I think the diagonal shows because you have show edges turned on.

multtmatrix definitely works with difference. If you fill in the matrix to
be the same as a rotation then it does exactly the same as a rotate().
Internally OpenSCAD just does the same thing. Try adding a # in front of
one to see where the hole ends up.

What don't you understand about clockwise-ness? Looking from the outside of
the polyhedron at the face its points need to be in clockwise order in the
faces list. Otherwise OpenSCAD will think the face is facing the other way
and it will show up as purple in the ThrownTogether view, which indicates
an inside face, not an outside one.

On Wed, 20 Jul 2022 at 11:57, Bogdan Caramalac via Discuss <
discuss@lists.openscad.org> wrote:

On Wed, Jul 20, 2022 at 12:09:39PM +0100, nop head wrote:

To be clear: whatever way you list it, the side from which you can
look at it such that the points are clockwise, THAT's the side
that's outside.

So suppose that I have P0, P1, P2 = 0,0,0 , 1,0,0, and 0,1,0.

so if I list them P0, P1, P2, then they are anticlockwise if you look
at them from positive Z. But if you look from negative Z that's
clockwise. So negative Z is OUTSIDE the object, and positive Z is inside.

To help you figure this kinds of errors out, there is
"throwntogether", and openscad will color purple the sides of planes
that are defined to be on the inside of objects. Normally you
shouldn't be able to see any of those.

Roger. 

--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
**    Delftechpark 11 2628 XJ  Delft, The Netherlands.  KVK: 27239233    **
f equals m times a. When your f is steady, and your m is going down
your a is going up.  -- Chris Hadfield about flying up the space shuttle.

Rogier Wolff wrote:

Thanks for the tip! It seems the bottom was inside out and that caused the renderer to fail!