Set the backgroundcolor of all lines a field to null

[Richard Gaskin]

There's a lot in that, Brahmanathaswami.
http://lists.runrev.com/pipermail/use-livecode/2018-August/249651.html

2000 lines is not much.  I suspect any time spent is relating to needing 
the redraw the field each time it's touched.  Try locking the screen at 
the top of the handler and see if that helps.

Also, my question about the algo itself was unaddressed.  If you can 
describe what you want it to do I'm sure we can find an efficient solution.

-- 
  Richard Gaskin
  Fourth World Systems
  Software Design and Development for the Desktop, Mobile, and the Web
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