Re: Image transformations

[Eli Zaretskii]

> Date: Sat, 29 Jun 2019 20:49:59 +0100
> From: Alan Third <address@hidden>
> Cc: address@hidden
> 
> > This function is about the capabilities of a frame.  AFAIK, in an
> > Emacs built with ImageMagick support we will use ImageMagick for
> > everything, unless the user somehow forces us not to, isn't that so?
> > If so, the function is correct disregarding the image library in use,
> > since if the caller wants a specific image library, that caller will
> > have to figure out on their own what transformations are available.
> 
> If I were to do:
> 
>   (insert-image (create-image "image.png"))
> 
> Emacs will use libpng, whether or not ImageMagick is available. I
> would have to force ImageMagick use. You may be thinking of
> image-mode, which inserts ‘:type imagemagick’ if you rotate or scale
> an image using the key bindings (+, -, r).

So you are saying that a Lisp program needs to explicitly request
ImageMagick if it wants to, say, rotate the image by 45 degrees?  If
so, I guess either the ImageMagick capabilities should not be part of
the list we return, or the function should accept an additional
argument which is the image type.  The latter sounds like entering the
area of diminishing returns, since if the caller needs to specify
imagemagick as the type, then the caller already knows what will be
returned as the value, right?

So on balance, I think we should return a list of either 2 values or
(on Windows 9X) 1 value, and that's it.  WDYT?