Re: Displaying scrollable images in a grid-layout

[Andreas Politz <politza@hochschule-trier.de>]

Eli Zaretskii <eliz@gnu.org> writes:

> I cannot try your recipe [...]

Try this:

     (defun show-data-dir-images (&optional ncolumns)
       (interactive (list 4))
       (let* ((files (directory-files
                      (expand-file-name "images" data-directory)
                      no-dot-files))
              (column 0))
         (with-current-buffer (get-buffer-create "*images*")
           (erase-buffer)
           (save-excursion
             (dolist (f files)
               (when (and (file-regular-p f)
                          (file-name-extension f)
                          (image-type-available-p
                           (intern (downcase (file-name-extension f)))))
                 (insert-image (create-image f))
                 (when (= (cl-incf column) ncolumns)
                   (insert ?\n)
                   (setq column 0)))))          
           (setq-local scroll-conservatively 0)
           (setq-local scroll-step 0)
           (setq-local scroll-up-aggressively nil)
           (display-buffer (current-buffer)))))

> That being said, I think you are missing the PIXELWISE-P argument of
> both window-vscroll and set-window-vscroll.  Aren't you?  

No both versions do nothing with above scroll settings for any argument
I've tried (unless the window is smaller than the first displayed
image).

> If not, please elaborate on what kind of partial scrolling did you
> want to see.
>

doc-view let's you scroll the page, i.e. the image is only partially
visible.  I want the same behaviour for more than one image in the
buffer. Possible display state with 2 images:

           ................
           .              .  Image 1
           .              .         
          +.--------------.+        
          |.              .|        
          |.              .| Window 
          |.              .|        
          |................|        
          |................|        
          |.              .|        
          |.              .|        
          +.--------------.+        
           .              .         
           .              .  Image 2
           .              .         
           ................         

But:

(set-window-vscroll nil 10) => Nothing happens.
(set-window-vscroll nil 99) => Nothing happens.
(set-window-vscroll nil 100 t) => Nothing.

(setq-local scroll-step 1)
(set-window-vscroll nil 10) => Scrolls, but:

Redisplay performance (or something else) greatly suffers, i.e. opening
e.g. the M-x prompt after I have executed the above 2 commands takes
about one second.  (I have tested this with emacs-git -Q .)

>> But it slows down redisplay considerably, to a point where it
>> becomes unusable.
>
> And there's one more thing that confuses me in this statement: partial
> pixel-wise scrolling will always be slow,

Not like that.

> so I'm not sure what exactly you expected to happen.  Probably again
> it goes back to the fact that I'm not sure what you were trying to
> accomplish, or why.

See above.  

Thanks for your answer.

-ap