[DRAMATIC MUSIC - Clunky percussion to summon the modeling demons but only from behind some kind of safe demon proof plexi-glass]
[Aidy] Different modeling approaches have different pros and cons. MoI3d or XNurbs uses a Nurbs approach.
So think infinite resolution like curves. MagicaVoxel uses a voxel approach, so very versatile
but can lack the modeling precision that you get with curves. Atomontage is another voxel example
and gives some examples of the pros and cons right there on the homepage. The amazing Media
Molecule 'Dreams' game takes a unique approach with distance fields (I think it is) and there are many
wild examples that people create in there. Those various modeling engines don't use a polygonal
approach like Blender. The thought process behind creating in those other applications if applied
to Blender might completely mess up our model. In Blender 2.9 there is a new extrude manifold tool
that has been included that almost gives us a kind of flexibility that we may not be used to
as polygonal modelers and that will come into the picture here shortly. The new extrude manifold tool
and in other cases the 3d print toolbox add-on are the main saviors for us in this polygonal based
world. To start us off in this video let's take a look at some polygonal based horrors and how
to avoid them. One of the curses of the polygon is that it isn't a real physical thing. It's more of
a lighting trick than a physical thing it isn't like say a flat piece of card in the real world.
That means though that we can do amazing things that the universe might not and that's great but
it also means we can fall into some unintuitive traps - dark mystical stuff in 3D that isn't really
allowed in the real world. One of the most simple and common ways the curse of the polygon manifests
itself is with two polygonal faces sat right on top of each other. If i select this face here we
can see we've just got one of one faces selected, and if i go 'Shift D' to duplicate it and then right
click just to cancel the translation part of it and drop it right back where the other one was.
We can see we've got two faces now. But as you can clearly see they're sat right on top of each
other. This is impossible to do in the real world say with a couple of pieces of card for example.
Card has thickness while a polygon doesn't it's infinitely thin, it's a true size zero. Blender
actually handles this example very gracefully though. Right now from a visual point of view it
actually looks fine. We wouldn't know of the horrors lurking beneath or rather within the surface. I'm
just going to make sure that this toggle x-ray isn't enabled though and we can do that with 'Alt Z'
with the shortcut and as you can see it still looks fine. But if we give one of these faces an
edge loop with 'Ctrl R' you can see things start to get a bit angry. Again just to emphasize the
x-ray mode if we go 'Alt Z' it's not as obvious there, so I'm just going to press 'Alt Z' again and
now we get into this angry sort of thing. And anger leads to fighting - 'Z-Fighting' to be precise.
Which is this bit of flickery trouble we're seeing on screen right now. Since the faces are in exactly
the same space blender doesn't know which one to show so this flickery shimmering paradox is
the result. This is pretty inconvenient not just because it probably is not the visual result we
want but because it makes any modeling we want to do way more confusing. Because which face, edge
or vertex are we really trying to operate on when there's two lots in exactly the same space. When we
have twin geometry like this how do we know we're not accidentally selecting the wrong evil twin.
Basically it's modeling nightmare material but it's super simple to fix (if it's just two faces
in the same space). So first of all i'm going to select this edge and dissolve it so 'X' and then
dissolve that edge, and then i like to check down here just to make sure the vertices option is also
enabled or maybe with 'F9' from time to time and now that edge is gone. To fix this double face
issue assuming this was more within a sea of faces and not quite as obvious as this because we could
just select and then delete the face of course and then it's problem solved, but imagine this in a sea
of faces we could just select all and then press 'M' to merge and then choose the 'by distance' option.
Now this nasty two-faced geometry is automatically cleaned up into one wholesome trustable face. Let's
imagine for a second that we're not being very careful and we've somehow invited this curse into
our 3d geometry's home. So we're back with two polygons right on top of each other and one has
an edge down the middle so we can see that glitchy Z-fighting. If we now try to fix the problem with
merge 'by distance' we'll still be left with these faces. Notice the vertex count - we're at six at the
moment if i just undo that we were at ten and then if i redo with 'Ctrl Shift Z' we see we're back
down to six, and we're sort of left with this kind of geometry if i just lift this up for a second
and peek beneath the murky depths. Now let's crank up the anxiety and dissolve that extra
edge, here's where things get a lot more sticky. There's two faces now but only four vertices.
Merge by distance will no longer work to rid us of that extra face and will ignore our cries for help.
At first maybe it seems okay, Blender does a pretty good job of rendering this after all.
But that isn't to say it isn't still going to give us problems. If we try to do any modeling with this,
using 'K' for the knife tool for example or 'Ctrl R' for an edge loop, we can see if we switch to vertex
selection - we got an extra vertex but no edge to connect and the knife tool failed completely.
