Re: Handling invisible text in bidirectional display

> From: Stefan Monnier <[email protected]>
> Date: Sat, 16 Jan 2010 14:56:10 -0500
> Cc: [email protected], [email protected]
> 
> > This is another design decision I needed to make -- how to handle
> > invisible text in the display engine modified to support bidirectional
> > text.
> 
> Great to hear you progress on bidi support!

I never stopped.  Progress is slow, but steady.

Things that work so far:

 . Display of bidirectional text, including line truncation and
   continuation
 . Scrolling
 . Cursor positioning according to point
 . Text insertion and deletion
 . Left-to-right and right-to-left paragraphs, including dynamically
   determined paragraph direction
 . Horizontal cursor motion
 . Text properties and overlays that affect faces

All this works only on a text terminal for now.  I know very little
about the GUI display back-ends we support, so others will have to
come on board and make the necessary changes there, when the time
comes.

> > Therefore, I decided to modify the code which skips invisible
> > characters, such that it will skip them in the visual order, until it
> > finds the first character that is outside the region covered by the
> > invisible property.  Note that the ``first'' visible character could
> > be before or after the invisible region, in the logical order.
> 
> It's consistent with the current behavior, so it's probably no worse
> than trying to preserve the current implementation.

Thanks for the feedback.