Mouse wheel default behavior

[magnunor]

As far as I know, zooming and panning of (at least) 2D signals is only possible when using the Pan/Zoom tool. However, it would be nice if the mouse wheel zooming was enabled by default when opening images, as this is the standard behaviour for many image viewers.

So if you load some image into HyperSpyUI, it should be possible to zoom and pan using the mouse without having to find the Pan/Zoom tool, as this (in my opinion) is how most(?) people expect image viewers to work.