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 #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 #4520 and #2501.

[edwardhorsford]

I was just bitten in a print by not noticing an overlapping part - a soft warning in the lower right would be great.

In my case I'd used + to duplicate a part many times. Unfortunately this part was small and ended up overlapping a larger part so I couldn't see it easily. Only when printing did I notice two parts had ended up merged.

If arrange let you arrange only items on the build plate I would use that and avoid this issue - but it arranges everything, including stuff off the build plate I don't want to currently print. The current solution of picking items manually isn't ideal if you can't see they're overlapping, nor if you have many items.

[DangeMask]

Today I had similar issue. I wanted to print a multipart model as one piece (no need to screw together for me), so I just overlapped the objects in slicer, roughly checked the preview and hit print. Then I realised the printer prints the overlapping parts twice. So I had to clancel the print, merge the objects in slicer and start again.
It just wasn't obvious to me that the slicer would behave this way. I believe a notification or exclamation mark would help with this. Maybe use the same way how slicer suggests automatic color changes for signs. It can also contain a quick link to "merge objects" which would help people who just want to merge objects and don't know about double printing of overlaps.

PS: I wanted to use "Add part" at first, which would solve this too. But i needed to cut some parts at first and the slicer only allows cut for the whole boject, not one part of it.

[ats1995]

For me an option to highlight the parts that overlap and warn would be super helpful when fitting parts densely on the build plate.