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This implements angular bending springs for cloth simulation. This also
adds shearing springs for n-gons.
This angular spring implementation does not include Jacobian matrices,
as the springs can exist between polygons of different vertex counts,
rendering their relationships asymmetrical, and thus impossible to solve
with the current implementation. This means that the bending component
is solved explicitly. However, this is usually not a big problem, as
bending springs contribute less to instability than structural springs.
The the old linear bending model can still be used, and is the default for
existing files, to keep compatibility. However, the new angular bending
model is the default for any new simulation.
This commit makes small breaking changes, in that shearing springs are
now created on n-gons (also in linear bending mode), while n-gons were
previously ignored.
Reviewed By: brecht
Differential Revision: http://developer.blender.org/D3662
This separates cloth stiffness and damping forces into tension,
compression, and shearing components, allowing more control over the
cloth behaviour.
This also adds a bending model selector (although the new bending model
itself is not implemented in this commit). This is because some of the
features implemented here only make sense within the new bending model,
while the old model is kept for compatibility.
This commit makes non-breaking changes, and thus maintains full
compatibility with existing simulations.
Reviewed By: brecht
Differential Revision: http://developer.blender.org/D3655
Brecht authored this commit, but he gave me the honours to actually
do it. Here it goes; Blender Internal. Bye bye, you did great!
* Point density, voxel data, ocean, environment map textures were removed,
as these only worked within BI rendering. Note that the ocean modifier
and the Cycles point density shader node continue to work.
* Dynamic paint using material shading was removed, as this only worked
with BI. If we ever wanted to support this again probably it should go
through the baking API.
* GPU shader export through the Python API was removed. This only worked
for the old BI GLSL shaders, which no longer exists. Doing something
similar for Eevee would be significantly more complicated because it
uses a lot of multiplass rendering and logic outside the shader, it's
probably impractical.
* Collada material import / export code is mostly gone, as it only worked
for BI materials. We need to add Cycles / Eevee material support at some
point.
* The mesh noise operator was removed since it only worked with BI
material texture slots. A displacement modifier can be used instead.
* The delete texture paint slot operator was removed since it only worked
for BI material texture slots. Could be added back with node support.
* Not all legacy viewport features are supported in the new viewport, but
their code was removed. If we need to bring anything back we can look at
older git revisions.
* There is some legacy viewport code that I could not remove yet, and some
that I probably missed.
* Shader node execution code was left mostly intact, even though it is not
used anywhere now. We may eventually use this to replace the texture
nodes with Cycles / Eevee shader nodes.
* The Cycles Bake panel now includes settings for baking multires normal
and displacement maps. The underlying code needs to be merged properly,
and we plan to add back support for multires AO baking and add support
to Cycles baking for features like vertex color, displacement, and other
missing baking features.
* This commit removes DNA and the Python API for BI material, lamp, world
and scene settings. This breaks a lot of addons.
* There is more DNA that can be removed or renamed, where Cycles or Eevee
are reusing some old BI properties but the names are not really correct
anymore.
* Texture slots for materials, lamps and world were removed. They remain
for brushes, particles and freestyle linestyles.
* 'BLENDER_RENDER' remains in the COMPAT_ENGINES of UI panels. Cycles and
other renderers use this to find all panels to show, minus a few panels
that they have their own replacement for.
This removes the goal springs, in favor of simply calculating the goal forces on the vertices directly. The vertices already store all the necessary data for the goal forces, thus the springs were redundant, and just defined both ends as being the same vertex.
The main advantage of removing the goal springs, is an increase in flexibility, allowing us to much more nicely do some neat dynamic stuff with the goals/pins, such as animated vertex weights. But this also has the advantage of simpler code, and a slightly reduced memory footprint.
This also removes the `f`, `dfdx` and `dfdv` fields from the `ClothSpring` struct, as that data is only used by the solver, and is re-computed on each step, and thus does not need to be stored throughout the simulation.
Reviewers: sergey
Reviewed By: sergey
Tags: #physics
Differential Revision: https://developer.blender.org/D2514
Note that the collision modifier doesn't have any use for Loop indices,
so to avoid duplicating the loop array too,
MVertTri has been added which simply stores vertex indices (runtime only).
as complicated as before cloth solver changes.
Still doesn't solve the collapsing cloth cube issue mentioned in T43406,
probably the bending springs work somewhat differently now.
This was disabled during the course of hair dynamics work. The cloth
collision solution is based on a secondary velocity-only solver step.
While this approach is usable in general, the collision response
calculation still does not work well for hair meshes. Better contact
point generation is needed here (Bullet) and preferably an improved
solver for unilateral constraints.
These were used as UI buttons during development. If such parameters are
needed again later they should instead be added in the (now global)
SimDebugData and made accessible with a dev addon or so.
This way it doesn't have to be stored as DNA runtime pointers or passed
down as a function argument. Currently there is now no property or
button to enable debugging, this will be added again later.
approach does not work very well.
Using a cross section estimate still causes large oscillations due to
varying hair force based on angles. It also requires a sensible hair
thickness value (particle radius) which is difficult to control and
visualize at this point.
The new model is based purely on per-vertex forces, which seems to be
much more stable. It's also somewhat justified by the fact that each
hair vertex represents a certain mass.
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
The previous calculation was modulated with the angle between the wind
direction and the segments, which leads to very oscillating behavior.
