It looks like any file may do but it might be tricky getting it to behave like that.
There is one constant though: whenever you open a file that was saved with a floating viewport, the last layout will be visible even if that wasn’t visible when exiting Rhino. I.e. when the layout is not shown over ¾ of the viewports in the main Rhino window, it is shown as one maximized viewport in the main Rhino window.
I see that it behaves as described (¾ layout, ¼ model viewport) at least when at the time of saving and closing Rhino the following are true:
- floating window is on a second screen and is not maximized
- main Rhino window is in 4-viewport state
- one of the 4 viewports in the main Rhino window is active
New file from factory default template “Large Objects - Millimeters.3dm”: test-test-open with layout.3dm (602.4 KB)