Re: scroll-up, scroll-down, scroll-left, scroll-right

[Eli Zaretskii]

On Tue, 23 Oct 2001, Alex Schroeder wrote:

> scroll-left and scroll-right don't work like they did in Emacs 20:
> Giving them an argument doesn't do the right thing.
> 
> When I use M-x scroll-left, the window is scrolled left.  When I use
> M-: (scroll-left 20), Emacs will show "20" in the echo area, but the
> window is not scrolled.

Try "M-: (scroll-left 60) RET", and I think you will see that it _is_ 
scrolled.

> According to the doc string, "Scroll selected
> window display ARG columns left."

Yes, but then it goes on to say this:

  "Default for ARG is window width minus 2."

So when you say "M-x scroll-right", the window is scrolled 78 columns to 
the right (assuming an 80-column display).  If the lines in the 
window-ful of text you were looking at are much shorter than 80 columns, 
you need to scroll left quite a few columns to see anything.  In 
particular, if no line is longer than 60 columns, (scroll-left 20) will 
not show any text.

Does that explanation help?

> The same is true for scroll-right in a window showing text.  When I
> use M-x scroll-left the window is scrolled.  When I then use M-:
> (scroll-right 20) in order to scroll back, Emacs prints "58" in the
> echo area, but the window is not scrolled.

Same here: try "M-: (scroll-right 60) RET".

> The behaviour of scroll-up and scroll-down with an argument is
> different and also broken in windows showing a picture.  If when I
> open a big picture, the top left corner is displayed.  When I use M-:
> (scroll-up 10), the bottom right corner is displayed.  Instead, Emacs
> should display the area of the picture below the top left corner --
> something along the left edge.

Really?  And what should it do if you say (scroll-up 1000) or
(scroll-up 5)?

In other words, since the argument to scroll-up is in units of text 
lines, what interpretation would you suggest for it in a buffer that 
visits an image?  Currently, it just goes to the end, since an image is 
treated as a single ``line''.