modelviewer should use toolbar buttons for view switching

The view selection buttons are a little better than the drop-down. But rather than have 9 buttons off to the right, how about adding a toolbar to the top of the window?

The "custom view" button in particular is very odd - because it doesn't do anything when you click on it. Same with the "Select View ..." that I added to the drop-down. The view selection buttons take you to that view - they don't lock the user into that view. To create a "custom view" all the user needs to do is click and drag. As I did with the drop down, as soon as the user drags, disable all of the view selection buttons.

So my suggestion is to add a toolbar to the top of the window with the following buttons: "Open", "Save QML" | "Spin", "Floor" | "Front", "Back", "Top", "Bottom", "Left", "Right", "Front/Right", "Back/Left", where "|" is a toolbar separator. You should be able to find open and save icons amongst the Qt application examples. And I'm sure "Spin" and "Floor" won't be hard to make up an icon. There's no need for "custom view" as it is implicit as soon as the user drags that all of the view buttons should be unchecked.

Eventually, we can add toolbar buttons for the Translation/Rotate/Dominant actions on the 3D mouse, although we probably don't need that on the first try.