Re: Overlay mechanic improvements

[David Kastrup <dak@gnu.org>]

Richard Stallman <rms@gnu.org> writes:

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>
>     > Does this mean you turn off display of the image on the overlay when
>     > the text in that region is changed?
>
>     Very much so, yes.  Changing the text in the region would be a pain if
>     you could not see it, and changing it breaks the correspondence between
>     text and image anyway.
>
> I see.
>
> But you keep the overlay in existence -- how come?

Convenience.  preview-latex has a mechanism to run only a region through
LaTeX, so it is possible to regenerate only images in a region.  This
comes with its own shortfalls compared with regenerating the whole
document but is much faster and less disruptive as then only images in
that region flicker as they appear.

When editing a particular equation or other element, reusing its
original boundaries as the region to run through LaTeX is a natural
choice, so the retained overlay preserves those boundaries (and offsets
them visually) for the sake of the commands regenerating a region.

If you split an equation into two by editing it, "regenerating" the
image will replace the original overlay with two new ones: in fact, even
if the boundaries stay the same, the overlay will get replaced.  It
sticks around only until some new image is generated touching any of the
original region.

If you write, say, word_text instead of word\_text (throwing LaTeX into
inadvertant math mode), the resulting nuisance overlay will need to get
manually removed (with keyboard sequence or mouse click) after
correcting the syntax error since no image will reappear in that area
after the correction.  That tends to be a smaller net distraction than
having to hand-select your regions to regenerate in the common case.

-- 
David Kastrup