Blender Git Loki

Added a bool return to the eval function to give feedback on invalid
samples.

Skeleton code for sampling meshes.

Merge branch 'master' into hair_system

Bending forces and damping for hair.

This adds some stiffness to hairs along bends, such that the hair does
no longer behave like a chain of freely rotating segments.

Note that there is no bending force on the root segment yet, which means
the hair swivels around the root point without resistance.

Precomputation of rest "bend" vectors in the solver data.

These vectors determine the bending amount of the hair, by giving a
fixed reference from the rest position. The same calculation is done
for the state vectors in every step, but the precomputation saves
roughly half of the cost by avoiding a useless loop over the rest data.

Removed the unused is_dynamic property from solver points.

For the solver data it is quite important to keep the data structs
small, much more than in the DNA data.

Transform3 type for pure rotational matrices.

Implemented hair frame calculation using parallel transport along
curve segments.

This can be done on-the-fly but rotating the root hair frame
incrementally according to each hair segment angle. Note: a similar
approach can be found in the Blender curve code for calculating twist
vectors.

A novel feature of the hair frame calculation is the use of smoothed
hair curves. This prevents artifacts in case of sharp segment angles by
removing small-scale noise from the curve.

Revert "Bake-API: use size_t instead of width, height"

This reverts commit 1607bcebc65fd5296f9f695e76580a1ae7ade9a2.

Bake-API: use size_t instead of width, height

* Original patch by Sergey Sharybin
* Current patch includes function to estimate a width/height when baking into multiple images

Attempt to Fix T41222 Blender gives weird ouput when baking (4096*4096) resolution on GPU

Reviewers: sergey

Subscribers: RadiationG0D

Maniphest Tasks: T41222

Differential Revision: https://developer.blender.org/D688

Merge remote-tracking branch 'origin/master' into testbuild

Revert "Squashed commit of current WIP custom split normals work."

This reverts commit f8cbd0006e5e5bf1e76c378529cda9acef099bba.

Stretch spring damping implementation.

This adds viscous damping to the stretching springs. Note that this does
not yet entirely remove the energy from the system: for this we first
need to implement the bending springs as well, which act based on
angles between hair segments.

Use the actual gravity from the scene for the hair simulation.

A new solver struct for forces has been added, this is supposed to
organize all the external influences in some consistent way.

Simulate hair in world space.

Object space is used for the DNA data, which is more suitable for tools
and object handling. For the simulation though, world space is much
better since calculating forces becomes a lot easier. Otherwise one
would have to take into account "virtual" forces generated by the
accelerated object frame of reference.

Fixed a bug of the simulation stepping loop that caused excessive
increase of the overall step.

Added an operator for resetting hairs to their rest positions.

Implemented stretch springs for hairs based on rest length of segments.

This is still totally undamped and so will start to accumulate energy
quite quickly!

The default parameters (taken from the original paper) probably require
some tweaking, but the overall result can only be judged once the other
main forces are implemented (in particular damping).

Added a HairParams struct to collect all the physical parameters of
hair simulation in one place.

This defines user-settable parameters for controlling things like
stretch stiffness, damping, etc. The defaults of these parameters
should give usable results right from the start (possibly with presets),
but tweaking may still be necessary.

Introduced a rest position vector to hair points.

This defines the "natural" shapes of a hair when no external forces are
acting on it and the velocity is zero. The internal elastic forces of
the hair will cause it to always return to this rest position if
possible.