* Particle emission now updates all parent objects too to the exact emission time.
* This only does object level animation as updating the object data for every particle would be too slow.
* A better fix could be to interpolate the emission location directly from the current particle emission location and the location from the previous frame, but for this some point cache changes have to be made, so it will have to wait.
* The old collisions code detected particle collisions by calculating the
collision times analytically from the collision mesh faces. This was
pretty accurate, but didn't support rotating/deforming faces at all, as
the equations for these quickly become quite nasty.
* The new code uses a simple "distance to plane/edge/vert" function and
iterates this with the Newton-Rhapson method to find the closest particle
distance during a simulation step.
* The advantage in this is that the collision object can now move, rotate,
scale or even deform freely and collisions are still detected reliably.
* For some extreme movements the calculation errors could stack up so much
that the detection fails, but this can be easily fixed by increasing the
particle size or simulation substeps.
* As a side note the algorithm doesn't really do point particles anymore,
but uses a very small radius as the particle size when "size deflect" isn't
selected.
* I've also updated the collision response code a bit, so now the particles
shouldn't leak even from tight corners.
All in all the collisions code is now much cleaner and more robust than before!
the same, but big changes have happened both on the outside and on the inside.
New UI:
* The old parameters were quite true to the underlying algorithm, but were quite obscure
from a users point of view. Now there are only a few intuitive basic parameters that
define the basic fluid behavior.
** By default particle size is now used to determine the interaction radius, rest
density and spring rest lengths so that it's easy to get stable simulations by simply
emitting particles for a few frames and adjusting the particle size (easy when the
particle size is drawn) so that the fluid appears continuous (particles are touching
eachother).
** Stiffness - in reality most fluids are very incompressible, but this is a very hard
problem to solve with particle based fluid simulation so some compromises have to be
made. So the bigger the stiffness parameter is the less the fluid will compress under
stress, but the more substeps are needed for stable simulation.
** Viscosity - how much internal friction there is in the fluid. Large viscosities also
smooth out instabilities, so less viscous fluids again need more substeps to remain
stable.
** Buoancy - with high buoancy low pressure areas inside the fluid start to rise against
gravity, and high pressure areas start to come down.
* In addition to these basic parameters there are separate advanced parameters that can
either be tweaked relative to the basic parameters (or particle size) or defined
independently.
** Repulsion - the stiffness parameter tries to keep the fluid density constant, but this
can lead to small clumps of particles, so the repulsion keeps the particles better
separated.
** Stiff viscosity - the normal viscosity only applies when particles are moving closer to
eachother to allow free flowing fluids. Stiff viscosity also applies smoothing to
particles that are moving away from eachother.
** Interaction radius - by default this is 4 * particle size.
** Rest density - by default this is a density that the particles have when they're packed
densely next to eachother.
** Spring rest length - by default this is 2 * particle size.
* There are also new options for 3d view particle coloring in the display panel to show
particle velocity and acceleration. These make it easier to see what's happening in the
fluid simulations, but can of course be used with other particles as well.
* Viscoelastic springs have some new options too. The plasticity can now be set to much
higher values for instant deletion of springs as the elastic limit is exeeded. In addition
to that there is an option to only create springs for a certain number of frames when a
particle is born. These options give new possibilities for breaking viscoelastic fluids.
New in the code:
* Most of the fluids code is now thread safe, so when particle dynamics go threaded there
will be a nice speed boost to fluids as well.
* Fluids now use a bvh-tree instead of a kd-tree for the neighbor lookups. The bvh-tree
implementation makes the code quite a bit cleaner and should also give a slight speed
boost to the simulation too.
* Previously only force fields were calculated with the different integration methods, but
now the fluid calculations are also done using the selected integration method, so there
are again more choices in effecting simulation accuracy and stability. This change also
included a nice cleanup of the whole particle integration code.
As the internals are pretty stirred up old particle fluid simulations will probably not
work correctly straight away, but with some tweaking the same level of control is still
available by not using the "relative versions" of the advanced parameters (by default these
are not used when loading old files).
* Grid distribution isn't really suited for hair, so this is now disabled.
* Setting a jittered distribution with particles/face = 1 now creates particles on the center of faces.
* Quite a bit of cleanup of the whole particle distribution code.
* In some cases fluid particles could be born at the exact same locations. Now these cases are just ignored and such particles don't effect each other.
* New option to distribute particles in a hexagonal grid.
* This is much more stable for fluids than normal grid distribution and looks quite nice otherwise too :)
* Also some small scale code cleanup of grid distribution code.
- use NULL rather then 0 where possible (makes code & function calls more readable IMHO).
- set static variables and functions (exposed some unused vars/funcs).
- use func(void) rather then func() for definitions.
* Effecting particle properties with textures was possible in 2.49,
but not in 2.5 anymore.
* Now particles have their own textures (available in texture panel
for objects with particle systems), which are totally separate from
the material textures.
* Currently a basic set of particle properties is available for
texture control. Some others could still be added, but the whole
system is not intended as an "change anything with a texture" as
this kind of functionality will be provided with node particles in
the future much better.
* Combined with the previously added "particle texture coordinates"
this new functionality also solves the problem of animating particle
properties through the particle lifetime nicely.
* Currently the textures only use the intensity of the texture in
"multiply" blending mode, so in order for the textures to effect
a particle parameter there has to be a non-zero value defined for
the parameter in the particle settings. Other blend modes can be
added later if they're considered useful enough.
