Here's my take on it:
A user interface designer has to consider what the typical user thinks
should happen when rolling the mouse wheel forward or backwards.
For example, if the user thinks the mouse wheel moves her EYE closer to and
farther away from the image, then rolling the wheel forward zooms in.
If the user thinks that pushing forward on the mouse wheel moves the IMAGE
farther away from her eye (moving her finger, and thus the image, away from
her), then rolling the mouse wheel forward zooms out.
So it's all down to the user's mental model of the situation. Is she
manipulating the image, or moving her eye? A good user interface is one that
behaves in such a way that the behavior of the application does not conflict
with the user's mental model. So since it's difficult or impossible to find
out what your users' mental models are, and even if you could they wouldn't
all agree, there's just one good way to handle this.
And here it is:
Make the behavior a user-settable preference. For its default value, see if
you can find a consensus among the industry leaders in the same kind of
application you're developing. Look at Photoshop, Paint Shop Pro, etc. If
you can find a consensus, use that as the default setting. If you can't find
a consensus, ask as many as possible of real users of your application (not
just your programmer-testers) what they want to happen.
I'll go farther than that: some people might want the wheel to pan (and the
newest mice allow you to move the wheel left and right, as well as forward
and back). So you might consider letting the user specify in an options
dialog whether they want the wheel to zoom or pan. But if they want to pan,
there's the same mental model issue: are they moving the image left and
right, or the eye left and right? So they'd need to specify their preferred
directional behavior for both modes of operation.
All this is a lot of work, but at least in one small way your users will be
happier people when they're using your app.
Best regards,
Tom Dacon
Dacon Software Consulting
"Martijn Mulder" <i@m> wrote in message
news:44***********************@news.wanadoo.nl...
When the mouse is over a picture, the user can grow or shrink it by
rolling the central mouse wheel. What behavior is typical when the user
rolls the wheel away. Will the picture grow or shrink then?