- [Host] In the previous movie,
we inserted a new edge loop
here at the bottom of this organically curved seat cushion.
We did that using the swift loop tool.
Now we're going to use that edge loop
as a sculptural element
for controlling the shape of the subdivision surface model.
I want to achieve a depression
or a notch here at the bottom,
which will then allow me to detach part of the model.
I want to end up with a soft seat cushion at the top
and a separate plastic base.
Constraints will help us control the transforms
as we move those sub-object selections around.
And the more complex the sub-object selection is,
the more helpful the transform constraints will be.
Currently we're seeing the subdivided version of this model.
Let's select it,
and in the, "modeling" ribbon,
we want to be in, "modify" mode.
So click on that if necessary.
Also, go down to the bottom of the stack
by clicking, "previous modifier" a couple of times
until we're at the level of the editable poly.
If we get in close on this border edge here,
we can see that these two faces are coplanar.
So these two faces are coplanar,
and actually every pair of faces are coplanar,
and that's because when we inserted the edge loop
we didn't actually change the shape of the model.
We just added detail.
Now we're ready to move that detail around.
Let's go into, "Edge," sub-object mode.
And if we previously selected that edge loop
then it will be selected.
If that's not the case for you,
you can double-click on an edge.
So if nothing's selected,
you can just double-click to select that edge loop.
So let's now try to transform this using our ordinary tools.
Grab the move tool,
and by default, we're going to be
in the view coordinate system,
and we'll be using the, "use pivot point center,"
but notice oddly, since we're in sub-object mode,
the gizmo is not located at the pivot point.
So we saw that in an earlier movie.
So let's try to transform this.
We can just move this up in the z-axis
here in the perspective view,
and that is moving up
but it's actually not doing a very good job
because if we get in really close
with the Control + Alt + Middle-Mouse,
we've moved that edge loop up a constant amount everywhere,
and what we really want is to maintain the relative distance
between these existing sub-objects
and the transformation that we're making.
In other words,
we don't want to sort of break the shape here.
We want to maintain the overall shape.
And the way to do that really
is with these sub-object constraints.
You could attempt to get a better result using
different reference coordinate systems,
or transform coordinate centers,
but for a complex sub-object transforms such as this,
the sub-object constraints
really will be the most effective.
They'll give you the most control
because constraints allow the transforms to operate
in the space of the surface itself,
rather than in the space of some
chosen transform or coordinate center.
That means, for example, we can move sub-objects
around on the model
and not disturb the existing shape or form.
Constraints are found in the, "edit" panel
of the modeling ribbon.
They're also found in the, "edit geometry" rollout
of the, "modify panel," we'll see constraints here too.
By default constraints are disabled,
and that's indicated here in the, "edit" panel
by this button on the left, "constrain to none,"
that's currently highlighted, meaning constraints are off.
Okay, so let's try it.
We'll undo the transformation we just made.
Click on the, "undo" button,
and let's try, "constrain to edge" first.
Enable that.
Constrain to edge works best with vertex selections.
Let's convert this edge sub-object selection to vertices.
Hold down the control key,
and click on the, "vertex sub-object mode" button
that converts that edge election to vertices.
And with constrain to edge active,
we can click and drag on the move gizmo
and position those points around.
Make this easier to see,
let's maximize this view with Alt + W,
and we can even isolate the object with Control + Alt + Q.
Orbit around with Alt and middle mouse.
We don't actually need to use the transform gizmo
as long as we've activated the z-axis here,
we can click directly on these vertices
and move them around constraining to their edges.
So we're shifting that detail around,
but in this case we're not actually changing
the shape of the model.
All right, so that's constrain to edge.
Let me move this up a little bit.
You can see, we want that to be somewhere up there.
Let's talk about constraint to face.
That doesn't really apply that much in this case
but let's just demonstrate it.
I'll switch over to constraint to face.
And I'll just select one vertex over here
on the front of the model
and oar it around with Alt and Middle-Mouse.
So we can see that kind of edge on, or at an oblique angle.
And if we move in the Z or the x-axis,
we'll see that we're not actually
changing the shape of that surrounding area.
We're constraining to the flat surface of those polygons.
So that at is how constrain to face works.
I want to do that a few times and take that back where it was.
Finally, we can push sub-objects inward
or pull them outward by constraining to the local normal.
A normal is an imaginary line
that sticks out from every surface.
In this case, we're talking about face-normals,
also known as surface-normals.
A face-normal sticks out from each polygon
at 90 degrees to the polygons plane.
To push all these vertices in, relative to the face normals,
switch over to constrain to normal.
And once again, we just click and drag on a selection.
So let's go back to our selection that we had a moment ago.
Control + Z,
and we don't even need to use the transform gizmo.
We can just click and drag on any one of these
and we can push them in, or we can pull them out.
We can only move in the space of the local normal.
So the transform gizmo is not applicable in this situation.
So that's pretty cool,
but we may have introduced some error
along the seam of our symmetry model.
So let's go back to our four-view port layout with Alt + W.
Take a look at this
and we'll get in close in the front-view port.
And we've introduced just a little bit of error.
Those vertices are no longer
precisely at an x-position of the world.
We'll take a look at cleaning up that problem
in the following movie.
For now, we can just go back to object mode,
and we can go back up to the top of our modifier stack.
Maybe select that in the, "modify" panel,
and go back to unisolating, once again, Control + Alt + Q,
and we've just created that little depression
that was trying to achieve.
That's how to use constraints
to move complex selections of sub-objects.