Prusaslicer: Warn about overlapping objects when slicing

[PetteriAimonen]

Version

_PrusaSlicer version 2.2.0+linux+x64_

Operating system type + version

_Ubuntu 18.04_

3D printer brand / version + firmware version (if known)

_Original Prusa i3 MK3S_

Behavior

This is partly an user error, but I think it would be nice to have a warning about this as it is an easy mistake to make.

1. Open PrusaSlicer and switch to Preview [Ctrl+6] before adding any objects. (Alternatively: switch to preview after slicing an object and select Edit -> Delete all to remove it.)
2. Load a new object using menu: File -> Import -> Import STL. Note that the preview does not get updated, I guess this is a small bug also.
3. Go selecting settings. Because the preview didn't get updated, you forget that you already added the object.
4. Add the object again using File -> Import -> Import STL. Press Slice now and everything proceeds as normal.
5. Printer ends up extruding twice the amount of plastic as is desired, with terrible results.

I would want that when I press Slice now, PrusaSlicer would pop up a warning You have overlapping objects, are you sure you want to proceed?.

Like shown below, the problem is not visible in preview or 3d editor unless one drags the object with mouse.

[foreachthing]

And if I do that on purpose, then I get a warning about something I want? Could it be a exclamation mark in the statusbar? I really, really don't like popups!

[PetteriAimonen]

Yeah, I guess an exclamation mark near the slicing status output or even a line like "Overlapping objects: 2" could work.

[neophyl]

I opened this issue https://github.com/prusa3d/PrusaSlicer/issues/3678 about having an opacity/xray mode on the platter. With such a mode you would be able to tell from the opacity if there were multiples over each other as well as the primary purpose of placing modifiers inside objects more easily. 2 birds with one stone. Without a pop up :)

[rtyr]

Also related to this issue https://github.com/prusa3d/PrusaSlicer/issues/4520.