Modifier keys as pano "steering" controls
- As a general principle (and regardless of platform), I would argue
that modifier keys should not evoke ANY behavior when used alone.
This "rule" isn't just about the Macintosh Command key -- the Control
key on Linux or Windows rarely does anything when pressed by itself,
but only along with another key.
The most obvious modifier key (when typing) is the shift key.
Pressing a letter key while the shift key is held down modifies the
behavior of that key (usually, an "upper case" equivalent is
produced). Pressing the shift key alone probably shouldn't do anything.
I would consider the Shift, Control, Option (Mac) and Command (Mac)
keys all to be "modifier" keys. The Alt key is a little different...
rather than input being interpreted differently while it is held
down, *tapping* it switches to a *mode* where input is interpreted
differently. Typically allowing selection of menu items by typing
letter keys. For the Alt key, it is non-normal to continuously hold
it pressed down.
I might guess that the original QTVR "zoom" keys were chosen because
they allow a person to zoom the image with one hand (using keys near
edge of the keyboard) while changing the pan and tilt by dragging
with the mouse (placed on the opposite side of the keyboard) using
their other hand. I'll bet that if you did usability testing with
"ordinary" users they would, IN GENERAL, not use the mouse and the
keyboard at the same time. It wouldn't surprise me if, in fact, most
viewers of panoramas NEVER zoomed in or out!