Re: Image transformations

[Eli Zaretskii]

> Date: Fri, 28 Jun 2019 19:36:04 +0100
> From: Alan Third <address@hidden>
> Cc: address@hidden
> 
> I tested before and after I moved the HAVE_NS checks and removed the
> inversion from nsimage.m and it all works, so I’d say you’ve done a
> good job. We may as well use the same calculations for W32 and NS.

Great, thanks for testing.

> > There's a FIXME in image_set_rotation, please tell what you think
> > about it.
> 
> I think you’re probably right that we should throw an error there.

OK, will add that.

> > Please also comment on image-transforms-p.  Maybe we should return
> > both 'rotate' and 'rotate90' in the list when ImageMagick is
> > available?
> 
> Yes, we probably should.

Will add.

> My only concern is that there is no simple way to tell whether you
> should be using ‘:type imagemagick’ or not.  There’s no automatic
> fallback between types. I know we want fallback in principal, but
> I’d imagined it done at the lisp level, and this function doesn’t
> help too much.

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.

> > +image_set_rotation (struct image *img, double *rotation)
> 
> Should we rename this to compute_image_rotation to mirror
> compute_image_size?
> 
> > +image_set_transform (struct frame *f, struct image *img, matrix3x3 matrix)
> 
> I don’t think we need to pass this a matrix any more?

Makes sense on both counts, will do.

Thanks.