Multiplayer Aircraft Properties

[D-ECHO]

Hi there

I'm trying to make animations over MP visible. The properties are transmitted via sim/multiplay/generic/. To use human-readable property names in the XML file, I want to use the method described in this wiki article: http://wiki.flightgear.org/Howto:Transm ... es_over_MP

Code: Select all

var rplayer = cmdarg();
# Set up property aliases for animations.
rplayer.getNode("engines/engine/prop-pos-norm", 1).alias(rplayer.getNode("sim/multiplay/generic/float[10]"));

(inside the animation .xml file, under <nasal><load>).

Unfortunately this doesn't seem to work, because engines/engine/prop-pos-norm is not existing in the multiplayer aircraft sub-tree. Am I missing something or is this a bug?

Regards and thanks

[wlbragg]

Only the obvious question, is sim/multiplay/generic/float[10] defined in the set as

Code: Select all

<multiplay>
  <chat_display>1</chat_display>
   <generic>
     ~~~
     <float n="10" alias="/engines/engine/prop-pos-norm"/>
     ~~~
   </generic>
</multiplay>

[D-ECHO]

Yes it is

[SurferTim]

I played with that yesterday, and couldn't get any nasal script to execute in nasal load.
This is from the link in your OP. Any idea what this means?

Code: Select all

##############################################################################
   # The on-load Nasal is not executed when this file is loaded as the user
   # aircraft.
   ##############################################################################

[D-ECHO]

It basically means exactly what it states - the block in <nasal> is only loaded when the aircraft is shown as a multiplayer aircraft, not when being the user aircraft

[wlbragg]

Have you tried making a filter for /engines/engine/prop-pos-norm to be a different property and trying to pass that property instead?

Where does /engines/engine/prop-pos-norm come from?

[wlbragg]

We used different property for spin in both c172p and Cub

c172p
In set.xml

Code: Select all

    <controls>
        <flight>
            <speedbrake alias="/engines/active-engine/rpm"/>
        </flight>
    </controls>

Models/

Code: Select all

    <params>
        <engine>
            <rpm>controls/flight/speedbrake</rpm>
            <crashed>sim/multiplay/generic/int[3]</crashed>
        </engine>
    </params>

J3Cub
set

Code: Select all

        <engine n="2">
            <rpm alias="/engines/active-engine/rpm"/>
        </engine>

Models/

Code: Select all

        <engine>
            <rpm>engines/engine[2]/rpm</rpm>
        </engine>

A shot in the dark, is there an initialization in the set file for /engines/engine/prop-pos-norm as in

Code: Select all

<engines>
 <engine>
  <prop-pos-norm type="float">0.0</prop-pos-norm>
 </engine>
</engines>

[D-ECHO]

The property is coming from a nasal script.

Code: Select all

         interpolate("/engines/engine/prop-pos-norm", 1.00, 5);

I have tried with a completely different property, which is not modified by anything (once declared in -set.xml) and it worked, so now I'm going to try and find out the reason it didn't work at first

Will keep you updated!

[EDIT] Yes it is initialized in the set file, it was a double but changing to a float didn't change the situation

[D-ECHO]

Turns out my mistake was that you have to purposefully look at the other model in order for it to be loaded and thus in order for the on-load nasal to be executed. Thanks everyone for the help though!

[wlbragg]

FYI

Using rplayer.initNode, may have meaning for you?

I don't know why we use the nasal initNode and then the normal MP alias property?

initNode

Code: Select all

    <nasal>
        <load>
            var rplayer = cmdarg();

            # Gear
            rplayer.initNode("sim/multiplay/generic/int[6]", 0, "BOOL");
            rplayer.initNode("sim/multiplay/generic/int[7]", 0, "BOOL");
            rplayer.initNode("sim/multiplay/generic/int[8]", 0, "BOOL");
        </load>
    </nasal>

and

Code: Select all

    <params>
        <gear_nose_broken>
            <property>sim/multiplay/generic/int[6]</property>
        </gear_nose_broken>
        <gear_left_broken>
            <property>sim/multiplay/generic/int[7]</property>
        </gear_left_broken>
        <gear_right_broken>
            <property>sim/multiplay/generic/int[8]</property>
        </gear_right_broken>
    </params>

Could this be written as

<nasal>
<load>
var rplayer = cmdarg();

rplayer.initNode("sim/multiplay/generic/int[6]", 0, "FLOAT");
or
rplayer.initNode("engines/engine/prop-pos-norm", 0, "FLOAT");

rplayer.getNode("engines/engine/prop-pos-norm", 1).alias(rplayer.getNode("sim/multiplay/generic/int[6]"));
</load>
</nasal>

[wlbragg]

OK, scratch my last post.

