Re: Image transformations

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 28 Jun 2019 22:50:52 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: emacs-devel@gnu.org
> 
> > Date: Fri, 28 Jun 2019 19:36:04 +0100
> > From: Alan Third <alan@idiocy.org>
> > Cc: emacs-devel@gnu.org
> > 
> > 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.

All done and pushed to the master branch.

Thanks for the feedback.