174 lines
6.0 KiB
ReStructuredText
174 lines
6.0 KiB
ReStructuredText
|
||
********
|
||
Interior
|
||
********
|
||
|
||
In between each neighboring vertex of a mesh, you typically create edges to connect them.
|
||
Imagine each edge as a spring. Any mechanical spring is able to stretch under tension,
|
||
and to squeeze under pressure. All springs have an ideal length,
|
||
and a stiffness that limits how far you can stretch or squeeze the spring.
|
||
|
||
In Blender's case, the ideal length is the original edge length which you designed as a part of your mesh,
|
||
even before you enable the Soft Body system. Until you add the Soft Body physics,
|
||
all springs are assumed to be perfectly stiff: no stretch and no squeeze.
|
||
|
||
You can adjust the stiffness of all those edge springs, allowing your mesh to sag, to bend,
|
||
to flutter in the breeze, or to puddle up on the ground.
|
||
|
||
----
|
||
|
||
To create a connection between the vertices of a soft body object there have to be forces
|
||
that hold the vertices together. These forces are effective along the edges in a mesh,
|
||
the connections between the vertices. The forces act like a spring.
|
||
Fig. :ref:`fig-softbody-force-interior-connection` illustrates how a 3×3 grid of vertices
|
||
(a mesh plane in Blender) are connected in a soft body simulation.
|
||
|
||
.. list-table::
|
||
|
||
* - .. _fig-softbody-force-interior-connection:
|
||
|
||
.. figure:: /images/physics_soft-body_forces_interior_theory-1.svg
|
||
:width: 180px
|
||
:figwidth: 180px
|
||
|
||
Vertices and forces along their connection edges.
|
||
|
||
- .. _fig-softbody-force-interior-stiff:
|
||
|
||
.. figure:: /images/physics_soft-body_forces_interior_theory-2.svg
|
||
:width: 180px
|
||
:figwidth: 180px
|
||
|
||
Additional forces with Stiff Quads enabled.
|
||
|
||
But two vertices could freely rotate if you do not create additional edges between them.
|
||
The logical method to keep a body from collapsing would be to create additional edges between the vertices.
|
||
This works pretty well, but would change your mesh topology drastically.
|
||
|
||
Luckily, Blender allows to define additional *virtual* connections.
|
||
On one hand you can define virtual connections between the diagonal edges of a quad face
|
||
(*Stiff Quads* Fig. :ref:`fig-softbody-force-interior-stiff`),
|
||
on the other hand you can define virtual connections between a vertex and any vertices connected
|
||
to its neighbors' *Bending Stiffness*. In other words, the amount of bend that is allowed between
|
||
a vertex and any other vertex that is separated by two edge connections.
|
||
|
||
|
||
Settings
|
||
========
|
||
|
||
The characteristics of edges are set with the *Springs* and *Stiff Quads* properties in the *Soft Body Edges* panel.
|
||
See the :doc:`Soft Body Edges settings </physics/soft_body/settings/edges>` for details.
|
||
|
||
|
||
Tips: Preventing Collapse
|
||
=========================
|
||
|
||
Stiff Quads
|
||
-----------
|
||
|
||
To show the effect of the different edge settings we will use two cubes
|
||
(blue: only quads, red: only tris) and let them fall without any goal onto a plane
|
||
(how to set up collision is shown on the page :doc:`Collisions </physics/soft_body/collision>`).
|
||
|
||
.. _fig-softbody-force-interior-without:
|
||
|
||
.. list-table:: Without Stiff Quads.
|
||
|
||
* - .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-001.png
|
||
:width: 200px
|
||
|
||
Frame 1.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-036.png
|
||
:width: 200px
|
||
|
||
Frame 36.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-401.png
|
||
:width: 200px
|
||
|
||
Frame 401.
|
||
|
||
In Fig. :ref:`fig-softbody-force-interior-without`, the default settings are used (without *Stiff Quads*).
|
||
The "quad only" cube will collapse completely, the cube composed of tris keeps its shape,
|
||
though it will deform temporarily because of the forces created during collision.
|
||
|
||
.. _fig-softbody-force-interior-with:
|
||
|
||
.. list-table:: With Stiff Quads.
|
||
|
||
* - .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-001.png
|
||
:width: 200px
|
||
|
||
Frame 1.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-sq-036.png
|
||
:width: 200px
|
||
|
||
Frame 36.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-sq-401.png
|
||
:width: 200px
|
||
|
||
Frame 401.
|
||
|
||
In Fig. :ref:`fig-softbody-force-interior-with`, *Stiff Quads* is activated (for both cubes).
|
||
Both cubes keep their shape, there is no difference for the red cube,
|
||
because it has no quads anyway.
|
||
|
||
|
||
Bending Stiffness
|
||
-----------------
|
||
|
||
The second method to stop an object from collapsing is to change its *Bending* stiffness.
|
||
This includes the diagonal edges (damping also applies to these connections).
|
||
|
||
.. _fig-softbody-force-interior-bending:
|
||
|
||
.. list-table:: Bending Stiffness.
|
||
|
||
* - .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-001.png
|
||
:width: 200px
|
||
|
||
Frame 1.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-bs-036.png
|
||
:width: 200px
|
||
|
||
Frame 36.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-sb-bs-401.png
|
||
:width: 200px
|
||
|
||
Frame 401.
|
||
|
||
In Fig. :ref:`fig-softbody-force-interior-bending`, *Bending* is activated with a strength setting of 1.
|
||
Now both cubes are more rigid.
|
||
|
||
.. list-table::
|
||
|
||
* - .. figure:: /images/physics_soft-body_forces_interior_quadvstri-bending-001.png
|
||
:width: 200px
|
||
|
||
Two planes going to collide.
|
||
|
||
- .. _fig-softbody-force-interior-no-bending:
|
||
|
||
.. figure:: /images/physics_soft-body_forces_interior_quadvstri-bending-101.png
|
||
:width: 200px
|
||
|
||
No bending stiffness.
|
||
|
||
- .. figure:: /images/physics_soft-body_forces_interior_quadvstri-bending-high-101.png
|
||
:width: 200px
|
||
|
||
High bending stiffness (10).
|
||
|
||
Bending stiffness can also be used if you want to make a subdivided plane more plank like.
|
||
Without *Bending* the faces can freely rotate against each other like hinges
|
||
Fig. :ref:`fig-softbody-force-interior-no-bending`.
|
||
There would be no change in the simulation if you activated *Stiff Quads*,
|
||
because the faces are not deformed at all in this example.
|
||
|
||
Bending stiffness is the strength needed for the plane to be deformed.
|