Line Numbers in Text Editor

Richard Gaskin ambassador at
Sat Jun 26 12:23:35 EDT 2010

Justin Sloan wrote:
 > I am planning to implement line numbers in a proprietary text editor
 > that I wrote for in-house use.  Problem is, I don't know how I am
 > going to implement it. I thought about using a parallel text field,
 > but there has to be an easier way.  Any of you genius devs have any
 > ideas?

I forked the MC IDE's script editor many years ago to add, among other 
things, line numbers.  It was at the time the only script editor for Rev 
which had line numbers, and having implemented this "advanced 
technology" <g> I can share with you a couple tips I learned:

The line numbers are displayed in a separate field to the left of the 
editor field, kept in synch with scrollbardrag handlers in each.  Being 
a script editor I also have another field in between them for marking 
breakpoints, but you probably won't need that for other types of editing.

I chose a separate field for the line numbers because it seemed a more 
with-the-grain approach than attempting to put anything in the editor 
field except for the script itself.  In Rev, a script is just a block of 
text, so my mandate for my editor was to maintain as close a 
relationship as possible between what you see and what the engine 
expects.  So the script is dumped into a field, with no caches or other 
intermediaries to complicate the scripter's relationship with the 
engine. WYGIWE - what you got is what exists. ;)  I have a McCabe algo 
for Rev (see note on RevCloud below) so I'm sensitive to the impact of 
complexity in a code base.

At first I went the route most other text editors use, in which the line 
number field is populated dynamically to show only the lines present in 
the editor field.  But I found that when I got beyond a few thousand 
lines the time it takes the engine to render the line number field 
became a performance drag on my typing.  So I went with having 
pre-populated numbers, which isn't so bad since you can still see how 
many lines you have in your script by just scrolling to the end and look 
at the last line number across from the last line of script.

But even pre-populating the line number field was not without some 
challenge, since putting in 10,000 lines of numbers would not be 
sufficient for some scripts, and added a lot of bulk to the editor stack 

So the final solution I went with was leaving the field blank when the 
stack is saved, and populating it on preOpenStack with the number of 
lines of the script + 5000.  Since this is a one-time performance hit 
when the stack opens, the impact on performance isn't nearly as 
noticeable as it was when I was appending that list with each carriage 
return (has anyone younger than 40 even seen an actual typewriter 
carriage? Odd nomenclature in the 21st century, but I digress).

This keeps the stack file small enough to be extremely portable (I'm 
migrating a lot of tools to cloud storage - look for RevCloud coming 
soon to RevNet this summer; think devolution on serious steroids and 
focused on collaborative workflows), and it's unlikely that a person 
will type more than 5000 lines during a given session with the editor open.

But what if they paste more than 5k lines?  I've trapped for that in the 
Paste item and add another block of lines numbers beyond the number 
already in the field + the number in the clipboard, so we stay a few 
thousand lines ahead of the scripter.


  Richard Gaskin
  Fourth World
  Rev training and consulting:
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