- [Instructor] Before we begin modeling with SubDs.
I'd like to cover some best practices
to hopefully help you avoid typology issues
that can often occur with subdivision, surface modeling.
SubDs work best on quadrilaterals.
That is polygons with exactly four sides or four edges.
All these cubes or boxes are built of all quadrilaterals.
The sphere and the cylinder primitives
also have triangles built into them.
Those triangles meet at a single point
which is known as a pole.
That's not currently visible on the cap,
so the cylinder but we'll get to that in a moment.
A pole is a structure where five or more edges meet
at a single point.
SubDs don't handle poles very well.
They're really optimized for situations
in which four edges meet
at a single point or a grid structure.
And a pole will adversely affect the subdivision surface,
even if the edges are inside a polygon
and therefore hidden by default.
Let's talk about polygons and triangles.
I've got my statistics listed up here in the upper left.
Remember that the keyboard shortcut for that is seven.
And remember that we can choose the options
for statistics from the viewport's configuration window
in the statistics tab.
And I'm displaying the total and the selected statistics.
I've also chosen to enable the triangle count.
So if I select an object such as this cube over here
I will see the number of polygons
and the number of triangles.
The triangle count is the true level of detail.
And that's important for interactive performance
rendered times and SubD modeling.
Remember that polygons are composed of triangles
even if we can't see them.
Triangle edges interior to polygons are important
but they're hidden by default.
To enable their display, let's select all the objects,
go to the display panel,
and in the display properties rollout,
disable edges only.
And can now see the internal structure of each polygon.
Take a look at the cylinder caps.
The top and bottom of the cylinder
are many sided polygons composed of many triangles
that all meet at the center or pole, just like the sphere.
Let's add an open SubDiv modifier to all these objects
and see the results.
With all those objects selected,
go to the modified panel, from the modifier list.
We'll add an open SubDiv.
We can just type in OP and click open SubDiv.
We can see that the cubes appear
to have maintained their structure pretty well,
except for the one on the left
which has become really rounded out.
And that's because the cube
on the far left had extremely low level of detail
to begin with.
The other two cubes had some definition
around their corners.
If we select any one of those objects
and adjust its open SubDiv modifier,
we will affect all of them
because we've instanced the modifier
onto all of the objects.
We did that simply by selecting them
before adding the modifier.
And we know this OpenSubdiv is instanced
because it's displayed in italics.
Let's bring the number of iterations down
to zero so we can check the polygon counts
for the original base object or control cage.
This cube over here is composed of six polygons.
Each polygon is divided into two triangles,
so we get 12 triangles.
Okay. Now let's increase the number of iterations
and see what happens.
Set the number of iterations to one
and check our polygon count statistics,
we've quadrupled the level of detail.
We now have 24 polygons and 48 triangles.
For an object that's built of all quadrilaterals,
increasing the iteration's value by one
will multiply the number of polygons
and triangles by a factor of four.
At two iterations,
we're multiplying the base object level of detail
by four times four or 16.
The cube on the far left has almost turned into a sphere.
We've got now 96 polygons and 192 triangles on that object.
Okay, I'll go back to the display panel.
We'll select everything and disable edges only.
And back over in the modify panel,
we can choose to visualize all of the polygon edges
by disabling isoline display.
And that helps to illustrate the issues
with poles on these objects here.
The sphere and the cylinder have now
got this problematic structure.
That's not going to deform very well
and you could actually have issues with rendering.
So I can't really do much for this sphere
but I can actually fix this cylinder pretty easily.
All I need to do is chop that cap up
so that it's all quadrilaterals everywhere.
I'll select that cylinder
and temporarily remove the OpenSubdiv,
just select that modifier and click the trash can.
I want to cut all quadrilaterals
on the top of the cylinder and that'll work best
if the number of sides is a multiple of four.
I'll set the number of sides to 16
and we want to use the cut tool.
So let's convert this to editable poly.
Right click convert to editable poly.
Let's zoom in on that with the z key
and we want to access the cut tool.
So scroll down in the modified panel
in the edit geometry rollout, we've got cut.
We can activate that
and tumble around with alt and middle mouse.
I want to cut three new edges horizontally
and three new edges vertically.
So I'll just click on one vertex
go over to the next vertex and click
and that's a single new edge.
Right click to exit that single cut operation
and repeat that process a few times.
Right click in between each one of these cuts.
So that's three running horizontally.
We also want three running vertically.
I'll just take one second to finish that up.
And once we've done that
we can right click again to exit the cut tool.
Now we have quadrilaterals everywhere.
Each one of these polygons has four sides.
Even these over here, which are roughly triangular
they're actually composed of four edges or four sides.
And now we've got a much better structure,
we can readd our OpenSubdiv modifier
simply by cutting and pasting
from one of the other objects.
Select one of the other objects,
right click on its OpenSubdiv modifier,
choose copy, go over to the cylinder,
right clicking its modifier stack
and choose paste instanced.
And now you can see we have a much better structure there.
It's built of all quadrilaterals,
and if we compare that to the bottom,
by orbiting with alt and middle mouse,
we can see the difference.
This is what we get from a polar structure
and this is what we get from an all quadrilateral structure.
And that's going to deform much better,
we probably won't have any errors rendering.
I recommend that you follow this practice
for all of your SubDiv model projects,
try to build your object out of all quadrilaterals
and try to avoid poles where five
or more edges meet at a single point.