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

[Alex Schroeder]

Eli Zaretskii <eliz@is.elta.co.il> writes:

> 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?

No.  Perhaps my description was unclear: While reading this message,
press M-x scroll-left.  While I write this, the entire text
disappears, and little arrows on the left fringe indicate that the
text has disappeared to the left.  Press M-x scroll-right to return to
the original position.  Now press M-: (scroll-left 78).  What do you
expect?  I expect the same behaviour as before.  But instead, "78" is
displayed in the echo area and the window remains unchanged.  Does
that explain what I am seeing?  Can you reproduce what I see?  I just
tried it again and I continue to think it is broken.

>> 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''.

I expect to be able to view the picture in the buffer using only keys
-- no use of the scroll bar should be required.  Thus, if scrolling
works on lines of text and the picture is considered one line of text,
the desired behaviour cannot be achieved.  I agree.  Consider it a
feature request, then.  :)

When the picture is equivalent to 200 lines of text and the window can
show 10 lines of text, then I expect to reach the bottom end of the
picture after hitting pg-down 9 times.

Alex.
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