Bifrost 2.2.0.0 is a feature release with new features, performance improvements, and bug fixes. Some of these features will result in broken connections when older graphs are loaded. Bifrost 2.2.0.0 is included with the installer for Maya 2020.4 Update.

Bifrost 2.2.0.1 is a bug-fix release that addresses some issues in Bifrost 2.2.0.0. It is available for Maya versions 2018.x, 2019.x, and 2020.x from the Autodesk Accounts Portal.

Backward Compatibility Warnings

The new features of this release bring with them a few changes that break backward compatibility with previous versions of Bifrost (2.1.0.0 and below).

If you load a scene that contains a graph with a renamed or missing node, or a graph with a node that is missing an overload, warning messages will appear in the Maya Script Editor that help you to troubleshoot the issue: for example, that message may indicate that a node definition cannot be resolved or that a parameter is invalid.

The following FX graphs and nodes must be replaced by their new versions (BIFROST-5185, BIFROST-4902, BIFROST-4814, BIFROST-4776, BIFROST-4643, BIFROST-4635, BIFROST-4604):

• aero_sharpening_settings, replaced by aero_refinement_settings
• attract_repulse_influence
• get_volume_tile_info
• mask_influence
• point_scope
• read_OpenVDB, read_OpenVDB_volume
• resample_volume

Arnold Compatibility Information

To obtain the latest Arnold for Maya installer, visit the Autodesk Accounts portal.

• The minimum version of Arnold for Maya (MtoA) that supports rendering the Bifrost graph is 3.2.2.
• However, the most recent version of MtoA is recommended for the latest features, bug fixes and performance improvements. Full support of the new features of Bifrost 2.2.0.0 and higher requires version 4.1.1 or higher of MtoA.

Release Highlights

Bifrost 2.2.0.0 includes the following new features. Some of these features cause broken connections when older graphs are loaded. Please see Backward Compatibility Warnings for more information.

Escape termination (BIFROST-338, BIFROST-4104, BIFROST-4311, BIFROST-4489, BIFROST-5165)

You can now press the Esc key to stop graph computation instantly. This is useful for aborting a long simulation and lets you resume work almost immediately (although some processes may continue in the background for a short time).

To resume a simulation that has been stopped with Esc, you must move the timeline back one frame before playing back again. This works only if you have not turned off Edit > Resumable after Esc Termination to save memory.

Bifrost graph shape

Graph shapes are a major change to the integration of Bifrost into Maya. Previously there were two nodes — a graph for computation and a bif shape for viewport and offline rendering. Now there is a single node that does both. This is the new default representation of Bifrost in Maya.

The older graph nodes and associated bif shapes are still supported. To convert between them and the new graph shapes, choose Edit > Convert Graph in the Bifrost Graph Editor. Note that old graph nodes no longer appear in Maya's Outliner if Display > DAG Objects Only is on.

Easier control of multi-graph execution

You can drag and drop a graph from Maya's Outliner into a second graph in the Bifrost Graph Editor. This creates an input node that lets you use the Object and array<Object> outputs of the first graph in the second one. It is equivalent to manually connecting the output of one graph to the input of another in Maya's Node Editor.

This lets you create a chain of graphs quickly and easily, so that the first graph is not recomputed unless required. For example, you can put a heavy simulation in the first graph, and use the second graph to rapidly experiment with post-sim effects.

Fields

Fields are a new system for creating spatially varying functions without bounds or a resolution. These fields can be vector fields that represent 3D noise or flow, and used to drive simulations or deformations. They can also be scalar fields that represent things like weighting functions, shapes as signed distances, and so on.

Fields can be composed and manipulated in the graph to produce new fields. For example, you can compute gradient of a noise field, or combine fields with math operations. Field values across space can be visualized with the field_scope node.

Fields have also been integrated throughout the collection of nodes. For example:

• Volumes can be converted to fields, and fields can be sampled to create volumes.
• Fields can be used to control and modify the updated influence nodes for simulations.
• Fields can be used to drive weights and other port values for the new Scatter Pack nodes.

Improved influences for simulation (BIFROST-4643, BIFROST-4635, BIFROST-5114, and others)

Influences have been rebuilt using the new fields. As a result, you can easily edit and customize the influence compounds without modifying the simulation solvers.

In addition, the new set_influence_* compounds let you build custom influences from scratch using fields.

The performance of fields has also been improved.

Note that changes to attract_repulse_influence and mask_influence are not backwards-compatible. Graphs and compounds that use these nodes must be updated manually.

Aero improvements

Important optimizations for Aero performance (BIFROST-4720, BIFROST-4721, BIFROST-5120)

This release includes significant performance improvements for aero simulations, including better memory allocation and consumption as well as improved handling of loops.

Refining and rendering fine details in Aero simulations (BIFROST-4604, BIFROST-4413, BIFROST-4875, BIFROST-4591, BIFROST-4628)

The aero_sharpening_settings compound has been replaced by aero_refinement_settings. It features detail refinement that feeds back into the simulation. This allows dynamic refinement of fog density and temperature while still running the simulation at lower resolution. This change is not backward-compatible.

The aero_uvw_settings compound can now create any number of UVW texture coordinate sets, with control over how often they reset and how offset they are relative to each other. This node can be used to add detail to the output of the simulation in the graph or at render time. All the data required to sample the coordinates as well as their respective weights is transported with the aero object.

In addition, the new tricubic in Arnold improves the rendering of volumes, giving crisp and smooth details for aero simulations.

Physical viscosity (BIFROST-889)

The aero solver now features physical viscosity for effects like cigarette smoke and Kármán vortex streets.

