Fixed hanging in Houdini related to Python SOP nodes. For example, Houdini would hang when cooking Python SOP nodes from Houdini Engine Session Sync, or when a background thread tried to call into HOM while Houdini cooked Python SOP nodes.

The fix required restoring old behavior in Python SOP nodes that unfortunately reintroduces an old hang, one at least that is limited in scope. The old hang occurs when Python SOP nodes execute multi-threaded code that calls into the HOM `hou` package from separate threads. If you wish to run such code in Python SOPs, then you can set `HOUDINI_ALLOW_PYTHON_SOP_MULTITHREADING=1` in the environment with the caveat that you may encounter other hangs as detailed above (i.e. cooking Python SOP nodes from Session Sync).

Fixed an issue where some versions of the colormap/rawcolormap functions weren't handling variadic arguments properly. This may cause results of these functions to change if there were variadic arguments in use before.

Fix regression between Remesh-1.0 and Remesh-2.0 and Houdini versions 18.5 and 19.0 where Remesh-2.0 could cause errosion along boundaries when using adaptive remeshing with several iterations.

Fixed an issue in the MuscleSolverVellum and MuscleConstraintProperties nodes, where using negations in the muscle-to-muscle attachment candidate strings could lead to self-referencing constraint attachments.

XPU: Fixed a bug with attributes (including UVs) being evaluated distorted on n-gons that are not subdivided but have displacement.

The Open Subdiv subdivide SOP with T-junctions will now convex the same way as the Divide SOP so should avoid cases of missing polygons or wrong-sided polygons. This will change the vertex/primitive order coming out of this SOP.

Shaders using Mtlx Height to Normal nodes may appear slightly different.

Fixed a bug in Poly Extrude 2.0 where division have artifacts and polygons are sheared.

Smoother filtering in displacement shaders by compensating for discontinuous jump in density between adjacent grids. Note that this change only applies when the environment variable KARMA_DICING_LEGACY is set to 0.

Added an optimization to SOP Merge Field DOP for vector VDBs whose voxels are an integer offset away from the destination field's. This may change results of pyro and FLIP simulations.

Gas Resize Field may produce results that are a little numerically different from before. In particular, locations of the fields are fixed to ensure that voxel boundaries are as close as possible after resizing. Notably, this affects all pyro and FLIP simulations.

husd.utils.getMetersPerUnit will now return the USD default rather than the Houdini setting when queried against a stage that does not explicitly author a value for the metersPerUnit metadata.

Muscle to Muscle Sliding has been exposed in the properties node parameters, and is now supported in the muscle solver. Muscle to bone Tangent Stiffness, and Muscle to Muscle Compress Stiffness have had some fixes made. Due to these changes, resulting sims may have minor differences as of this release.

Fixed a bug where emissive objects with "Treat As Light Source" enabled were using the wrong LPE token ('O' instead of 'L') on primary ray hits.

The Subdivide SOP in the OpenSubdiv modes will properly subdivide a partial group when non-polygonal inputs are present.

Replaced the default generated copy constructor and assignment operator on GA_PrimitiveTypeMask with ones that work correctly, which required bumping the HDK ABI version.

When using a SOP Modify LOP (or other means of using the Unpack USD SOP) geometry), a mesh's displayOpacity USD primvar will now be renamed to Alpha in SOPs, complementing the existing displayColor -> Cd renaming.

Bumped the HDK ABI version due to changes in HOM that affect ABI compatibility.

Bumped the HDK ABI version due to changes in HOM that affect ABI compatibility.

Further to the change in 19.5.582, the Instancer LOP now treats 3-float SOP data with no type qualifier as "float3"/"double3" when generating USD attributes, rather than the previous "vector3f"/"vector3d". If you require "vector3f"/"vector3d" USD types, you must now explicitly set a "vector" type qualifier in SOPs.