XPLMProcessing API

This API allows you to get regular callbacks during the flight loop, the part of X-Plane where the plane's position calculates the physics of flight, etc. Use these APIs to accomplish periodic tasks like logging data and performing I/O.

WARNING: Do NOT use these callbacks to draw! You cannot draw during flight loop callbacks. Use the drawing callbacks (see XPLMDisplay for more info) for graphics.



You can register a flight loop callback to run either before or after the flight model is integrated by X-Plane.

xplm_FlightLoop_Phase_BeforeFlightModel0 Your callback runs before X-Plane integrates the flight model.
xplm_FlightLoop_Phase_AfterFlightModel1 Your callback runs after X-Plane integrates the flight model.


typedef void * XPLMFlightLoopID;

This is an opaque identifier for a flight loop callback. You can use this identifier to easily track and remove your callbacks, or to use the new flight loop APIs.


typedef float (* XPLMFlightLoop_f)(
                                   float                inElapsedSinceLastCall,    
                                   float                inElapsedTimeSinceLastFlightLoop,    
                                   int                  inCounter,    
                                   void *               inRefcon);    

This is your flight loop callback. Each time the flight loop is iterated through, you receive this call at the end. You receive a time since you were last called and a time since the last loop, as well as a loop counter. The 'phase' parameter is deprecated and should be ignored.

Your return value controls when you will next be called. Return 0 to stop receiving callbacks. Pass a positive number to specify how many seconds until the next callback. (You will be called at or after this time, not before.) Pass a negative number to specify how many loops must go by until you are called. For example, -1.0 means call me the very next loop. Try to run your flight loop as infrequently as is practical, and suspend it (using return value 0) when you do not need it; lots of flight loop callbacks that do nothing lowers X-Plane's frame rate.

Your callback will NOT be unregistered if you return 0; it will merely be inactive.

The reference constant you passed to your loop is passed back to you.


XPLMCreateFlightLoop_t contains the parameters to create a new flight loop callback. The strsucture can be expanded in future SDKs - always set structSize to the size of your structure in bytes.

typedef struct {
     int                       structSize;
     XPLMFlightLoopPhaseType   phase;
     XPLMFlightLoop_f          callbackFunc;
     void *                    refcon;
} XPLMCreateFlightLoop_t;


XPLM_API float                XPLMGetElapsedTime(void);

This routine returns the elapsed time since the sim started up in decimal seconds.


XPLM_API int                  XPLMGetCycleNumber(void);

This routine returns a counter starting at zero for each sim cycle computed/video frame rendered.


XPLM_API void                 XPLMRegisterFlightLoopCallback(
                                   XPLMFlightLoop_f     inFlightLoop,    
                                   float                inInterval,    
                                   void *               inRefcon);    

This routine registers your flight loop callback. Pass in a pointer to a flight loop function and a refcon. inInterval defines when you will be called. Pass in a positive number to specify seconds from registration time to the next callback. Pass in a negative number to indicate when you will be called (e.g. pass -1 to be called at the next cylcle). Pass 0 to not be called; your callback will be inactive.


XPLM_API void                 XPLMUnregisterFlightLoopCallback(
                                   XPLMFlightLoop_f     inFlightLoop,    
                                   void *               inRefcon);    

This routine unregisters your flight loop callback. Do NOT call it from your flight loop callback. Once your flight loop callback is unregistered, it will not be called again.


XPLM_API void                 XPLMSetFlightLoopCallbackInterval(
                                   XPLMFlightLoop_f     inFlightLoop,    
                                   float                inInterval,    
                                   int                  inRelativeToNow,    
                                   void *               inRefcon);    

This routine sets when a callback will be called. Do NOT call it from your callback; use the return value of the callback to change your callback interval from inside your callback.

inInterval is formatted the same way as in XPLMRegisterFlightLoopCallback; positive for seconds, negative for cycles, and 0 for deactivating the callback. If inRelativeToNow is 1, times are from the time of this call; otherwise they are from the time the callback was last called (or the time it was registered if it has never been called.


XPLM_API XPLMFlightLoopID     XPLMCreateFlightLoop(
                                   XPLMCreateFlightLoop_t * inParams);    

This routine creates a flight loop callback and returns its ID. The flight loop callback is created using the input param struct, and is inited to be unscheduled.


XPLM_API void                 XPLMDestroyFlightLoop(
                                   XPLMFlightLoopID     inFlightLoopID);    

This routine destroys a flight loop callback by ID.


XPLM_API void                 XPLMScheduleFlightLoop(
                                   XPLMFlightLoopID     inFlightLoopID,    
                                   float                inInterval,    
                                   int                  inRelativeToNow);    

This routine schedules a flight loop callback for future execution. If inInterval is negative, it is run in a certain number of frames based on the absolute value of the input. If the interval is positive, it is a duration in seconds.

If inRelativeToNow is true, ties are interpretted relative to the time this routine is called; otherwise they are relative to the last call time or the time the flight loop was registered (if never called).

THREAD SAFETY: it is legal to call this routine from any thread under the following conditions:

1. The call must be between the beginning of an XPLMEnable and the end of an XPLMDisable sequence. (That is, you must not call this routine from thread activity when your plugin was supposed to be disabled. Since plugins are only enabled while loaded, this also implies you cannot run this routine outside an XPLMStart/XPLMStop sequence.)

2. You may not call this routine re-entrantly for a single flight loop ID. (That is, you can't enable from multiple threads at the same time.)

3. You must call this routine between the time after XPLMCreateFlightLoop returns a value and the time you call XPLMDestroyFlightLoop. (That is, you must ensure that your threaded activity is within the life of the object. The SDK does not check this for you, nor does it synchronize destruction of the object.)

4. The object must be unscheduled if this routine is to be called from a thread other than the main thread.