== Don't make your 'I am processing' animation too complex

This is a lesson from long ago, one that I learned from the very
first Amiga word processor. This word processor's mouse busy-cursor
animation was of a bird leisurely flapping its wings; because the
original Amiga was kind of slow, people wound up seeing this animation
fairly often. Several years after the Amiga was released, I wound up
talking to one of the people who had designed this (she was my [[HCI
http://en.wikipedia.org/wiki/Human%E2%80%93computer_interaction]]
teacher) and she asked me whether us actual Amiga users had liked the
busy cursor; the team who built the word processor had apparently been
proud of that particular feature.

I had to tell her that we'd pretty much universally hated it. The
problem was that it sure *looked* like the word processor was sitting
around wasting its time slowly animating a (complex) cursor instead of
spending that time actually doing whatever the slow operation was. That
things were slow was bad enough; to have the bird slowly flapping away
was salt on the wound, and intensely irritating.

This held true even for [[us Amiga programmers AmigaBusyCursor]], who
knew perfectly well that this cursor animation was actually a very
cheap operation that took basically no time. We may have known better
intellectually, but it didn't help the emotional impression; we still
wanted the program to stop being fancy and get on with it.

The whole thing left a powerful impression on me. I'm sure that you
can draw a lot of lessons from it, but the obvious one for me is
that you don't want to make your busy-cursor or other processing
animations too complex (or rather, you don't want them to look too
complex). Regardless of the actual work it takes, a complex animation
will leave the emotional impression that your program is spending a
bunch of effort on it instead of other, more important things.

The Mac's classic spinning-clock busy cursor may have been very simple
and basic, but it had the virtue of *looking* simple and cheap. I
suspect that a similar thing holds true for Firefox's throbber animation
(which is subtle in any case).

=== Sidebar: how the animated cursor was cheap on the Amiga

The Amiga display hardware had [[hardware sprites
http://en.wikipedia.org/wiki/Sprite_(computer_graphics)]], and one of
them was used for the mouse cursor. Changing what any sprite looked like
was a simple matter of updating the address where the display hardware
should fetch its bitmap data. The net result is that you could cycle
through a fixed, precomputed mouse cursor animation by just writing
a control register every so often.

(This also made moving the mouse cursor a very fast and cheap operation;
you just wrote a couple of control registers to change the X and Y
position of the cursor sprite.)