So first of all i'm going to get rid of these two vertices that were created when the edge
loop tool didn't quite work. So 'X' to dissolve them. We're still left with two faces when clearly we
should just have one so first of all i'm going to come out of this kind of completely full screen
mode with 'Ctrl Alt & Space' and then just go 'Ctrl Space' so that we still maximize our view here
but we still got access to some of our menus here. So let's see how we might be able to remedy this.
In the mesh and clean up menu here i was a little surprised to see that there's nothing going to
help us in our particular case now or at least as far as i'm aware anyway and as well as in
the select menu, we can go 'select all by trait' there isn't anything that's going to help us
here either. To stress that in this example it's fairly obvious what we need to do we could just
select this face and delete it and then problem solved but what about if we didn't know exactly
where this sort of geometry was and needed to hunt it down. So i'm going to undo that just to bring
the problem back and really we need to break out some bigger guns particularly with our '3D Print
Toolbox' add-on that comes bundled with blender. But we need to make sure we open our preferences which
i'll do with 'F4' and then come over to our add-ons tab and if we just type in 'print' and just make
sure that's enabled there we'll then find it show up in our sidebar under the 3d print section here.
Just before we use this though i'm going to add a different context as this is a very overly
simplified example, so let's make it slightly more complicated at least. So from the top view here i'm
gonna (press) 'E' to extrude this and then extrude out the rest of the faces actually because i have the 'F2'
add-on enabled it means that i can come over and just select this one vertex and press 'F' and then
right click to leave it in position and we can easily create quads in these corners each time
we press F, and then i'm going to press 'Alt Z' just to make sure we're in x-ray mode, and then just
duplicate those with 'Shift D'. So we've kind of got our original problem over here - just a very simple
two faces set on top of each other, as you can see there we've got two selected, and then we have this
example on the left where it's not so isolated and it's running off into additional geometry.
If we run a 'check all' we'll see we have some bad contiguous edges and we also have some
non-manifold edges. We can click on these to find out where they are so our bad contiguous edges are
right here and the non-manifold edges are actually around the edge of this geometry as well, which is
nothing to worry about actually because even if we add a plane in here and just move it out
of the way for a second and then deselect that with 'Alt A' and then 'check all' for this object
you can see we've got non manifold edges there, if we click them clearly there the boundary edges, so
nothing to worry about there. So if we come back to this and check all again. The fact that we
have these non-manifold edges on the inside of our geometry is a little bit of a problem.
And bad contiguous edges as it terms these ones here are also something that we need to keep our
eye on. So we found problematic areas but to fix them is another matter. There's no way that i'm
aware of currently that will automatically convert our results and abilities to select them here like
this into easily deleting the faces causing the problem. It's the old-fashioned manual selection
process in these cases. Selecting these faces and just pressing 'X' to delete them is the way
to go. Then when we check for errors we get these non-manifold edges, well they're all around the
boundary of that so that's fine. If on the other hand you had a really bad case where thousands
of faces were like this, that's obviously going to take some time but maybe you have bigger problems
to worry about if you manage to get into that sort of trouble! But considering that we can run
a script like this to find these sorts of edges that are showing us that we have a problem with
our mesh, it stands to reason that it should be possible to also script something that can convert
that into a face selection to be deleted, so i remain optimistic for that sort of development for
the future. So for this example let's start with a simple plane and i've switched to a more neutral
colored matcap for this example and also we can currently see both sides, so i don't have
backface culling enabled anymore. That's just to make a point about extruding from this plane. So
let's make sure we have this face selected and just press 'E' to extrude out like this. Which i'm
betting is probably the direction that you would always extrude but a beginner i think could be
just as likely to extrude down the opposite way too and would probably see nothing wrong with
this. But if you have some experience with blender seeing me extrude down like that was the modeler
equivalent of rubbing the cat's fur the wrong way. Let's undo this and get a better look at this by
turning on the face orientation overlay now blue is going to show the front of the face
and red is going to show the reverse side of that. That's the side which would be culled if we were to
enable that. So to repeat that again if we extrude up you can see everything is fine, everything is
blue as it should be. If we extrude down instead we can see everything is red, this angry dangerous red.
If at this point we disable our face orientation and also enable our backface culling, we might be able
to see that basically the box has been flipped inside out. Not a huge deal really but like we
saw when modeling with two polygons sat in the same place, we'll get modeling problems here too.
