Some preview-latex issues

[David Kastrup]

Hello,

there are a few issues with image support in connection with
preview-latex <URL:http://preview-latex.sourceforge.net> and XEmacs
coming up soon.  One issue is an old one: preview-latex replaces text
by an image for the purpose of display.  In Emacs, we simply do this
by having a "display" property pointing to the image.  In XEmacs, we
instead have to give the text an invisible text property and use an
end-glyph on the image (a begin-glyph incidentally gets made invisible
along with the text IIRC).  This different scheme makes for a crucial
difference between Emacs and XEmacs: in Emacs, the cursor can be _on_
an image.  With XEmacs, this is impossible.  The cursor will either be
on a character before the image, or on a character after the image.
An XEmacs image thus can never serve as a full substitute for a
character: it is not addressable in the buffer.

People seemingly don't mind much the cursor being not placeable after
the last character before the image.  At least I can't remember any
complaints so far.

Now as a request made with preview-latex in mind, we are getting some
new functionality into Emacs with regard to images: image slicing.
When using an image, one can specify a rectangular subarea to be
displayed instead of the whole image.  I hope to be able to use this
in connection with LaTeX macros and stuff to slice the image of an
alignment (such as a table) into individual table cells that will
then make up separately addressable items on the screen.  Since they
are packed tight without intervening characters in the buffer,
XEmacs' inability to place the cursor on any actual image (the text
itself is completely invisible) will become quite tiresome even in
case that such slices would be implemented in XEmacs.

In addition (I don't remember the issues completely, it has been some
time now) it may be that an end-glyph of an extent will be made
invisible if immediately followed by "invisible" text.

Another issue was that "balloon help" tended to block XEmacs
operation and got in your way: we had to make this customizable to
off with XEmacs (with Emacs there have been no complaint: the
"tooltips" of Emacs don't disturb normal editing processes, are not
decorated windows, anyway, and are in general "harmless").  For
some Windows versions of XEmacs, even complete crashes have been
reported if one did not disable the balloon help.

Is there maybe somebody interested of trying to work on some of those
preview-latex/XEmacs interoperability issues in the next time?

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum