It’s actually the curve I’m selecting at the bottom left, sort of mirrored and projected onto the screen because I’m heavily zoomed in.
I can’t really reproduce this reliably, but it usually happens when:
You zoom in on a small part of a very long curve
You activate a tool that requires curve selection
You get the selection popup where you happen to click
I think the last part is very important, because at least this last time, I wasn’t able to reproduce it if I clicked somewhere that didn’t activate the popup (as I’m writing this, I’m able to reproduce the phantom curve any number of times until I change the camera angle).
Rhino has very few graphical glitches for me, but this is one of them. Anyone else experience this?
This may be a display bug in the selection drawing routine as (eobet) Robert guessed. I’ve encountered the same issue a few times, but it has mainly been innocuous.
When Rhino is asking which specific object you want to select and you highlight one of the choices, moving the camera so that the selection is both in the viewport and in its imaginary rear-view mirror view at the same time can cause the unwanted projection. You often won’t see the full (horizontally and vertically) mirrored object(s). The fillet in Robert’s video appears to shrink or actually move forward, because the camera is leaving it behind. Note, the pop-up selection choice must remain open.
To reproduce this, you can create a large sweeping curve/arc visible in the viewport that also curves around directly behind the viewport camera. Place another object overlapping this curve in the visible viewport. Select where those objects overlap so both appear as options in the pre-selection pop-up. Move the cursor to highlight the curve, leaving it highlighted. At this point, the sweeping curve may appear as a mirrored object. If it doesn’t appear, try tilting and/or panning the camera while it remains a highlighted choice. If it still didn’t appear, try moving the camera forward or backward toward the opposite ends of the arc. You want the geometry visible to the camera had it been turned around 180 degrees.
There is one more scenario where this occurs, that doesn’t involve the pre-selection pop-up. Highlight an entire model and turn on all of its control points. Now fly through the model. At some point, you will likely see new points appear and move away from you before they vanish. [Update: in this scenario, you don’t need anything selected, as long as the control points are visible]
I suspect both scenarios use the same routine.
When the pop-up selection is finalized, the mirrored object(s) disappear. If they were a pre-selection of points, they may continue to remain visible, depending on the location of the camera.
