bug#10739: Animated TIFFs

[Glenn Morris <rgm@gnu.org>]

Package: emacs
Severity: wishlist
Version: 24.0.93

I can't say that I have ever heard of animated TIFFs, but it seems to be
trivial to add support for them: just add `tiff' to image-animated-types.
Actually, the one example I looked at had no specified delay, so it
would actually be necessary to modify image-animated-p to provide a
default delay.

I imagine these are mostly used for multi-page documents rather than
animation, so there should probably be separate new commands to step to
the next and previous sub-image in multi-image file.

So, perhaps the right thing to do would be to add an image-multi-p test
function. If that returns non-nil, you are given the option to step
through the multiple sub-images. Additionally, if a delay is specified,
you are also offered the option of animation.

Also, since ImageMagick allegedly supports the :index attribute in more
file formats, those could all be animated too.