Funny that it is an accident, but so many tutorials on the web use boolean to do this. Almost all of them actually.
Bisect seems to work with a straight plane, but ultimately what I want to do is cut the 3D object with a “wavy” or “curved” plane. Ultimately the plane I want to cut with is actually a surface map that I can import to blender.
I now see people like the knife project, but the implementation looks different in 2.8. Do you happen to know of a good tutorial for knife project in 2.8 with a wavy plane? I will keep looking for one anyhow.
Select only the cube, enter edit mode, then in the outliner select the wavy mesh, and use the knife project operator.
In 2.79 you would select both before entering edit mode, since in 2.8 we have multi select edit mode, the cutter object has to be selected after enter edit mode, the outliner its the only way i found
I think you may find the current boolean to be reasonably reliable for your use case if you make sure the normal of the (wavy) plane you want to cut with is approximately aligned with the X-axis. (The “inside-outside” test that it uses projects rays along the X-axis direction.) So in your simple cube and plane case, rotate the plane 90 degrees around the Y axis. This isn’t ideal, of course, but if you really need to do this, you can rotate your whole model so that the cut you want works with an x-axis-normal plane cutter, and then rotate back afterwards.
The new boolean implementation I am working on should work pretty well for this case. It won’t assume that the two objects are both closed.
