bug#51596: image-transform-resize has inconsistent semantics wrt scaling up/down

[Juri Linkov <juri@linkov.net>]

> I made a quick review of other image viewers:
>
> emacs                  gthumb          geeqie                eog
> -----                  ------          ------                ---
> fit height and width   Automatic       Zoom 1:1              Best fit
> <missing>              Fit to window   Fit image to window   <missing>

What is “Fit to window”?  Does it distort the image
by changing its height/width ratio?

> fit to width           Fit to width    <missing>             <missing>
> fit to height          Fit to height   <missing>             <missing>
>
> How about renaming "fit height and width" to something that suggests
> that it behaves differently from "fit to width" and "fit to height", and
> then adding a new option "fit to window" that scales up or down as
> needed?

Its menu item already displays a hint “Best Fit”:

	["Fit Image to Window (Best Fit)" image-transform-fit-both
	 :help "Resize image to match the window height and width"]

> Perhaps we could even have a "smart" option that only scales images up
> larger than some height and width, and otherwise leaves them in their
> original size.  That's probably the one I would like to use, now that I
> think about it.  (I usually prefer to scale images up, but as you point
> out it's pretty useless to scale small icons to fit the window.)

Maybe a new user option (disabled by default) could scale up
like ImageMagick's '-resize' does.