VARS API

The Microsoft Flight Simulator 2024 Vars API allows you to manage simulation variables using WebAssembly. This API is designed to replace the features provided by the deprecated Gauge API. The functions available for this API all listed below.

 

 

Units

Functions

Function Description
fsVarsGetUnitId Get the ID of a specific unit.

 

Types

FsUnitId

The ID of a Unit used by variables.

typedef int FsUnitId;

 

 

AVar

AVar are the Simulation Variables. They allow you to get information about - and in some case, control - various things in the simulation.

 

 

Functions

Function Description
fsVarsGetAVarId Get the ID of a specific AVar.
fsVarsAVarGet Get the value of a specific AVar.
fsVarsAVarSet Set the value of a specific AVar.
fsVarsAVarXYZGet Get the value of a specific AVar (stored as a three-dimensional vector).
fsVarsAVarXYZSet Set the value of a specific AVar (stored as a three-dimensional vector).
fsVarsAVarBufferGet Get the value of a specific AVar (stored in a buffer).
fsVarsAVarBufferSet Set the value of a specific AVar (stored in a buffer).

 

Types

FsAVarId

The ID of an AVar.

typedef int FsAVarId;

 

 

BVar

BVar are input event variables (see Input Event XML Properties for more information).

 

 

Functions

Function Description
fsVarsGetBVarId Get the ID of a specific BVar.
fsVarsBVarGet Get the value of a specific BVar.
fsVarsBVarStringGet Get the value of a specific BVar (stored as a string).
fsVarsBVarCall Call the preset associated with a specific BVar.

 

Typedef

FsBVarId

The ID of a BVar.

typedef int FsBVarId;

 

 

EVar

EVar are environment variables (see Environment Variables for more information).

 

 

Functions

Function Description
fsVarsGetEVarId Get the ID of a specific EVar.
fsVarsEVarGet Get the value of a specific EVar.

 

 

Types

FsEVarId

The ID of an EVar.

typedef int FsEVarId;

 

 

LVar

LVar are variables local to the currently running simulation. They are shared with all systems.

 

 

Functions

Function Description
fsVarsGetLVarId Get the ID of an existing LVar.
fsVarsRegisterLVar Get the ID of a specific LVar - if it exists - else create the LVar.
fsVarsGetLVarName Get the name of a specific LVar.
fsVarsLVarGet Get the value of a specific LVar.
fsVarsLVarSet Set the value of a specific LVar.

 

 

Types

FsLVarId

The ID of a LVar.

typedef int FsLVarId;

 

 

IVar

IVar are instrument variables. They are local to an instrument of a SimObject, and are accessible to all the components of the instrument's hierarchy.

 

 

Functions

Function Description

fsVarsGetIVarId

 Get the ID of an existing IVar.
fsVarsRegisterIVar Get the ID of a specific IVar - if it exists - else create the IVar.
fsVarsIVarGet Get the value of a specific IVar.
fsVarsIVarSet Set the value of a specific IVar.

 

 

Types

FsIVarId

The ID of an IVar.

typedef int FsIVarId;

 

OVar

OVar are component variables, which are variables local to a component within a simObject.

 

 

Functions

Function Description

fsVarsGetOVarId

 Get the ID of an existing OVar.
fsVarsRegisterOVar Get the ID of a specific OVar - if it exists - else create the OVar.
fsVarsOVarGet Get the value of a specific OVar.
fsVarsOVarSet Set the value of a specific OVar.

 

 

Types

FsOVarId

The ID of an OVar.

typedef int FsOVarId;

 

 

ZVar

ZVar are variables local to a SimObject. They are accessible on all instruments and components of the SimObject

NOTE: OVar can also be referenced as L:1 variables.

 

 

Functions

Function Description

fsVarsGetZVarId

 Get the ID of an existing ZVar.
fsVarsRegisterZVar Get the ID of a specific ZVar - if it exists - else create the ZVar.
fsVarsZVarGet Get the value of a specific ZVar.
fsVarsZVarSet Set the value of a specific ZVar.

 

 

Types

FsZVarId

The ID of an ZVar.

typedef int FsZVarId;

 

 

Vars Status Update

The simulation can update all the variables of a certain type - for example to reset all the values, or to remove IDs. When using some WebAssembly modules, it can be important to take this into account.

