Re: Displaying scrollable images in a grid-layout

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

Eli Zaretskii <eliz@gnu.org> writes:

>> Try this:
>> 
>>      (defun show-data-dir-images (&optional ncolumns)
>> [...]

> After running this function, this works for me:
>
>    (set-window-vscroll nil N t)
>
> as long as (a) point is not on the first screen line shown in the
> window, and (b) N is no more than 24, which AFAICS is the pixel size
> of the small images created by the above function.

Yes but the whole point is to display only half of an image at the top.
This recipe is not ideal. In the real application I would have 2 images
(pages of a PDF) side by side, filling e.g 3/4 of the windows vertical
space.  Below these images are another 2 which are only 1/4-way visible.
Now I want to scroll these 4 images up by let's say the equivalent of
next-screen-context-lines in pixels.

Would this be a feature supported by Emacs ?

>> (setq-local scroll-step 1)
>> (set-window-vscroll nil 10) => Scrolls, but:
>> 
>> Redisplay performance (or something else) greatly suffers,[...]
>
> I don't see this performance hit.  [...]

I am not able to reproduce it either just now...

> The other points I made in my previous message and today still hold:
> there are limits to what Emacs will currently let you do with
> window-vscroll, mainly due to 2 factors:
>
>   . the basic desire embedded in redisplay to avoid showing partial
>     lines, unless they are unavoidable
>
>   . the automatic scrolling when point goes off the window
>
> Let me know if you need further help or have additional
> questions/issues about this.

Thank you.

-ap