Optimise clone memory use

[Daniel Pope]

Clones are using a very large amount of memory.

I'm trying to construct a lawn using individual blades of grass. To do
this, I clone a blade of grass, group a bunch of clones, clone the group
and so on.

This approach requires O(log n) SVG elements to create n clones.

However, this is not observed behaviour. Inkscape memory usage appears
approximately to grow with visible blades of grass.

I expect this behaviour from duplicates which is why I'm using clones. For
clones I expect the CPU usage to be slightly higher as the clone tree is
walked on demand, but memory usage should remain low.

[Daniel Pope (djpope)]

Originator: YES

Incidentally, grouping or ungrouping clones of groups of clones of groups
of clones takes ages.

If clones were implemented as a shallow reference rather than a deep copy
this should be instant too, shouldn't it?

[Buliabyak-users (buliabyak-users)]

Originator: NO

That's because most memory is taken by the renderer, not by SVG tree. This
should be much better when we switch to cairo. For now just draw it all in
outline mode (it is already cairo) and you will see memory won't grow
nearly as fast.