[Lazarus] [!! SPAM] Re: Undo for Form Designer

Bogusław Brandys brandys at o2.pl
Mon Jan 4 13:07:13 CET 2010

Juha Manninen pisze:
> On torstai, 31. joulukuuta 2009 17:08:11 Mattias Gaertner wrote:
>> Notes:
>> Changing a property (e.g. Left) changes some other properties too and
>> there is no hook. So for undo you must store the whole form plus the
>> descendant forms plus the referenced forms plus the source changes. This
>> costs much time and memory. For example with some images you easily get
>> a megabyte.
>> So it would be unwise to create an undo step on every change.
> It should be possible to store only the changed properties, thus using less 
> memory. A simple comparison with the previous state reveals the changes.
> Descendant and referenced forms make it more complicated. I think they can't 
> be ignored because the program could end up being broken otherwise.
> Undo would be used mostly for Delete, Move and Size, as noted in other mails 
> in this thread. Including binary images in the undo buffer sounds like an 
> overkill. Such images are always loaded from an external image, they are not 
> edited or created in the Form Designer.
> My thought here were at "abstract" level because I don't know the code enough 
> now to create anything concrete.
> Regards,
> Juha Manninen
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Maybe it's overload but every state of project (every change to forms or 
config) could be stored in database like sqlite and reversed in one step.


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