You can make hairs
in a hair system collide with themselves and with other objects.
As an alternative or in addition to setting objects to collide with
hair, you can use hair constraints that act as implicit collision
objects. These can be helpful if hairs are getting stuck in surfaces,
since these implicit collision objects are volumes, not shells.
Also, you can set the collision object constraints to affect specific
hair curves, whereas Make Collide and the other
collision options affect the entire hair system. The combination
of collision constraints and geometry collisions can provide robust
collision, while at the same time preserving fidelity of the collide
object surface. For more information about the Collide
Sphere and Collide Cube implicit
collision objects, see
Set up hair constraints.
NoteIterations (Dynamics)
increases the number of collision tests. A setting of 8 does twice
as many as 4. This can improve the results of collisions in some cases,
but will also slow down the simulation calculation. If you increase Iterations you
need to lower Stiffness to compensate.
Fine tune collisions
If hairs are getting
stuck in colliding surfaces, consider the following:
- Avoid sharp or open edges. Rounded, closed
objects collide better with hair. The collisions are with discreet
points (like particles), not lines, so thin edges can slice between
vertices. The more CVs there are on the hair the more likely it
is to collide with a small edge. The number of hair CVs is determined
by the number of CVs on the Start curve times the Sample Density on
the follicle node. Collide Oversample values of
1 and 2 will insert extra midpoint CVs at collide time.
- If the effective collision width is zero
then hairs are less likely to fall through surfaces. The effective
collision width is:
Clump
Width * Clump Width Scale + Hair
Width + Collide Width Offset
By making the Collide
Width Offset a large negative number, such as -1000,
you can force the collision width to always be zero. This will cause hair
clumps to penetrate half way into surfaces. However they will be
less likely to fall through a surface.
- Increasing the Collide Oversample value
can help. Collide Oversample values greater
than 2 behave in a different manner. Values of one or two insert
new test points between the simulation CVs. This is good when there
are not enough CVs on the curve to catch collisions with thin edges. For
values greater than this the extra sample points are in a ring about
the CV center. This is better for handling wide hair clumps and
avoiding sticking. So to avoid zero width hair clumps being sliced
by thin edges, use values of 1 or 2; making the Collide
Width Offset negative in this case further helps. To
better handle wide clumps try Collide Oversamples of
3 or greater.
To make hair collide with the ground
- In the hair system’s Attribute
Editor, turn on Collide Ground in
the Collisions section. The “Ground”
is the ground plane (or the grid).
- Optionally, adjust the Ground
Height value, which is relative to the ground plane.
To make hair collide with objects
- Select the hair system. (
Window > Outliner)
- Shift-click to select the object or surface
you want the hair to collide with.
- Select
Hair > Make Collide.
A geoConnector node
is added to your collision object.
If your collisions are
not working, make sure Collide is
turned on in the hair system Attribute Editor.
For more information, see
Collisions.
If your hair is penetrating
the collision object, then you can try the following:
- Increase the Tessellation value
in the collision object’s geoConnector node.
- Increase the Collide Over Sample value
in the Collisions section of the hairSystemShape.
To make hairs collide with themselves
- In the hair system’s Attribute
Editor, turn on Self Collide in
the Collisions section.
- Adjust collision settings, including
the Collide Width Offset.
