Field3D v1.7

[Magnus Wrenninge]

The master branch was just moved to point to v1.7, which has been used in production here at Pixar for the last round of shows (The Good Dinosaur and Finding Dory). 

Here are some of the new features:

Thread safe I/O

Field3D now performs internal locking to make file I/O thread safe. It is now fine to read from multiple files on multiple threads.

Ogawa-based files

A new back-end to replace HDF5, based on the Ogawa library that powers Alembic. I/O is much faster with Ogawa, and compression/decompression of data (which is the #1 bottleneck) is now multi-threaded.

Field3D is fully backwards compatible and will read and write both HDF5 and Ogawa files. By default, files are written in the Ogawa format, but this can be controlled using Field3DOutputFile::useOgawa().

Min/Max generation

In order to interface with the latest path tracing renderers, Field3D's f3dmakemip utility can now generate hierarchical min/max representations that the FieldGroup class will recognize and utilitize in order to quickly respond to getMinMax() queries.

Consistent voxel placement for MIP fields

Version 1.6 produced MIP fields that would shift in space if the source data had animating bounds. In 1.7, this has been fixed, and a 'mipoffset' metadata integer is recorded in each file to ensure that data is consistent for animations.

FieldCache

For applications that repeatedly load the same field, an automatic caching mechanism will now detect if a field that was previously loaded is still available in memory, and if so, will return a pointer instead of loading the data from disk.

Magnus