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* As an alternative, I setup a pair of "named pipes". Pipes are a unix construct, they look like a file to the program, but what you write into them is collected and held for some other application to read out. Unfortunately these are not supported in windows. Pipes are single direction, thus the need for two of them for bi-directional communication. A pipe is really simple: you open it up like any other file, and one process writes into it; the other process reads from it. In between the OS can buffer some amount of information until the reader grabs it. You can use blocking reads (carefully) to ensure FlightGear and your external FDM run in exact lockstep. | * As an alternative, I setup a pair of "named pipes". Pipes are a unix construct, they look like a file to the program, but what you write into them is collected and held for some other application to read out. Unfortunately these are not supported in windows. Pipes are single direction, thus the need for two of them for bi-directional communication. A pipe is really simple: you open it up like any other file, and one process writes into it; the other process reads from it. In between the OS can buffer some amount of information until the reader grabs it. You can use blocking reads (carefully) to ensure FlightGear and your external FDM run in exact lockstep. | ||
* Pipes imply both processes will run on the same machine, a network interface would allow the processes to live on separate machines. | * Pipes imply both processes will run on the same machine, a network interface would allow the processes to live on separate machines. | ||
* The ExternalPipe interface supports a flexible property interface, so the external FDM process can send any name/value pairs it wishes to send and the interface will dutifully copy them into the FlightGear property tree. The FDM side can also send a list of property names it would like to receive in reply and the interface will dutifully send them over the outgoing pipe every frame. This was a nice addition, and there is plenty of bandwidth through a named pipe to do this in clear text, even with a lot of extra property values. History: I used this as part of a project I did with ATC flight sim. They had their own proprietary flight dynamics applications that modeled specific aircraft in the code itself. These models had all the necessary source documentation and flight test data to satisfy FAA certification testing requirements of the final simulator. In addition, this external code modelled many of the aircraft systems for one of their high end sims. This required the ability to be flexible in what values were sent back and forth and enabled me to drive some instrument gauges directly from the external code.<ref>{{cite web | * The ExternalPipe interface supports a flexible property interface, so the external FDM process can send any name/value pairs it wishes to send and the interface will dutifully copy them into the FlightGear property tree. The FDM side can also send a list of property names it would like to receive in reply and the interface will dutifully send them over the outgoing pipe every frame. This was a nice addition, and there is plenty of bandwidth through a named pipe to do this in clear text, even with a lot of extra property values. | ||
History: I used this as part of a project I did with ATC flight sim. They had their own proprietary flight dynamics applications that modeled specific aircraft in the code itself. These models had all the necessary source documentation and flight test data to satisfy FAA certification testing requirements of the final simulator. In addition, this external code modelled many of the aircraft systems for one of their high end sims. This required the ability to be flexible in what values were sent back and forth and enabled me to drive some instrument gauges directly from the external code.<ref>{{cite web | |||
|url = https://sourceforge.net/p/flightgear/mailman/message/31900851/ | |url = https://sourceforge.net/p/flightgear/mailman/message/31900851/ | ||
|title = <nowiki> Re: [Flightgear-devel] Feeding FlightGear data through the Protocol | |title = <nowiki> Re: [Flightgear-devel] Feeding FlightGear data through the Protocol | ||