Intersecting differences of triangular prisms flips faces #537
Description
System information
SolveSpace version: 3.0~64c0f62b
Operating system: Debian Buster
Expected behavior
I have essentially a rectangular prism that I wanted to cut two triangular grooves in, one "vertically" and one "horizontally" (same height, and intersecting - making vise jaws). So, one 2d sketch + extrude for positive solid, one 2d sketch and extrude as difference for one groove, then perpindicular 2d sketch and extrude as difference for other groove. It should look normal.
Actual behavior
Several of the faces are red, indicating they are back-faces. (The solver didn't fail - it thinks it succeeded.) It actually looks like I'm seeing thru missing faces, when I went and redrew it...
Forcing to trimesh does fix it (despite the lack of a solver fail message), but I would have guessed that this was a fairly easy geometry to handle - nothing curved :)
Additional information
open jaw-covers.slvs - the other is my reference linked in. (I'm not sure how to, or if I can, "re-seat" the origin of sketches to be able to simplify this one without redrawing)
OK, decided to not be lazy and re-draw a simpler test case.
and with workaround:
Update: exporting to STL or "show naked edges" without doing the workaround pops up this nice and half-scary message:
and the exported STL is missing the same faces that are missing in the app. As loaded into PrusaSlicer with (left) and without (right) the workaround:
