Blender Git Loki

Fix T60607: Spin tool duplicates after Spin Duplicate

Cleanup: pep8 for examples

Cleanup: correct logical error in last commit

Worked because: -INT_MIN == INT_MIN

Cycles: Fixes for spectral MIS volume tracking.

Cycles: Implemented more unbiased volume trackers:

* Woodcock tracking
* Weighted tracking
* Spectral tracking

Cycles: Added volume integrator to integrator node.

Cycles: Added tracking based Volume integrator.

Implementing Novak et al's Residual Ratio Tracking and Szirmay-Kalos
et al's unbiased tracker.

Sequencer: use all selected strips for select side operator

D6127 by @a.monti with edits.

Merge branch 'blender-v2.81-release'

Fix inability to toggle pose-mode without sync-selection

- There was no way to select some kinds of data without activating them.
- Pose mode could not be activated at all.

No change to behavior with sync-selection enabled.

Merge branch 'feature/modifier_openvdb_280' into blender-v2.80-develop

OpenVDB: Fixed "Hide Unselected" option.

GPencil: Add missing prop Update

Transform: Add option to exclude back facing geometry from snapping

Add new `Backface Culling` option to the snapping properties.
This option has nothing to do with the view3d display or the
workbench `Backface Culling` option.

Limitation:
- In edit mode, this option only affects snap to faces.

Maniphest Tasks: T71217

Differential Revision: https://developer.blender.org/D6155

GPencil: Set Active Smooth to 0.35

With new design of sampling, the old value was too high.

GPencil: Double Random Pressure effect

GPencil: Remove Smooth Thickness and Randomness

These parameters are not needed with the new functions.

Allow deselecting individual handles & keys with ctrl+box select

Merge branch 'master' into greasepencil-object

GPencil: Add Mix color to paint operators