Especially with booleans and so on. So we do need to be careful and know which way polygons are
facing. We'll also come across issues if you want to export the object into a game engine
where backface culling is usually the default for game materials. This is fairly simple to fix
though we just bring up our normals menu with 'Alt N' and we'll be able to make our polygons nice
and consistent with our 'recalculate outside'. But it would help if we had anything selected.
Sometimes of course if you're modeling the interior of a room for example though you might
want to choose 'recalculate inside'. Or we've also got the option to just flip what we've got selected.
Alright so not so scary hopefully, but let's increase our modeling anxiety a little by doing
a super common mistake and that's using the extrude tool and forgetting that this tool
is two tools in one - it's extrude AND move. So when we cancel with either the escape key or the right
mouse button we've only cancelled the second part of the operation - the move part NOT the extrude.
Visually everything looks fine and dandy but hidden horrors lay within. Now we basically have
our starting problem all over again where we've got two faces sat right on top of each other AND
we have a load of squished up geometry, so a bunch of geometry that had zero area. Using the 3d print
toolbox again it's pretty simple to track these problems down. But that's probably overkill all we
really need to correct these sorts of issues is a simple 'select all' and then 'M' to merge by distance.
And then if we just 'check all' again everything's fine. Perhaps something worse than extruding and
then not realizing that you've left that squished up geometry all sat on top of itself in place
is taking a box like this, so i've undone that again, so it's just a box with this edge loop that
runs down the center of it, and turning that into a shape like this. Before 2.9 we may have taken
one or two approaches so for example just added a horizontal edge loop and then maybe deleted the
vertices belonging to this edge and then select this edge and then press 'F' a couple of times.
Or probably simpler is to drop the height down a little bit and then simply just extrude up one of
the sides another option would be just to throw caution to the wind and just do some extruding
into existing geometry but this gets very messy very quickly and it's definitely not immediately
clear what requires to be done to clean that up. But now Blender has introduced a new tool
in 2.9 which allows us to essentially rub the fur the wrong way and not be mauled to death by
our geometry. So taking a look at this shape here we can just take this top face and extrude down
because if we look in the tool now we have an option to dissolve orthogonal edges and that looks
like it does a pretty good job to approximate that kind of shape. It's not all plain sailing though
because the modelling seas can get a bit choppy here because if we take a look at this side face,
part of it is squished up as you can see along there. So to correct this we could add an extra
vertex onto the vertical edge so let's select that edge there, right click - subdivide and then i've got
an extra vertex there. Then we can enable our auto merge and then i can [realizes we need the right snapping!]... And then i can make sure that
i'm on vertex snapping and then press 'G' hold Ctrl, snap it to that vertex and now that's all nicely
welded and we've not got any strange squished up faces anymore. So that's all problem solved or at
least it would be apart from we'd need to kind of do the same thing to the other side. So instead of
actually taking that approach i'm going to undo a few steps until we're just left with this again. So
instead of using the check box, if we just switch over to the extrude manifold tool which we can
find if we long press the 'extrude region' we get this little menu and we can switch over to extrude
manifold. Now we can see a little gizmo to show that we're in that tool now. Then if we try that
same extruding down like that and then switch to our selection and then just test that vertex again
we can see it's all nicely automatically welded for us - on both sides! So i think the safest bet is to
use the extrude manifold tool rather than for example pressing 'E' and then moving a little, and
then enabling the check box. One final note is that it's not always straightforward to extrude out.
Context is everything as usual, so extruding here is perfectly fine but if we're going to extrude
out here and obscure already created faces then keep in mind that that isn't a particularly clean
modeling style either. If we move this out the way we can see we have this face here. We can use our
3d print add-on to check for potential problematic areas and it has picked up that something's a bit
weird with this area. So let's undo that extrude, move back over to the extrude manifold tool
and try the same thing again. Switch back to select and we'll see what we've got, in fact let's go to
x-ray with 'Alt Z' and we're in face select mode and we can see that there is definitely no face right
here. In fact let's try a different view just hide these two with the 'H' key and we can see there's no
face there. That's all looking pretty good. I think the tool is still going to pick up a
little bit of a problem though so let's see what two faces it's referring to there, it's just this
down at the bottom and at the back. I think that just has to do with us needing to connect these
with the 'J' key and i'll do a 'Ctrl R' edge loop there and then connect these with 'J' and then at
the bottom with 'J' and then let's do another check and all of that has gone away. So it was a little
bit sensitive there and we didn't really need to clean that up but it satisfied the 3d print tool
add-on 'check all'. So this is going to be especially harsh and critical and in a lot of cases it's
going to be that useful first step in resolving modelling nightmares and then we can sleep easy.