I have to jump in here. Please, do NOT, under any circumstances make the mouse wheel work as zoom, directly. Using with CTRL or CMD is more than adequate. Having the mouse wheel immediately zoom is irritating beyond belief.
Google do this with their Maps and it's so bad I have to keep a second mouse (without wheel) on my desk just to use Google Maps due to the very simple fact that the above is made worse when trying to use a mouse like Apple's Magic Mouse. When a developer mixes up SCROLL, ZOOM and PAN in this way that Google have, it's virtually unusable with a Magic Mouse. The slightest movement of your finger on the mouse's upper surface and you've gone from studying the layout of some minor roads to a map of the entire planet. And when you zoom back in again, hey, you're somewhere else entirely. China maybe. Brilliant.
Let's look at this historically.
What's the name of the wheel thing on a mouse? It's a SCROLL wheel and it should be used for SCROLLING, not some other fancy control that might be specific for just one or a few apps. Every app in some way needs to scroll and that is what the wheel is for and not to...
ZOOM, whose origin is of course the camera and it really should operate as such. If on a camera you ZOOM in and then out again, you will be back to the same point. That's ZOOMING and shouldn't be confused with PAN. Certainly it should NEVER be combined with any PAN action. This is something so many get wrong. ZOOMING in and out should not change the centre of the image being manipulated. So the reverse action should get you back to where you started. Apps should do what they say they are going to do. Use a SCROLL wheel and it should scroll. ZOOM in or out should do that and just that. No PANNING involved at all. There's another way to do that.
It is a fault of many developers that they assume they know what the user wants to do, when in truth they only actually know what they might want to do in those circumstances and don't have a hope in hell of getting it right for more than a very few users. An app needs to be consistent and not try and change the obvious.
Apple got this right from the start and in their Human Interface Guidelines, published many years ago, they exhorted the developer thus:-
"Consistency should be valued above idiosyncratic cleverness"
It's as true today as it was then, but sadly most developers (even Apple) seem to have forgotten this. Trying to misuse the SCROLL wheel, or a ZOOM function for something else is nothing if not an attempt at idiosyncratic cleverness and it must be abhorred.
Sorry, a bit of a rant, but it angers me when developers ignore such basic guidelines and end up making the app a PIA to use. So please leave the SCROLL wheel to just SCROLL in SH3D. Zoom ONLY when combined with a modifier key and also please ZOOM in and out centred on the visible image, so reversing any ZOOM will take you back to exactly as you were before. PLEASE.
