(soz if you get this multiple times, it hasn't turned up after ~24h) Sven Neumann wrote:
looks very sane overall and I couldn't find any obvious design mistakes. There is one thing that is already halfway implemented in
*cough* - completely implemented IIRC in respect to what it was originally intended for. :)
the current system and that I'd like to see considered. I'm speaking of a way to have hints about the pixel data stored in tiles. Such a hint could for example state that the tile is completely transparent, that it is fully opaque or even solid-colored. We have this as tile-row hints since GIMP-1.2 but I think it would make sense to have such hints on the tile level as well. The cache system should probably know about these hints since it wouldn't make much sense to swap a solid-colored tile to disk since it can be regenerated faster than it could be swapped in.
It's a reasonable direction, I think, but I have two comments: * It probably makes sense to detect whether a whole tile is transparent/solid/etc just-in-time when you're about to consider swapping it out (or dropping it down to a colder cache) instead of every time it gets dirty. IIRC the tile-row-hints stuff does this sort of stuff just-in-time too, at compositing time, so effort isn't wasted on the various sorts of tiles, transient or otherwise, that never end up getting composited (but I'm an old man and my memory is getting hazy; I'd forgotten that the tile-row-hints stuff even existed and I should bloody well know). * For about a billion years I've been quite keen on the idea of lazily strong-hashing dirty tiles into a gimp-global hash table and collapsing multiple tiles with the same hash. There are so many hoops to jump through to make sure that the existing copy-on-write framework can actually be used in certain situations, mostly boiling down to having to use a central drawable-copy function that knows when it's possible to COW. Of course, plenty of GIMP's operations don't/can't use this function but still yield data that would in theory be COW-able. 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), that the normal COW routes miss. Since I suck, I don't have time to implement... stuff. But these are probably fun beginners' core-hacking projects. --Adam -- Adam D. Moss . ,,^^ adam@xxxxxxxx http://www.foxbox.org/ co:3 busting makes me feel good kthx bye
