Read & Write L Vars

[ksi9302]

Hey folks!

Following my recent development of PMDG 777, 737 CDUs, I'm trying to make one for my beloved ATR and unfortunately, it doesn't have nice SDKs like the ones PMDG provides..
I believe I'll have to read and write lvars to control the CDU.
Do you think this is possible with simconnect library alone or with WASM involved?

Any ideas are welcome!

[EvenAR]

Hi! For sending keypresses, you might want to use input events (aka H-events if I'm not mistaken). This sample shows how to retrieve a list of all the available ones. Then you would use setInputEvent() to trigger them.

Annunciators/lights seem to be available as LVARs. I think you can read those in the same way as simvars now. See SimConnect_AddToDataDefinition. You can find the available LVARs in the MSFS developer menu under Tools -> Behaviors -> LocalVariables. Those starting with MSATR_MCDU1_**** are probably what you are looking for.

I'm not sure how you can extract the CDU screen text though.. Looks like LVARs are only for numeric values.

[ksi9302]

Thanks Evan, ahh, I was so naive.
I could get the setInputEvent working by doing the below.

  handle.on("inputEventsList", recvEnumerateInputEvents => {
    recvEnumerateInputEvents.inputEventDescriptors.forEach(e => {
      if (e.name == "INSTRUMENT_MCDU1_Key_CLR") {
        handle.setInputEvent(e.inputEventIdHash, 1);
        handle.setInputEvent(e.inputEventIdHash, 0);
        console.log(e.inputEventIdHash);
      }
    });
  });

However, after identifying the actual long value which was:

Long { low: -625217470, high: -1166357638, unsigned: true }

I tried constructing a variable with the exact same value using the long library.

  const clr_button = new Long(-625217470, -1166357638, true); // tried Long.fromXX methods as well..
  handle.setInputEvent(clr_button, 1);
  handle.setInputEvent(clr_button, 0);

Which sadly didn't work due to illegal value type error (not an integer or Long)
For now, I'll just store the original returned ids I need in a variable, but it would be nice to have a method to convert the value to an acceptable long type within the library..! (Or maybe there already is..?)

Thanks!

[EvenAR]

Yes, I also faced that error when I did some testing now🤔

I just published node-simconnect@4.0.0-alpha.0 which uses bigint so you don't need to deal with the Long library. Hopefully that will make things easier. bigints can easily be converted to strings and then back using for instance BigInt("12259035040569282066"). You can even use this syntax if you are using ECMAScript 2020 or newer:

handle.setInputEvent(12259035040569282066n, 1) // notice the trailing "n"

Feel free to give it a try!

[ksi9302]

SUPER,

It now works perfectly and it's almost too easy now to send any input.

To sum up the solution,

1. Reading LVARs

  handle.addToDataDefinition(
    AIRCRAFT_DATA_DEFINITION_ID,
    "L:MSATR_MCDU1_MSG_LT",
    null,
    SimConnectDataType.FLOAT64,
    0,
    SimConnectConstants.UNUSED
  );

  handle.requestDataOnSimObject(
    AIRCRAFT_DATA_REQUEST_ID,
    AIRCRAFT_DATA_DEFINITION_ID,
    SimConnectConstants.OBJECT_ID_USER,
    SimConnectPeriod.ONCE
  );

2. Writing input events

  const INSTRUMENT_MCDU1_Key_CLR = "13437276166729494594";

  // sends short click event, only sending an event with 1 will result in long click.
  handle.setInputEvent(BigInt(INSTRUMENT_MCDU1_Key_CLR), 1);
  handle.setInputEvent(BigInt(INSTRUMENT_MCDU1_Key_CLR), 0);

Much much thanks Evan!
And, Here I come ATR!

[EvenAR]

Great! I haven’t found any documentation on what the hash IDs are based on btw. I suspect that they are a result of some hashed HTML code, and that they could possibly change when the addon is updated at some point. Instead of hard coding the IDs it might be a better idea to fetch all every time your app connects and look up the IDs by the names..

[ksi9302]

Dang...! I didn't think it would change, more work..!! Thanks for the heads up mate!