[Soc-2017-dev] Weekly Report #08 - Mantaflow Particles and Fluid Guiding

[Sebastián Barschkis]

Hello everyone,

my weekly fluids update is now online:

https://wiki.blender.org/index.php/User:Sebbas/GSoC_2017/Reports/Week_8

= Week 8 =

In this eighth week I mainly worked on secondary particles again. Some
bugs, such as the velocity extrapolation bug, were also on my list.

=== What's been done ===

* What last week was just possible in Mantaflow itself is now possible
inside Blender as well: Drop, bubble and float particles can be enabled
from the "Fluid Particles" tab.

* I improved drop and bubble particles in the sampling function a little
more. Bubbles now take surrounding fluid velocity into consideration (and
so don't just rise straight up). Drop particles are only generated if the
angle between velocity and surface normal doesn't exceed a given threshold
(the "Spray Foam Bubbles" paper from Ihmsen et al. suggested this nice
approach).

* The first version for tracer particles is up and running.

* Setting outflow cells is now done with "initDomain()". Previously by
using "setOpenBound()", we got a one cell margin between FLIP particles and
actual outflow (and thus particles never got reset!).

* Regarding the velocity extrapolation bug: I didn't fix it yet but made
some progress in terms of what's causing it (check out Github for more
info). I also fixed a related issue in this context. The outermost outflow
cells, which now get set with "initDomain()", weren't updated when one
manually placed an obstacle object near the border. A small change in
"updateFromLevelset" fixed this issue.

* Smaller bug fixes (including a Windows easter egg :) The define PFLOAT,
which I used for the float particle type, had already been defined in a
Windows header ...)

=== Next up ===

* Revisit the particle sampling function: Expose more arguments to the UI
(tracer amount field still needs some work) and optimize a bit (currently
each particle type has its own loop - it should be possible to combine
some.)

* Take a closer look at Mantaflows fluid guiding setup. I'll start very
simple and try to run one of the existing sample scripts in Blender.

* The velocity extrapolation bug remains. Nils pointed out some parts in
one of Mantaflows velocity extrapolation functions that might cause
problems. What I'll now do is, since I couldn't fix the bug in Blender
directly, setup a Mantaflow scene that also produces the issue.

=== Questions ===

* No

Best wishes,
Sebastián
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