[brailleblaster] Re: StyledText default content model
- From: "John J. Boyer" <john.boyer@xxxxxxxxxxxxxxxxx>
- To: brailleblaster@xxxxxxxxxxxxx
- Date: Sat, 11 Jun 2011 21:37:50 -0500
Interesting, and good to know. I always like to know implementation
details.
John
On Sat, Jun 11, 2011 at 08:03:18PM -0600, Susan Jolly wrote:
> StyledText by default represents the entire text of a document as a single
> character array. So the only information it can know when it does a
> modification is the index into the character array of where the
> modification started and what characters were inserted or deleted. In the
> case of an insertion, the size of the character array is increased, the
> characters past the insertion point are shifted to the right, and the new
> characters are inserted directly into the correct place in the array. In
> the case of a delete, the size of the character array is decreased with the
> relevant characters removed and the ones past the deletion point shifted to
> the left.
>
> FYI, in practice, with an efficient implementation, there doesn't have to
> be a shift every time a character is inserted since the character array
> used for storage typically has a movable gap or empty section. (This
> approach was apparently invented by the emacs developers.) If a character
> is inserted or deleted, the gap is moved to the location after the
> insertion or deletion position since usually someone using an editor makes
> a number of consecutive insertions. However, the gap model is basically
> hidden and when StyledText sends event information, the character positions
> are the correct physical positions they would have if the storage array
> didn't have a gap.
>
> Susan
>
--
John J. Boyer; President, Chief Software Developer
Abilitiessoft, Inc.
http://www.abilitiessoft.com
Madison, Wisconsin USA
Developing software for people with disabilities
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