* Particles that aren't shown are now actually deleted (huge memory savings for flat objects).
* Grid distribution for flat objects is now done on the surface object surface without offset.
* Invert grid option wasn't in ui and it didn't work for non-volume grids.
* New parameter to randomize the grid point locations.
* Resolution soft/hard limits changed to even 50/250.
* When a simulation is baked no dynamics calculations should happen anymore (even outside of baked frame range) since these can be very time consuming and baked simulations are supposed to be fast!
* Viscoelastic springs between the fluid particles can simulate all kinds
of viscous and elastic substances, such as jelly and honey. This is
achieved by creating springs dynamically between neighboring particles
and adjusting their rest length based on stretching/compression.
* This nearly completes the currently intended functionality for particle
fluids. The last missing thing is a surfacing extraction algorithm,
which is needed for a proper representation of a sph fluid.
* I also cleaned up and renamed some of the fluid parameters to make the
ui a bit easier to understand.
* One addition to the patch is an option to use "initial rest length" for
the springs, which uses the lengths between the particles at the time of
spring creation as the spring rest lengths instead of interaction radius/2.
This makes the fluid keep it's original shape better (good for very
viscoelastic materials), but can create large density differences inside
the fluid (not really physically correct for a fluid).
* Viscoelastic springs are stored in point cache as extra data.
* Renamed children to "simple" and "interpolated" as this is
easier to explain and more descriptive than "from particles"
and "from faces".
* Also shuffled the child ui around a bit to make it clearer.
* Child seed parameter allows to change the seed for children
independent of the main seed value.
* Long hair mode for interpolated children:
- Making even haircuts was impossible before as the child
strand lengths were even, but their root coordinates were
not similar in relation to the parent strands.
- The "long hair" option uses the tips of the parent strands
to calculate the child strand tips.
* Hair parting options:
- Hair parting can now be calculated dynamically on the fly
when in 2.49 there was a cumbersome way of using emitter mesh
seams to define parting lines.
- For long hair parting can be created by a tip distance/root
distance threshold. For example setting the minimum threshold
to 2.0 creates partings between children belonging to parents
with tip distance of three times the root distance
((1+2)*root distance).
- For short hair the parting thresholds are used as angles
between the root directions.
* New kink parameters:
- Kink flatness calculates kink into a shape that would have
been achieved with an actual curling iron.
- Kink amplitude clump determines how much the main clump value
effects the kink amplitude.
- The beginning of kink is now smoothed to make the hair look
more natural close to the roots.
* Some bugs fixed along the way too:
- Child parent's were not determined correctly in some cases.
- Children didn't always look correct in particle mode.
- Changing child parameters caused actual particles to be
recalculated.
* Also cleaned up some deprecated code.
All in all there should be no real changes to how old files look
(except perhaps a bit better!), but the new options should make
hair/fur creation a bit more enjoyable. I'll try to make a video
demonstrating the new stuff shortly.
* Two separate bugs, with very similar symptoms.
* The distribution binary search didn't work correctly in cases where there were a lot of faces with 0 weights.
* Maximum distribution sum should have been exactly 1, but due to the wonderful nature of floats this wasn't the case at all.
* Massive reorganization of pointcache code, things are now cleaner than ever.
* For all but smoke the cache is first written to memory when using disk cache and after that written to disk in one operation. This allows less disk operations and the possibility to compress the data before writing it to disk.
* Previously only smoke cache could be compressed, now the same options exist for other physics types too (when using disk cache). For now the default compression option is still "no compression", but if there aren't any problems this can be set to "light compression" as it's actually faster than no compression in most cases since there's less data to write to the disk. Based on quick tests heavy compression can reduce the file size down to 1/3rd of the original size, but is really slow compared to other options, so it should be used only if file size is critical!
* The pointcache code wasn't really 64bit compatible (for disk cache) until now, so this update should fix some crashes on 64bit builds too. Now all integer data that's saved to disk uses 32 bit unsigned integers, so simulations done on 64bit should load fine on 32bit machines and vice versa. (Important disk cache simulations made on 64bit builds should be converted to memory cache in a revision before this commit).
* There are also the beginnings of extradata handling code in pointcache in anticipation of adding the dynamic springs for particle fluids (the springs need to be stored as extradata into point cache).
* Particles were being read from the cache with a slightly wrong framerate. In most cases this probably wasn't noticeable, but none the less the code is now correct in every way.
* Small other fixes here and there & some cosmetic changes to cache panel, but over all there should be no functional changes other than the new disk cache compression options.
* This whole re-organization also seems to fix bug #25436 and hopefully shouldn't introduce any new ones!
* Pointcache code was quite ugly looking and complicated, so here are mostly just cosmetic adjustments, but some improved logic also.
* Slight cleanup of pointcache ui too.
* Shouldn't have any functional changes what so ever, so poke me right away if something seems off.
* Depsgraph wasn't updated properly for smoke flow collision object dependencies.
* Smoke also wasn't properly using the actual emission frame of the flow particles.
* There was a lot of bloated logic in some parts of particle code so this fix turned into a small scale cleanup operation.
** As a result particle updating and cache usage should be a bit more stable too.
* New option to "Regrow hair" for each frame.
* This was perhaps more a feature request, but there was a similar useful feature called "animated hair" in particles at some point.
* The previous behavior for hair growing was inconsistent to say the least, so this is a nice option to have.
* Calling update_children(..) is very light if there's nothing to update, so it doesn't matter if it's called every time the particle system is updated.