 

 

Functions

Function Description
fsVarsRegisterVarsStatusUpdateHandler Register a function to be notified when the status of a variable is changed (ie: deleted or reset).
fsVarsUnregisterVarsStatusUpdateHandler Unregister a previously registered handler with fsVarsRegisterVarsStatusUpdateHandler
fsVarsUnregisterAllVarsStatusUpdateHandler Unregister all previously registered handlers with fsVarsRegisterVarsStatusUpdateHandler

 

 

Types

eFsVarTypeFlag and FsVarTypeFlags

Flags representing one or more types of variables.

enum eFsVarTypeFlag : unsigned int
{
    FS_VAR_TYPE_AVAR = 1 << 0,
    FS_VAR_TYPE_BVAR = 1 << 1,
    FS_VAR_TYPE_EVAR = 1 << 4,
    FS_VAR_TYPE_IVAR = 1 << 8,
    FS_VAR_TYPE_LVAR = 1 << 11,
    FS_VAR_TYPE_OVAR = 1 << 14,
    FS_VAR_TYPE_ZVAR = 1 << 25,
};
typedef unsigned int FsVarTypeFlags;

 

 

FsVarUpdateOp

Enum containing the different operations that fsVarsRegisterVarsStatusUpdateHandler can receive.

enum FsVarUpdateOp : unsigned char
{
    FS_VAR_UPDATE_OP_UNKNOWN,
    FS_VAR_UPDATE_OP_REMOVE,
    FS_VAR_UPDATE_OP_RESET,
};

 

 

FsVarError

With the Vars API, a function can return an error code from the FsVarError enum:

 

Error Code Description
FS_VAR_ERROR_NONE (0) No error occurred during the function execution.
FS_VAR_ERROR_FAIL (0xFFFFFFFF) Something went wrong during the execution, but the reasons are unknown.
FS_VAR_ERROR_BAD_DATA (0x2) Arguments are correct, but the data contained within caused an error during execution.
FS_VAR_NOT_SUPPORTED (0x3) The operation is not supported with the given arguments.
FS_VAR_ERROR_INVALID_ARGS (0x4) One or more given arguments are invalid.
FS_VAR_ERROR_ALREADY_REGISTER (0x5) One or more arguments given to the register function have already been registered and must be unique.
FS_VAR_ERROR_NOT_REGISTER (0x6) The arguments given don't correspond to a registered object.

 

 

Deprecated Functions And Type Definitions

The following functions are deprecated:

 

Function Description
fsVarsGetAircraftVarId Get the ID of a specific SimVar.
fsVarsAircraftVarGet Get the value of a specific SimVar.
fsVarsAircraftVarSet Set the value of a specific SimVar.
fsVarsRegisterNamedVar Create a new NamedVar.
fsVarsGetRegisteredNamedVarId Get the ID of a named variable
fsVarsNamedVarGet Get the value of a specific NamedVar.
fsVarsNamedVarSet Set the value of a specific NamedVar.
fsVarsRegisterCustomSimVar Create a new CustomSimVar.
fsVarsCustomSimdVarGet Get the value of a specific CustomSimVar.
fsVarsCustomSimVarSet Set the value of a specific CustomSimVar.
fsVarsGetEnvironmentVarId Get the ID of an environment variable.
fsVarsEnvironmentVarGet Get the value of a specific environment variable.

 

The following type definitions are used by deprecated functions, and are therefor not useful anymore:

 

 

FsSimVarId

The ID of a SimVar.

typedef int FsSimVarId;

 

 

FsNamedVarId

The ID of a named variable (or L:Var).

typedef int FsNamedVarId;

 

 

FsCustomSimVarId

The ID of a custom SimVar. It regroups O, I and L variables.

typedef int FsCustomSimVarId;

 

 

eFsSimCustomSimVarScope

Defines the scope of a custom SimVar, where:

enum eFsSimCustomSimVarScope : unsigned char
{
    FsSimCustomSimVarScopeSim,
    FsSimCustomSimVarScopeComponent,
    FsSimCustomSimVarScopeHierarchy
};
  • FsSimCustomSimVarScopeSim: the Custom SimVar is local to the SimObject.
  • FsSimCustomSimVarScopeComponent: the Custom SimVar is local to a component.
  • FsSimCustomSimVarScopeHierarchy: the Custom SimVar is local to a component and its hierarchy.

 

FsEnvVarId

The ID of a EnvVar.

typedef int FsSimEnvId;

 

Sample

The modular WASMAircraft sample project has a preset that can be used as a reference when setting up the Vars API. You can find further details here:

 

Related Topics

  1. Programming APIs
  2. WebAssembly
  3. Debugging WebAssembly Modules