This is more involved than using simple straight bending targets
constructed from the neighboring segments, but necessary for restoring
groomed rest shapes.
The targets are defined by parallel-transporting a coordinate frame
along the hair, which smoothly rotates to avoid sudden twisting (Frenet
frame problem). The rest positions of hair vertices defines the target
vectors relative to the frame. In the deformed motion state the frame
is then recalculated and the targets constructed in world/root space.
The hair solver needs sane input to converge within reasonable time
steps. In particular the spring lengths must not be too difference
(factor 0.01..100 or so max, this is comparable to rigid body simulation
of vastly different masses, which is also unstable).
The basic hair system generate strands with equally spaced points, which
is good solver material. However, the hair edit operators, specifically
the cutting tool, can move points along the strands, creating tightly
packed hair points. This puts the solver under enormous stress and
causes the "explosions" observed already during the Sintel project.
The simple solution for now is to exclude very short hairs from the
simulation. Later the cutting tool should be modified such that it
keeps the segments roughly at the same length and throws away vertices
when the hair gets too short (same goes for the extension tool).
The hair system should have a general mechanism for making sure that
situations such as this don't occur. This will have to be a design
consideration for replacements in any future hair system.
This adds transformations for each hair from world to "root space".
Currently positions and velocities are simply transformed for the solver
data and inverse-transformed when copying the results back to the cloth
data. This way the hair movement becomes independent from the movement
of the emitter object. Eventually the "fictitious" forces originating
from emitter movement can be added back in a controlled way.
http://en.wikipedia.org/wiki/Fictitious_force
Ignoring these fictitious forces or scaling their effect is physically
correct, because in the absence of external forces the hair will always
return to rest position in this root frame.
External forces currently are not yet transformed into the root space.
This will allow us to implement moving reference frames for hair and
make "fictitious" forces optional, aiding in creating stable and
controllable hair systems.
Adding data in this place is a nasty hack, but it's too difficult to
encode as a DM data layer and the whole cloth modifier/DM intermediate
data copying for hair should be removed anyway.
This is still using the old BVH tree collision methods to generate
contact points, similar to what cloth does. This should be replaced
by a Bullet collision check, but generating contacts in this way is
easier for now, and lets us test responses and stability (although in
more complex collision cases the BVH method fails utterly, beside being
terribly inefficient with many colliders).
In rB78c491e the `initialize_particle` function was split into 2 parts for particle texture initialization.
The texture init part however also initializes birth times, which is now missing in the main init function
in some cases (notably when setting start/end directly without a subsequent time step).
Fluid sims have a very nasty feature for interaction, in which a psys
can directly update the bvhtree for //another object's psys//. This
breaks with threaded depsgraph evaluation and is generally a no-go.
To avoid crashes for now, use a global mutex to avoid concurrent writes
to an object psys' bvhtree.
in threaded depgraph updates and effector list construction.
Gathering effectors during depgraph updates will call the
psys_check_enabled function. This in turn contained a DNA alloc call
for the psys->frand RNG arrays, which is really bad because data must be
immutable during these effector constructions.
To avoid such allocs the frand array is now global for all particle
systems. To avoid correlation of pseudo-random numbers the psys->seed
value is complemented with random offset and multiplier for the actual
float array. This is not ideal, but work sufficiently well (given that
random numbers were already really limited and show repetition quite
easily for particle counts > PSYS_FRAND_COUNT).
updates.
This file crashes on loading with NULL pointer access to curve_cache:
{F77132}
The pdInitEffectors function was amalgamating the simple
collection of effector objects with an automatic precalculation for
curve guides and the like. This precalculation requires object data
that may not be available until the DAG has finished.
Since for DAG dependencies only the list of effectors is required,
added an argument to disable precalculation when collecting effectors.
Root of the issue goes to the order of particle initialization which does
texture evaluation (which does depend on particle coordinate) and particle
birth coordinate calculation. So basically what happened is:
* Changing number of particles re-allocated all the particles,
which sets their coordinate to (0,0,0)
* Texture evaluation used this non-initialized coordinate
* Coordinates were calculated for particles
Reshuffled code a bit so now texture evaluation happens after particles.
coordinate calculation. Basically moved texture evaluation to particle
reset function. Reset happens after initialization anyway and it does
know particle coordinates. Also, if reset is being called without init
then it's also kind of logical to re-evaluate texture because particle
coordinates might change.
(@plasmasolutions): When the particle emitter is parented to a fast
moving object, the emission locations will not be interpolated over
subframes. This works if the particle emitter is animated itself.
Particle system evaluates the emitter location for each subframe, but
has to do this for the parent objects as well to get reliable results.
accesses the particle lifetime/dietime data before it is actually defined! This is a design flaw, but to avoid corrupted data for now just initialize the lifetime/dietime values for particles in advance
before evaluating the texture.
Problem was introduced with r54648, which determined the initial interval for the Newton-Raphson method using the "total_time" of the collision - but this info is only defined for regular collisions, not
for the raycasting used in boids to find the "ground object". To ensure correct behavior, now clear the collision info before using it (good practice in any case), then check the inv_total_time variable
and use the standard 0.001 step if not defined.
Particle system code used global variable to sort hair by orig index,
which is not safe for threading at all.
Replaced this with usage of reentrant version of qsort, which is
now implemented in BLI. It was moved from recast navigation code
to BLI, so more areas could use it (if needed).
--
svn merge -r59086:59087 ^/branches/soc-2013-depsgraph_mt
Lattice deformation used to store some runtime data
inside of lattice datablock itself. It's something
which is REALLY bad. Ideally DNA shouldn't contain
and runtime data.
For now solved it in a way that initialization of
lattice deform will create a structure which contains
lattice object for which deformation is calculating
and that runtime data which used to be stored in
lattice datablock itself.
It works really fine for mesh deform modifier, but
there's still runtime data stored in particle system
DNA, It didn't look something easy to be solved, so
leaving this as-is for now.
--
svn merge -r58277:58278 -r58795:58796 ^/branches/soc-2013-depsgraph_mt
With deformations and on a simple cube you could get axis flipping with normal-particle alignment.
now use the normal & tangent to create the orientation to give a stable matrix that wont flip.
rendering. This used to happen in an unneeded frame change update which was
removed. For heavy particle systems this could have a bad impact on viewport
performance after rendering.
