Beacons and Strobes

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A discussion of custom beacons and strobes for authors can be found here:


	Beacon and strobe example plugin.
	This plugin overrides X-Plane's default flash patterns for the beacons and strobes.  It provides a multi-part pulse for the strobes,
	and sets the beacons to run at different rates.


#include "XPLMDataAccess.h"
#include "XPLMProcessing.h"
#include "XPLMUtilities.h"

#include <string.h>
#include <math.h>

// The time stamp that the strobes last fired.
float strobe1_t = 0.0, strobe2_t = 0.0;

/* This is the period of the entire strobe sequence. */
#define STROBE_TIME 1.0

/* This is the time between the first and second strobe firing. */
#define STROBE_OFFSET 0.2

static XPLMDataRef override_beacons_and_strobes = NULL;

// These tell us if the strobes and beacons are really on.  They take into consideration both the switch positions and electrical failures.	
static XPLMDataRef beacon_lights_on = NULL;
static XPLMDataRef strobe_lights_on = NULL;

// When we are overriding beacons and strobes, we are responsible for writing each of these per frame. 
// These are four-item arrays, so we can make multiple strobe flash patterns and separately running beacons.
static XPLMDataRef beacon_brightness_ratio = NULL;
static XPLMDataRef strobe_brightness_ratio = NULL;
// Set this to 1 if ANY strobe is on - this is what makes the clouds light up, etc.
static XPLMDataRef strobe_flash_now = NULL;

// Deferred init.  Plugins should wait until the sim is really running to do final
// initialization.  See
// for more info.
static float deferred_init(
                                   float                inElapsedSinceLastCall,    
                                   float                inElapsedTimeSinceLastFlightLoop,    
                                   int                  inCounter,    
                                   void *               inRefcon)
	strobe1_t = XPLMGetElapsedTime();
	strobe2_t = strobe1_t + STROBE_OFFSET;
	return 0;

// This is our main per-frame lighting function.  This is where we do the work X-plane would normally
// do to calculate what the beacons and strobes are doing.
static float lights_per_frame(
                                   float                inElapsedSinceLastCall,    
                                   float                inElapsedTimeSinceLastFlightLoop,    
                                   int                  inCounter,    
                                   void *               inRefcon)
	float now = XPLMGetElapsedTime();
	float beacons[4] = { 0 };
	float flash[4] = { 0 };
	int	any_flash = 0;	
	int strobes_on = XPLMGetDatai(strobe_lights_on);
	if(beacon_lights_on == NULL || strobe_lights_on == NULL || beacon_brightness_ratio == NULL)
		XPLMDebugString("We are missing our datarefs.\n");
		return 0.0f;

	// Beacon lighting calculation.  If the beacons are on, use sine and cosine for the two
	// beacons...and use a slightly different scale so they run at different spededs.

		beacons[0] = sin(now * 1.5);
		beacons[1] = cos(now);

	// Strobes.  Each time we are past our "strobe time", flash for one frame, then go out again.
	// Note that this is a TERRIBLE strobing algorithm: at high fps the strobes are on for TINY amounts of time.
	// In your strobing algorithm, make sure the strobes are on for the longer of one frame or a certain minimum time.
	// Some users do run at 80+ fps!

	if ((now - strobe1_t) > STROBE_TIME)
		flash[0] = strobes_on;
		any_flash |= strobes_on;
		strobe1_t += STROBE_TIME;
	if ((now - strobe2_t) > STROBE_TIME)
		flash[1] = strobes_on;
		any_flash |= strobes_on;
		strobe2_t += STROBE_TIME;

	XPLMSetDatai(strobe_flash_now, any_flash);

	return -1.0;	

PLUGIN_API int XPluginStart(
						char *		outName,
						char *		outSig,
						char *		outDesc)
	strcpy(outName, "Custom Beacons/Strobes Example");
	strcpy(outSig, "xplanesdk.examples.custom_beacons_strobes");
	strcpy(outDesc, "A plugin that demonstrates custom beacon/strobe patterns.");

	override_beacons_and_strobes = XPLMFindDataRef("sim/flightmodel2/lights/override_beacons_and_strobes");
	if(override_beacons_and_strobes == NULL)
		XPLMDebugString("Beacon and strobe plugin disabled - this version of x-plane doesn't support the feature.\n");
		return 0;

	beacon_lights_on = XPLMFindDataRef("sim/cockpit/electrical/beacon_lights_on");
	strobe_lights_on = XPLMFindDataRef("sim/cockpit/electrical/strobe_lights_on");
	beacon_brightness_ratio = XPLMFindDataRef("sim/flightmodel2/lights/beacon_brightness_ratio");
	strobe_brightness_ratio = XPLMFindDataRef("sim/flightmodel2/lights/strobe_brightness_ratio");
	strobe_flash_now = XPLMFindDataRef("sim/flightmodel2/lights/strobe_flash_now");	

	XPLMRegisterFlightLoopCallback(deferred_init, -1.0, NULL);
	XPLMRegisterFlightLoopCallback(lights_per_frame, -2.0, NULL);
	return 1;

PLUGIN_API void	XPluginStop(void)


PLUGIN_API void XPluginDisable(void)

PLUGIN_API int XPluginEnable(void)
	return 1;

PLUGIN_API void XPluginReceiveMessage(
					XPLMPluginID	inFromWho,
					int				inMessage,
					void *			inParam)