> I've used rotated images to display a spinning 'busy' indicator in the modeline 
> in the past.  The corresponding package currently ships with a set of 
> pre-rotated images, but generating them in Emacs would be more convenient.

I used runtime svg generation for similar task, to display video notes (and its progression) inside Emacs.

It worked pretty nice, see the demo - http://lgarc.narod.ru/pics/IMG_3498.MOV

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lg