Re: The display margin

[David Kastrup <dak@gnu.org>]

storm@cua.dk (Kim F. Storm) writes:

> David Kastrup <dak@gnu.org> writes:
> 
> > The click information for GNU Emacs is quite insufficient, anyway.
> > XEmacs, as far as I can remember, can tell from an event what object
> > has been clicked on and what pixel relative to the object's origin
> > has been hit.
> 
> I have just added this information to mouse clicks and two functions to
> access it:
> 
> Function `posn-object' returns the object clicked on, either an image
> or a cons (string . pos), or nil if there is nothing special at the
> place where you click the mouse (use posn-point to look at that).
> 
> Function `posn-object-x-y' return a cons (dx . dy) which is the pixel
> coordinates relative to the top left corner of the object (image or
> character) that you click on.
> 
> In addition, the mouse cursor now changes to an arrow (rather than the
> text mouse cursor) when it hoovers above an image.

Rationale for that?  Just interested.  Maybe this should rather depend
on an appropriate image property?

> Finally, when you use a block cursor, images are no longer shown in
> "negative" when your window cursor is a filled block cursor (only
> the border of the image is highlighted now).  So clicking on an
> image no longer makes it "unreadable"...

Oh great.  That means that all the complicated image border creation
stuff within preview-latex becomes unnecessary, and we'll have to
check for this functionality conditionally.  Any good idea for a test
for whether the previous terror blinking or the new border blinking is
used on images?

> > I digress.  Anyway, I want more information from clicks.  At the
> > very least, the object they appeared on.
> 
> What more do you want ?

Well, further preview-latex usability problems are that Emacs often
goes ballistic when large height images are concerned, particularly
larger than window size images.  Scrolling those to a particular
viewing position is pretty much impossible, scrollbar interaction is
nonworkable, and scroll-wheel stuff is pretty much unpredictable as
well (there have been Emacs versions where wheel-use could lead to
lockup with large images, I am not sure whether this is currently the
case).

When using XEmacs on such images, repeated use of Pagedown scrolled
larger-than-window images through at a pace of about one normal line
height per keypress.  While this was far from scrolling a window worth
of material, at least the scrolling made some progress and one had a
possibility to see all parts of such an image.

In contrast, IIRC, Emacs does not even touch the window-vscroll value
(which would move by a fraction of the image) unless at the very end
of buffer.

One possibility to see the effect it to use

C-h i d m Emacs RET C-x 2

and drag the mode line of the upper window such that the "Emacs"
headline is only partially visible.

Repeated presses of C-v will then stop on the headline and not make
any more progress.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum