Right now the options are somewhat confusing and would benefit from some extra features/actions.
The most annoying thing is that the left click "move picture" option is flawed because it doesn't allow you to view larger than the screen pictures entirely.
Here's a few things I noted:
- "Mouse wheel + CTRL" isn't listed. (though it seems to be locked to zooming in/out - which is nice to have)
- Middle button action can be set to different actions in the "switching mode" tab ?! (this is confusing)
- The action labeled "move picture" does actually zoom to 100% if the zoom factor is bellow 100% before moving (when assigned to the left mouse button only).
- setting "move picture" to the right mouse button has a different behavior than setting it to the left mouse button (doesn't zoom to 100% first) .
Example:
One input method that I find effective is the one from fastpictureviewer:

Here are a few idea worth considering to improve the viewer mouse input behavior:
- Implement a new move method that allows to pan the entire picture with a single mouse move.(inverting the mouse/pan direction will probably be a welcome option too).
- implement something similar to the fpv magnification mode (ie primary zoom and secondary zoom settings allowing for example to assign Left Button = "Primary Zoom & Pan" | Left Button + CTRL = Secondary Zoom & Pan.
to ctrl click to 300% which returns to 100% as soon as I release the ctrl key and returns to default (presumably fit view) as soon as I release the left mouse button. - fix the zoom in out action to actually zoom AND CENTER at the mouse location.
- Label things more adequately and provide description on what the several options actually do.( cfr fpv screenshot above) If the action differ when assigned to different input they should not be labeled the same !
- Consider providing new input methods (click + drag for fine smooth zoom for example as opposed to the current step zoom only limitation)
- Consider changing the default mouse settings to a more appropriate image viewer behavior. (left click > selection box definitively feels strange for an image viewer)
http://newsgroup.xnview.com/viewtopic.php?f=60&t=29213