Now the formula includes an estimate for the geometric cross section
of a hair segment based on the incident angle and the hair thickness
(currently just the particle size). This gives a more stable behavior
and more realistic response to wind.
Conflicts:
source/blender/blenkernel/intern/particle_system.c
source/blender/physics/intern/BPH_mass_spring.cpp
to support multiple hash identifiers.
Using explicit hashing functions for every sim debug call defeats the
purpose of having a quick feedback system. Now this can be done simply
by passing an arbitrary number of hash inputs (integers) at the end of
the function calls, which are then combined by a system of variadic
macros (based on the ELEM feature). Up to 8 identifiers are supported
currently, but more could be added easily if needed.
Conflicts:
source/blender/blenkernel/intern/particle_system.c
source/blender/physics/intern/BPH_mass_spring.cpp
This allows setting a target density which the fluid simulation will
take into account as an additional term in the pressure Poisson
equation. Based on two papers
"Detail Preserving Continuum Simulation of Straight Hair" (McAdams et al. 2009)
and
"Two-way Coupled SPH and Particle Level Set Fluid Simulation" (Losasso et al. 2008)
Currently the target pressure is specified directly, but it will be
a lot more convenient to define this in terms of a geometric value such
as "number of hairs per area" (combined with hair "thickness").
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
on the grid.
This uses the Eigen conjugate-gradient solver to solve the implicit
Poisson equation for the pressure Laplacian:
div(grad(p)) = div(v)
As described in "Detail Preserving Continuum Simulation of Straight Hair"
(McAdams, Selle, 2009).
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
This is a bit more awkward for artists to use, but necessary for
a stable solution of the hair continuum calculation. The grid size is
defined by the user, the extent of the grid is then calculated based on
the hair geometry. A hard upper limit prevents bad memory allocation
in case too small values are entered.
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
This is a leftover from previous approach of hair collisions (with
insufficient results). The hair volumetrics actually implements
"collision" with solid objects as well, but uses a Neumann boundary
condition on the main grid for this purpose.
This is based on the paper
"Detail Preserving Continuum Simulation of Straight Hair"
(McAdams, Selle, Ward, 2009)
The main difference is that hair line segments are used rather than only
rasterizing velocity at the vertices. This gives a much better coverage
of the hair volume grid, otherwise gaps can be produced at smaller grid
cell sizes and the distribution is uneven along the hair curve.
The algorithm for rasterizing is a variation of Bresenham's algorithm
extended onto 3D grids.
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
solver step.
Calculating forces and jacobians from linearly interpolated grid values
is problematic due to discontinuities at the grid boundaries. The new
approach of modifying velocities after the backward euler solver step
was suggested in a newer paper
"Detail Preserving Continuum Simulation of Straight Hair"
(McAdams, Selle 2009)
Conflicts:
source/blender/physics/intern/BPH_mass_spring.cpp
This is not necessary: the implicit solver data can keep track instead
of how many off-diagonal matrix blocks are in use (provided the
allocation limit is calculated correctly). Every time a spring is
created it then simply increments this counter and uses the block index
locally - no need to store this persistently.
derivatives for stabilization.
The bending forces are based on a simplified torsion model where each
neighboring point of a vertex creates a force toward a local goal. This
can be extended later by defining the goals in a local curve frame, so
that natural hair shapes other than perfectly straight hair are
supported.
Calculating the jacobians for the bending forces analytically proved
quite difficult and doesn't work yet, so the fallback method for now
is a straightforward finite difference method. This works very well and
is not too costly. Even the original paper ("Artistic Simulation of
Curly Hair") suggests this approach.
This returns a general status (success/no-convergence/other) along with
basic statistics (min/max/average) for the error value and the number
of iterations. It allows some general estimation of the simulation
quality and detection of critical settings that could become a problem.
Better visualization and extended feedback can follow later.
This makes the bending a truely local effect. Eventually target
directions should be based in a local coordinate frame that gets
parallel transported along the curve. This will allow non-straight
rest shapes for hairs as well as supporting twist forces. However,
calculating locally transformed spring forces is more complicated.
These are much better suited for creating stiff hair. The previous
bending springs are based on "push" type spring along the hypothenuse
of 3 hair vertices. This sort of spring requires a very large force
in the direction of the spring for any angular effect, and is still
unstable in the equilibrium.
The new bending spring model is based on "target" vectors defined in a
local hair frame, which generates a force perpendicular to the hair
segment. For further details see
"Artistic Simulation of Curly Hair" (Pixar technical memo #12-03a)
or
"A Mass Spring Model for Hair Simulation" (Selle, Lentine, Fedkiw 2008)
Currently the implementation uses a single root frame that is not yet
propagated along the hair, so the resulting rest shape is not very
natural. Also damping and derivatives are still missing.
single transform matrix.
Dynamic properties of the transformation are only needed during the
setup phase when they should be read from external data (hair system
roots) and generate fictitious forces on each point.
This is part of the original method from "Volumetric Methods for
Simulation and Rendering of Hair". The current filter is a simple box
filter. Other energy-preserving filters such as gaussian filtering
can be implemented later.
The filter size is currently given as a cell count. This is not ideal,
rather it should use a geometrical length value, but this is too
abstract for proper artistical use. Eventually defining the whole grid
in terms of spatial size might work better (possibly using an external
object).
