying from the projection,
we could display directly from the layer.
I think we used to do this, too. At least, I struggled for a
long time making the projection tiles be initialised to a lazy
copy-on-write reference to the bottom layer (IIRC the tile hinting
system would also preserve these cheap refs even when there
were multiple layers where the upper layers were largely
transparent). There were some annoying corner cases (duplicating
a zoomed-in image) which I now don't remember if we ever got
right. :(
But it still seems like the elegant way to do this (erk, but it
probably did rely on the projection being able to assume the
same depth as the image).
It might also help to allocate the selection lazily. That is to not
allocate the tiles at all until the selection mask is altered. This
might actually happen already, I am not sure about it.
Not sure. Might be able to do this elegantly (elegance again being
in the eye of the beholder) by initialising all of the selection
tiles to a COW of the same 'blank' tile (and doing the same in
the 'clear selection' operation, etc).
--Adam
--
Adam D. Moss . ,,^^ adam@xxxxxxxx http://www.foxbox.org/ co:3