Scatter Pack

The Scatter Pack is a collection of new compounds for instancing and scattering. These include high-level compounds such as:

• scatter_points, a general purpose node for scattering points onto geometry.
• create_instances, a node to turn point distributions into instances.

There are also contained mid-level nodes such as randomizers for point transformations, instance selection, orienting points to a mesh.

These nodes can all be controlled with weights, which can be driven by fields, data, properties and more. This flexibility is the result of a new graph programming concept called interpreted auto ports, which can also be added to your own compounds using some low level nodes for manipulating this data.

Volume improvements

Adaptivity-enabled volume compounds and other enhancements (BIFROST-3650, BIFROST-5073)

The new Optimized mode is available for adaptivity in the convert_to_volume,mesh_to_volume, and points_to_volume compounds. It automatically detects which areas require finer voxels and refines only in those areas while ensuring the fidelity of the overall volume. You can also control resolution manually using bounding boxes or data from properties on the input geometry.

New adaptive merge volumes compound (BIFROST-3610, BIFROST-4689)

The new merge_volumes compound offers classic Boolean operations for level sets, a multitude of combination modes for fog density, and several options to control how property data is merged. This compound also supports multi-resolution volumes as inputs, and can create an adaptive volume even if the input volumes have uniform resolution.

New field to volume compound (BIFROST-4771, BIFROST-2588)

The new field_to_volume compound converts the new fields into volumes with options for sampling as fog_density or into a level_set.

Miscellaneous volume tool enhancements (BIFROST-4785, BIFROST-4902, BIFROST-4776, BIFROST-4814)

There are several enhancements to various volume manipulation nodes including simplification for resampling volumes, rebuilding level sets, creating empty volumes, and getting volume tile info. The volume subdivision structure options for the multi-resolution tile tree are also exposed where applicable, including on the read_OpenVDB node.

Note that changes to the following nodes are not backward compatible: get_volume_tile_info, resample_volume, and read_OpenVDB.

Arnold integration improvements

The Arnold integration has seen many incremental improvements, such as only loading Bifrost once per Arnold session. Compound instances initialize faster by invoking procedurals in parallel and no longer compiling redundantly. Motion blur driven by velocity, such as in live simulations or caches of simulations, matches the scene better using improved heuristics. Arnold also supports the graph shape’s new features, such as querying a graph’s transform from inside the graph.

Cached simulations are still recommended for rendering, and you may need to select the Start On Frame motion blur setting when batch rendering live simulations.

The Arnold Alembic procedural is also now integrated with the instancing system and may be used to instantiate animated crowds of time-offset characters. Materials can be applied using Arnold Operators, particularly the MaterialX operator. Arnold Operators may also now be used with Compound instances and Render Archive instances.

Volume rendering: tricubic sampler

When rendering Bifrost volumes in Arnold, there’s a new "tricubic" sampler with better noise and performance characteristics. To use this new sampler, selectTricubic in the AiStandardVolume shader.

This new tricubic mode is 3—4× faster than the old tricubic and is only somewhat slower than trilinear. Voxel artifacts ("jaggies") are improved compared to both the old tricubic and trilinear. However, it uses more memory.

Import curves from Maya

Maya Curves can be dragged and dropped into the Bifrost graph the same way as meshes. They become strands in the graph. They may be resampled as part of the import process, either by length or by number of segments. One strands object is composed of multiple curves, so multiple curves may be dragged in to produce one strands object — you can convert this to an array of strands objects by changing the port type.

MPM improvements

Easier set-up mpm_solver_settings (BIFROST-5191, BIFROST-4575)

The mpm_solver_settings node has been slightly reorganized with new properties for quicker setup.

The new use_mesh_resolution sets the solver detail size to match the resolution of the incoming mesh (using the smallest average edge length). This prevents any grid-like artifacts from appearing during cloth simulation when the mesh resolution and solver detail size are very mismatched. This option is on by default.

When this option is on and there are cloth sources in the scene, detail_size is ignored. If there are multiple sources in the scene, the resolution derived from the cloth sources is applied to the entire MPM simulation including any sand, snow, etc., that is present. If there are no cloth sources, this option ignored.

Once the detail size is set from the cloth input mesh resolution, it can be coarsened or refined using the new detail_size_scale property. These two properties have been grouped together for usability.

MPM Cloth self-interactions and multi-solve improvements (BIFROST-5029, BIFROST-4524, BIFROST-4632, BIFROST-3937, BIFROST-4630)

MPM cloth handles self-collisions better with new methods to detect discontinuities and avoid stickiness. This improves the results for situations like a piece of cloth folding on top of itself, garments which have thin slits or any kind of discontinuity, and multiple layers of cloth on top of one another. It also improves interactions between materials like sand and snow with cloth and shells.

The new method provides improved behavior at lower resolutions where previously very fine detail size would have been required. It is controlled by the detect_discontinuity option on the mpm_solver_settings node and is enabled by default. Turn it off for faster performance if you not require the improved collisions.

Terminals (BETA)

Terminals are an alternative to output nodes for creating renderable geometry. They can be used in nested compounds, not just the top level of the graph.

Terminals have several output types: “Final” for the final renderable result, “Proxy” for a fast viewport representation, and “Diagnostic” for diagnostic viewing. By default only "Final" is rendered, but each type can be turned on and off individually. Flags on compounds with nested terminals let you toggle the outputs at any level of the graph.

Terminals are available in the public release, but they are considered to be a beta feature because a key functionality called “selective evaluation” is not yet working. This means that with default settings, Final and Proxy are both evaluated when the graph updates. Diagnostic outputs are working as intended, however.