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Re: Multiple Undo devours RAM

On Jan 26, 2004, at 8:22 PM, Erez Anzel wrote:

[snip]


I figure that instead of storing the Undo and Redo stacks in memory, as
is currently done, perhaps theres a means of writing them out to disk.
There would be some overhead for each operation, obviously. Perhaps
this could be an option for the user. Or perhaps the hard drive is used
if real RAM starts getting tight, so as to avoid getting bogged down
with virtual memory.

[snip]

In my experience, you should just let the virtual memory system do its thing. It is most likely better at deciding when to transition from RAM storage to disk storage and back, it requires no special programming effort, and it follows the fastest possible I/O bath through the system. The better answer for you is to store your undo data more efficiently.

In a high end CAD like application that my company made, the solution was to treat changes of selection as undo events and only store "operations" with the knowledge that they implicitly apply on the (current) selection. Lots of information gets saved with selection changes, but they are infrequent compared to moves etc.

operation 0: select 500 objects containing 50,000 points
operation 1: move selection 150, -60
operation 2: move selection 0, 1
operation 3: move selection 0, 1
operation 4: select 700 objects
operation 5: set selection color red
operation 6: set selection color blue

As an added bonus, our users liked being able to undo selection changes. It was common for users to accidently select or deselect points due to clutter and sloppiness, but there was no harm done. Just undo :) We also let them save selections in a list with user specified names so they could get back to a favorite selection like "objects in layers 5,6,8 except master points" at any time.

One final trick is to treat objects deletions as just another kind of selection change. The deleted objects are retained in the undo record for the selection change even when removed for the document proper. When the undo record goes away either because of redo or because the user cleared the undo stack, everything gets cleaned up nicely.
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 >Multiple Undo devours RAM (From: Erez Anzel <email@hidden>)



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