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 a bug where volumes straddling camera's far clip plane could sometimes cause render to hang.

Fixed a bug in the Trace SOP that resulted in stretched results when using a volume wider than it is tall.

The karma:light:shader parameter was changed from a string to an asset to allow the asset resolver to kick in for evaluation.

Fix a bug with hkey that incorrectly reported expired dates if the date was past 2037.

Improvements for the Edit Context Options dialog:

• "Automatic" context options are hidden by default
• User created context options can be explicitly marked as "hidden"

A settings menu provides toggle to turn on the display of each of these types of initially hidden context options.

Fixed a problem that could cause HARS to randomly shut down when cooking a PDG graph.

The Remesh to Camera SOP should now properly convex input geometry to triangles before subdividing.

Fixed a rare crash when recooking a graph with multiple consecutive partitioner nodes, without dirtying any of the nodes between cooks.

The Remesh to Camera SOP, which subdivides input geometry to generate polygons smaller than a camera measurement, is now available in 19.5.

Fixed an exception when querying work item data from the job environment with RPC data source option enabled.

Fixed a performance issue with building locked stages for nodes such as the LOP Import SOP, when the source stage had many sublayers.

Fixed an issue that kept Houdini from starting on systems built with glibc 2.39.

Make further file system performance improvements for HOUDINI_VDB_FORCE_STREAM_SAVE by increasing its buffer size to 128 KB blocks.

Add HOUDINI_VDB_FORCE_STREAM_SAVE environment variable. When enabled, this forces .vdb files to be saved via a file stream that disables the ability to perform delayed loading on the saved .vdb files. This can improve file write performance by avoiding file seeking. Notably, Qumulo file systems suffer from this (but not Isilon file systems).

Fixed an issue with PDG throwing an exception on initialization when the `future` package is installed on the Python path.

Fixed thread safety issue when calling HAPI_IsSessionValid from multiple threads.

Fixed an issue where the output from HAPI was not being redirected to the Output Window properly.

Fix an issue where context option changes might not cause nodes to recook when first loading a hip file with delay-loaded HDAs.

Added support for setting an explicit alpha value on a netbox.

Modified hython so that it does not preconfigure the Qt environment by setting QT_PLUGIN_PATH and QT_QPA_FONTDIR if those variables already exist in the environment. This enables users to specify their own Qt environment to use in hython instead of the one in $HFS.

Fixed a warning when using landscapes with the old Unreal input system.

Fixed a crash during cooking if an HDA input straddles a world partition boundary.

Limit the number of Landscape Splint control points input from Houdini to Unreal to 1000. This prevents a crash in Unreal when saving a map with a high number of control points.