Re: Display engine bugs

[Kim F. Storm]

Juri Linkov <address@hidden> writes:

> I found some bugs related to text displaying:

Thanks for your reports.

You forgot to tell which version and system you use though.

I'm looking into these problems, and have made some small progress...

> 
> 1. When a point is located on the second line from the bottom of the
> window, then scrolling down one line (e.g. by C-u 1 M-x scroll-down)
> moves point to the beginning of the current line.  This is a bug
> because the current line becomes the last line of the window and it
> remains visible, but its point moves to the line beginning.  

I can reproduce this.  No fix yet.

>                                                              I have
> also a related feature request: to preserve column position if a line
> becomes invisible after scrolling, i.e. to move point to the same
> column of the previous visible line instead of jumping to the line
> beginning as it does now.

This is a bit unclear -- how does scrolling make a line invisible?

> 
> 2. Scrolling the buffer screenfully with text in a proportional font
> sometimes moves a point into center of window instead of moving it
> into first or last window line.  Sometimes scrolling down towards the
> beginning of the buffer stops on the last line of the first screen
> and don't move further and don't signal an error.

Haven't looked at this yet.  A complete, self-contained test case would help!


> 
> 3. When window is split vertically (e.g. by C-x 2), the cursor
> (hollow box) don't appear immediately in the non-selected window.
> It appears here only after pressing some key or after some timeout.

This doesn't happen to me.  

What happens if you start
        emacs -q --eval '(blink-cursor-mode -1)'

> 
> 4. "Black hole"
> 
> Copy into scratch:
> 
> (progn
>   (setq tab-width 8 truncate-lines t)
>   (mapc (lambda (l) (insert-char (car l) (cadr l)))
>         '((?\n 1) (?\t 3) (?\040 5) (?a 75) (?\040 1) (?\n 1) (?\t 16))))
> 
> and press the following keys:
> 
> C-j C-p C-b C-b
> 
> now start to press <backspace> may times until you see a black hole.

I don't see this, but it does seem to be related to the next problem:

> 
> 
> 
> 5. Next bug can be reproduced by evaluating the following line:
> 
> (progn (setq tab-width 8 truncate-lines t) (split-window-horizontally))
> 
> Now set left window width to 82.
> 
> Insert the following line into buffer:
> 
>                          
> aaaaaaaaaaaaaaaaaa(xxxxxxxxxxxxxxxxxxxxxxxxxxx);(yyyyyyyyyyyyyyyyyyyyyyyy)
> 
> and press the following keys:
> 
> C-e C-SPC M-C-b M-C-b C-w
> 
> On the next screenshot the first line shows how it should look,
> the second line show how it actually looks.
> 

Yes, I see this.  I have some clues to what's wrong, but no fix yet.


-- 
Kim F. Storm  http://www.cua.dk