Binary Parameters
Binary Parameters refers to a parameter system that VRCFaceTracking uses to send tracking data through a collection of Bool parameters that represent a float parameter.
Binary Parameters represent the value of a float parameter
in the Base-2 counting system, which is indicated by each
Binary Parameter having a Base-10 value attached
to the represented parameter. This can be thought of as the
resolution of a parameter.
In the typical use case, Binary Parameters get converted to Float Parameters within an avatar's Animation Controller via parameter driving animations or VRChat parameter type casting. This method effectively allows users to trade off tracking fidelity and parameter space of a regular float parameter.
Why use Binary Parameters on an avatar?
Binary Parameters are primarily used for reducing the amount of space a face tracking parameter consumes on an avatar.
In VRChat, avatars have a limited amount of Avatar Expression Parameter space avaliable, and using Binary Parameters can drastically reduce the footprint of a face tracking setup on an avatar with minimal impact to the perceived quality of expressions. Other platforms such as ChilloutVR can use binary parameters, but don't necessarily need to as there are no such limitations.
The caveat is that avatar setup complexity will increase quite drastically. This can lead to issues such as animation controller bugs, hard-to-debug avatar behavior, and even game crashes if not managed properly.
Use tools such as this OSCmooth fork to create stable and safe Binary Parameter conversions in VRChat.
VRCFaceTracking will dynamically detect Binary Parameters allocated on your avatar on load.
Binary Parameter Avatar Implementation
Example of a Binary Parameter compatible animation layer:
Example of a single transition from AnyState to a State (in this case: JawForward1):
Binary Parameter Representation
The following table shows how Binary Parameters work.
| Naming Scheme | Base-2 | Base-10 |
|---|---|---|
Parameter Negative | 0 0 0 0 1 | +/- |
Parameter 1 | 0 0 0 1 0 | 20 (1) |
Parameter 2 | 0 0 1 0 0 | 21 (2) |
Parameter 4 | 0 1 0 0 0 | 22 (4) |
Parameter 8 | 1 0 0 0 0 | 23 (8) |
Parameter x | x << 0 0 0 0 0 | x |
The Negative parameter represents the sign of the parameter, whether it is
positive or negative (+/-)
The value is normalized to a Float in an Animation Controller
by mapping the total Base-10 value of the Binary Parameters from <0 - (2^N)-1>,
where N is the number of Binary Parameters used, to <0.0 - 1.0>.
Effectively, each bit in the Binary Parameter set would have an effective float value
of 1/(2^N).
For example, each bit of a Binary Parameter set consisting of Parameter1, Parameter2,
and Parameter4, would be 1 / 2^3 = 1/8 = 0.125.
You might be able to notice 8 discrete steps of your eyelid openness, but maybe not 8 discrete
steps in how much your nose is sneering to the left or right!