Hi Mike - that's a display artifact / display imperfection which is just a normal side effect of how the display works.

The viewport display has an emphasis on generating an image really quickly, so there are all sorts of little display glitches similar to this which can happen - it's not really feasible for the display to work perfectly because generating the equivalent of a full offline render for every display refresh would make for a very sluggish display.

One of the types of display artifacts is having "bleed through" of edges and curves when they are on thin walls or just fairly close to the surface that should be obscuring them.

The display engine pulls edges and curves forward when they are displayed, so that the edge curves or curves that are drawn right on a surface are not partially obscured by that same surface that they are sitting on.

That forward bias pull can have a side effect of making some curves display as non-hidden when they are just a little distance below a surface. But without that biasing there would be a much worse display artifact of edge curves and curves drawn on surfaces being kind of "stippled" and having parts of themselves displayed as hidden when they are coincident with a surface.

In the future I want to make some tune ups to this area of the display to help reduce some of these display artifacts in some cases, but in general display artifacts like this are just a normal side effect of various shortcuts that are taken to meet the primary goal of having the display work really quickly, so they are really just things to ignore.

- Michael

And basically the resolution of the zbuffer that is used to track hidden surfaces by the video card has some effect on this all as well, and when you add more objects to the model the range of values that are used for the zbuffer will change, and so that's why you could see some differences in hidden surface display after you add an object.

Some of these kinds of things are just baked in to how 3D accelerated video cards are set up to work.

- Michael

Thanks for the thoughtful and clear answer. It is telling that when I see something strange in MOI I worry that it is an issue with my computer rather than the software. The model seems to behave perfectly with a tiny plane behind the model, and I am comforted to know that this is just an artifact.

Thanks again for your time.

You might want to make sure that individual objects are not using multiple styles. For instance, select an object and if it shows styles as "varies", then that could also attribute to the darker lines appearing more in the foreground of your display.

Michael T.