WIP: Field type inferencing using a constraint solver method #120420

Lukas Tönne · 2024-04-09T11:29:28+02:00

Lukas Tönne commented

2024-04-09 11:29:28 +02:00

Refactoring of the field type inferencing mechanism for node trees using a general-purpose constraint solver.

Field types can be described as a set of discrete states (single value or fields), with constraints between them (which socket connections are valid). The job of the inferencing mechanism is to determine possible states for each internal socket, as well as produce the FieldInferencingInterface for the tree as a whole.

The legacy algorithm resolves this using left-to-right and right-to-left passes based on topological node sorting. This works reasonably well, but gets complicated by recent addition of loop zones and planned features such

Grid socket types
List sockets
Data type inferencing ("rainbow" sockets)

The addition of zones broke the simple topological dependencies between nodes and requires repetition of the entire solver to ensure all constraints are satisfied. Even before that there were small solver loops nested inside the broad topological passes. The implementation also mixes socket state and constraint properties (always_single, is_field_source). Taken together this results in a complicated system that is hard to understand and quite verbose.

This refactoring adds a general-purpose solver for constraint satisfaction problems (CSP) in BLI. This solver is agnostic to the specific field type inference problem (see the unit tests for some examples of general use). This solver is based on the AC3 algorithm, which is a common method of solving such discrete constraint systems. It is well suited to the problem at hand due to the small domain size.

The legacy solver is moved into a separate file. It is still used when the experimental feature is disabled, and also serves as "ground truth" for verifying the result of the new solver.

Refactoring of the field type inferencing mechanism for node trees using a general-purpose constraint solver. Field types can be described as a set of discrete states (single value or fields), with _constraints_ between them (which socket connections are valid). The job of the inferencing mechanism is to determine possible states for each internal socket, as well as produce the `FieldInferencingInterface` for the tree as a whole. The legacy algorithm resolves this using left-to-right and right-to-left passes based on topological node sorting. This works reasonably well, but gets complicated by recent addition of loop zones and planned features such - Grid socket types - List sockets - Data type inferencing ("rainbow" sockets) The addition of zones broke the simple topological dependencies between nodes and requires repetition of the entire solver to ensure all constraints are satisfied. Even before that there were small solver loops nested inside the broad topological passes. The implementation also mixes socket _state_ and _constraint properties_ (`always_single`, `is_field_source`). Taken together this results in a complicated system that is hard to understand and quite verbose. This refactoring adds a general-purpose solver for _constraint satisfaction problems_ ([CSP](https://en.wikipedia.org/wiki/Constraint_satisfaction_problem)) in BLI. This solver is agnostic to the specific field type inference problem (see the [unit tests](https://projects.blender.org/LukasTonne/blender/src/branch/socket-type-inference/source/blender/blenlib/tests/BLI_constraint_satisfaction_test.cc) for some examples of general use). This solver is based on the [AC3 algorithm](https://en.wikipedia.org/wiki/AC-3_algorithm), which is a common method of solving such discrete constraint systems. It is well suited to the problem at hand due to the small domain size. The legacy solver is moved into a separate file. It is still used when the experimental feature is disabled, and also serves as "ground truth" for verifying the result of the new solver.

❤️ 4 🚀 1

Lukas Tönne added 47 commits 2024-04-09 11:29:43 +02:00

7ac85ef397 Initial implementation of the AC3 algorithm for resolving socket types.

b1be9e94fc More debug printiiiing.

d4048cf06b Nicer printing.

3211ba1309 Fixed binary constraint resolution.

dbcb3a51b7 Initial steps for field inference with new solver.

52d7ffcd70 Merge branch 'main' into socket-type-inference

23c03502fa More constraints for field inference.

945bb8ce12 new interface.

f6cc0d9a88 Merge branch 'main' into socket-type-inference

243e400c07 Use interface variables for the group input/output nodes.

56df2b0245 Merge branch 'main' into socket-type-inference

8c976aa345 Fixed ranges for interface sockets.

483b14da79 Cleanup: more specialized logging functions.

0e2be8a6e7 set_variable_names logger function.

8f71366ba7 Merge branch 'main' into socket-type-inference

a5d83bfdf1 More logging functions.

aef69e3f98 progress

1fcf9240a4 Operator to explicitly dump debug data into a json file.

948b6a9c08 Skip unavailable sockets for constraints.

f0c3d9c556 stuff

dcc2d51acd Merge branch 'main' into socket-type-inference

0e1e2a9514 Merge branch 'main' into socket-type-inference

fbcfd48d2a Replace int variable indexes with formalized (Mutable)VariableKey.

This helps ensure correctness and clarifies which of the variables is
being modified.

f662508fe1 Merge branch 'main' into socket-type-inference

c2552b0dcd Moved constraint satisfaction to a new BLI file.

74b92bae90 Added new BLI test for constraint satisfaction.

f52223d789 Reverted the VariableRef struct in favor of a simpler VariableIndex alias.

64265f4ae0 Fix build errors.

4dee63d459 Fix incorrect dependency scheduling that caused infinte loops.

366ef46858 Finished the basic existing test.

fd27c22dac Build support for (anti)symmetric constraints into the ConstraintSet.

1291d4a41e Added tests for over- and under-constrained systems.

b3744a2ebc Added a Sudoku solver test, because why not.

02613546ca Added an experimental flag to toggle new field inferencing algorithm.

17298bb464 Added a verification step that optionally compares old and new inferencing.

d48be0ad97 Add verification for the overall tree interface as well.

610cd372e9 Avoid checking conditions twice.

1f482030c1 Check for empty domain errors to cover all potential cases in verification.

67a45c00f7 Added utility struct for consistent socket variables and fix current errors.

410ecc34cd Better error messages.

a703e66d97 Use the symmetric constraint declaration for zone relationships.

76e265eba1 Update the socket shapes after solving constraints.

e129d1b99c Add link constraints in the output->input direction.

This forces inputs to become fields when connected outputs can only be
fields (field sources).

There are still missing internal constraints that unify field types
within a single node.

8232759635 Add constraints for internal dependencies to propagate fields from inputs to outputs.

b3128a83e7 Use the gather function to determine group interface.

The states of internal nodes include superpositions of single value and
field to indicate that a socket _can_ be either, but the overall group
interface should only include the concrete connected types. A single
value socket connected to a group output creates a single-or-field
socket, while the group interface should consider it a single value.
The `find_group_output_dependencies` has to be used to determine the
interface types for the tree as a whole, rather than the state of
internal sockets.

a09bce3251 Merge branch 'main' into socket-type-inference

daf213706d Moved legacy propagation code into its own file for easy comparison.

Lukas Tönne added this to the Nodes & Physics project 2024-04-09 11:29:46 +02:00

Lukas Tönne added 1 commit 2024-04-19 14:56:18 +02:00

c71dd02032 Merge branch 'main' into socket-type-inference

Lukas Tönne added 2 commits 2024-04-21 08:45:48 +02:00

415b24c3e1 Merge branch 'main' into socket-type-inference

10a6d84ace Merge branch 'socket-type-inference' of projects.blender.org:LukasTonne/blender into socket-type-inference

Lukas Tönne added 1 commit 2024-04-28 11:16:42 +02:00

1a154dbae2 Merge branch 'main' into socket-type-inference

This pull request has changes conflicting with the target branch.