Fluid: Updated Mantaflow source files

This update introduces two improvements from the Mantaflow repository:

(1) Improved particle sampling:
- Liquid and secondary particles are sampled more predictably. With all parameters being equal, baked particles will be computed at the exact same position during every bake.
- Before, this was not guaranteed.

(2) Sparse grid caching:
- While saving grid data to disk, grids will from now on be saved in a sparse structure whenever possible (e.g. density, flame but not levelsets).
- With the sparse optimization grid cells with a value under the 'Empty Space' value (already present in domain settings) will not be cached.
- The main benefits of this optimization are: Smaller cache sizes and faster playback of simulation data in the viewport.
- This optimization works 'out-of-the-box'. There is no option in the UI to enable it.
- For now, only smoke simulation grids will take advantage of this optimization.

1 files changed, 8 insertions, 2 deletions

diff --git a/extern/mantaflow/preprocessed/particle.cpp b/extern/mantaflow/preprocessed/particle.cpp
index 05c561e2c60..ad1c344d307 100644
--- a/extern/mantaflow/preprocessed/particle.cpp
+++ b/extern/mantaflow/preprocessed/particle.cpp
@@ -28,9 +28,15 @@
 using namespace std;
 namespace Manta {
 
-ParticleBase::ParticleBase(FluidSolver *parent)
-    : PbClass(parent), mMaxParticles(0), mAllowCompress(true), mFreePdata(false)
+int ParticleBase::globalSeed = 9832;
+
+ParticleBase::ParticleBase(FluidSolver *parent, int fixedSeed)
+    : PbClass(parent), mMaxParticles(0), mAllowCompress(true), mFreePdata(false), mSeed(fixedSeed)
 {
+  // use global random seed if none is given
+  if (fixedSeed == -1) {
+    mSeed = globalSeed;
+  }
 }
 
 ParticleBase::~ParticleBase()