Re: Image transformations

[Eli Zaretskii]

> From: Lars Ingebrigtsen <address@hidden>
> Cc: address@hidden,  address@hidden
> Date: Fri, 26 Jul 2019 10:58:47 +0200
> 
> Eli Zaretskii <address@hidden> writes:
> 
> >> (And anyway, if the user says :rotate 91, then we want to do
> >> ImageMagick, because we don't have a native transform for that yet.)
> >
> > We do?  I thought we wanted to _avoid_ ImageMagick at all costs, more
> > or less.
> 
> Not at all costs, surely?

I meant what I said: at all costs.

For example, let's assume some Lisp says ":rotate 90.001" -- would you
automatically invoke ImageMagick, or would you rather error out (so
the user or the program get their act together and fix the round-off)?

We implemented native support for the transforms that we decided are
necessary for handling images in most situations, the only exception
AFAIU being PhotoShop-like applications whose very purpose is to
manipulate images.  And for the latter we expect the caller to
explicitly request ImageMagick.  So I don't think we want to fall back
to ImageMagick by default.

> We want to try to insert an image that does what the user has
> specified, and that requires ImageMagick in some cases.

The users who want this will have to request ImageMagick explicitly.
It should be a very infrequent situation when they need to do that,
unless we have somehow made a serious mistake in our decision.

> (When Emacs has been built with that support, of course, which I
> think anybody who uses Emacs to view images on platforms without
> native image transforms will do.)

There are currently no platforms without native images, except those
who only support text-mode frames.  OTOH, I believe many downstream
distros build with ImageMagick by default, and will do so for many
years to come.  And we want to avoid as much as we can the instability
that this introduces into Emacs.