Add an example implementation for the NetFDM structure.

examples/netfdm/README

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+David Calkins writes:
+
+I've attached my sample code which works with FlightGear v0.9.3.  Perhaps this
+will be of some help to others.  I'm running FG with the launcher wizard, which
+uses the below command line options.  The sample code I attached just rolls
+back and forth ± 5 degrees so it isn't that interesting, but it works.
+
+C:\Program Files\FlightGear-0.9.3\bin\Win32\fgfs.exe
+  --fg-root=C:\Program Files\FlightGear-0.9.3\data
+  --fg-scenery=C:\Program Files\FlightGear-0.9.3\data\Scenery
+  --aircraft=c172
+  --control=joystick
+  --disable-random-objects
+  --fdm=external
+  --vc=0
+  --bpp=32
+  --timeofday=noon
+  --native-fdm=socket,in,1,,5500,udp
+
+One point of interest is the cur_time field in the FGNetFDM structure.
+I noticed that it didn't seem to matter what time I passed in.  In looking at
+the source, it appears this field is ignored completely.  So, it looks like the
+time of day would need to be determined by the command line parameters used to
+launch FlightGear.
+
+Dave 

examples/netfdm/main.cpp

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+#include <windows.h>
+#include <time.h>
+#include <iostream>
+using namespace std;
+
+#include <net_fdm.hxx>
+
+double htond (double x)	
+{
+    int * p = (int*)&x;
+    int tmp = p[0];
+    p[0] = htonl(p[1]);
+    p[1] = htonl(tmp);
+
+    return x;
+}
+
+float htonf (float x)	
+{
+    int * p = (int *)&x;
+    *p = htonl(*p);
+    return x;
+}
+
+SOCKET sendSocket = -1;
+struct sockaddr_in sendAddr;
+
+// IP and port where FG is listening
+char * fg_ip = "127.0.0.1";
+int fg_port = 5500;
+
+// update period.  controls how often updates are
+// sent to FG.  in seconds.
+int update_period = 1000;
+
+void run();
+
+int main(int argc, char ** argv)
+{
+    WSAData wd;
+    if (WSAStartup(MAKEWORD(2,0),&wd) == 0)
+    {
+        memset(&sendAddr,0,sizeof(sendAddr));
+        sendAddr.sin_family = AF_INET;
+        sendAddr.sin_port = htons(fg_port);
+        sendAddr.sin_addr.S_un.S_addr = inet_addr(fg_ip);
+
+        sendSocket = socket(AF_INET,SOCK_DGRAM,0);
+        if (sendSocket != INVALID_SOCKET)
+        {
+            run();
+        }
+        else
+        {
+            cout << "socket() failed" << endl;
+        }
+    }
+    else
+    {
+        cout << "WSAStartup() failed" << endl;
+    }
+
+    return 0;
+}
+
+#define D2R (3.14159 / 180.0)
+
+void run()
+{
+    double latitude = 45.59823; // degs
+    double longitude = -120.69202; // degs
+    double altitude = 150.0; // meters above sea level
+ 
+    float roll = 0.0; // degs
+    float pitch = 0.0; // degs
+    float yaw = 0.0; // degs
+
+    float visibility = 5000.0; // meters
+
+    while (true)
+    {
+        Sleep(update_period);
+
+        FGNetFDM fdm;
+        memset(&fdm,0,sizeof(fdm));
+        fdm.version = htonl(FG_NET_FDM_VERSION);
+
+        fdm.latitude = htond(latitude * D2R);
+        fdm.longitude = htond(longitude * D2R);
+        fdm.altitude = htond(altitude);
+
+        fdm.phi = htonf(roll * D2R);
+        fdm.theta = htonf(pitch * D2R);
+        fdm.psi = htonf(yaw * D2R);
+
+        fdm.num_engines = htonl(1);
+
+        fdm.num_tanks = htonl(1);
+        fdm.fuel_quantity[0] = htonf(100.0);
+
+        fdm.num_wheels = htonl(3);
+
+        fdm.cur_time = htonl(time(0));
+        fdm.warp = htonl(1);
+
+        fdm.visibility = htonf(visibility);
+
+        sendto(sendSocket,(char *)&fdm,sizeof(fdm),0,(struct sockaddr *)&sendAddr,sizeof(sendAddr));
+
+        static bool flag = true;
+        if (flag)
+        {
+            roll += 5.0;
+        }
+        else
+        {            
+            roll -= 5.0;
+        }
+        flag = !flag;
+    }
+}
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