[MariuszXC]

Not to multiply threads I'll ask a related question here.
I want to use more compact MP data types to shorten the packet size and lessen the load on MP servers.
New/additional types are described here: https://wiki.flightgear.org/Multiplayer ... Data_types

In my -set.xml I have:

Code: Select all

      <multiplay>
         <generic>
            ...
            <float n="0" alias="/controls/flight/elevator-trim"/>
            ...
            <Short_float_norm n="0" alias="/gear/gear[0]/steering-norm"/>
            ...
         </generic>
      </multiplay>


and in my model.xml I have:

Code: Select all

   <nasal>
      <load>
         <![CDATA[
            var rplayer = cmdarg();
            ...
            rplayer.getNode("controls/flight/elevator-trim", 1).alias(rplayer.getNode("sim/multiplay/generic/float[0]") );
            ...
            rplayer.getNode("gear/gear[0]/steering-norm", 1).alias(rplayer.getNode("sim/multiplay/generic/Short_float_norm[0]") );
         ]]>
      </load>
...


This results in a Nasal error:

Code: Select all

  99.56 [ALRT]:nasal      Nasal runtime error: props.alias() with bad argument
  99.56 [ALRT]:nasal        at /opt/fg/next/install/flightgear/fgdata/Nasal/props.nas, line 43


So how do I use the new shortened data types/encodings in a correct way?

EDIT:
after looking at flightgear/src/MultiPlayer/multiplaymgr.cxx it seems that there is no direct way of requesting some data transmission types for chosen properties.
Types like short_float_norm or short_float_{1..4} are used in a fixed way for predefined properties.

Directly accessible are sim/multiplay/generic/{string[],float[],int[],short[],bool[]}.

I will need to experiment if I can repurpose transmitted but unnecessary properties gear/gear[{3,4}]/{compression,position}-norm, they use short_float_norm encoding.
Or engines/engine[1..9]/rpm in a single engine aircraft (it uses short_float_1 encoding).

[TheEagle]

I will need to experiment if I can repurpose transmitted but unnecessary properties gear/gear[{3,4}]/{compression,position}-norm, they use short_float_norm encoding.
Or engines/engine[1..9]/rpm in a single engine aircraft (it uses short_float_1 encoding).

Could you ? I'm in the process of multiplayerising my 310 so would really like to know ! And is there any possibility to monitor the outgoing MP packet size ?

[wlbragg]

Yes, you can repurpose any of those unused properties. See the c172p MP aliases in c172p-main.xml

These are a portion of what we used.

Code: Select all

    <engines>
        <!-- Following properties are part of a static list of properties
             that FlightGear transmits during multiplay. Because the number
             of properties in /sim/multiplay/generic/ is quite limited and
             the properties in /engines/ are unused, we can use them instead
             to get FlightGear to transmit all the required properties.
        -->
        <engine n="2">
            <rpm alias="/engines/active-engine/rpm"/>
        </engine>

        <!-- Amphibious front left -->
        <engine n="3">
            <n1 alias="/gear/gear[19]/compression-ft"/>
            <n2 alias="/gear/gear[19]/position-norm"/>
            <rpm alias="/gear/gear[19]/rollspeed-ms"/>
        </engine>

        <!-- Amphibious front right -->
        <engine n="4">
            <n1 alias="/gear/gear[20]/compression-ft"/>
            <n2 alias="/gear/gear[20]/position-norm"/>
            <rpm alias="/gear/gear[20]/rollspeed-ms"/>
        </engine>

        <!-- Amphibious rear left -->
        <engine n="5">
            <n1 alias="/gear/gear[21]/compression-ft"/>
            <n2 alias="/gear/gear[21]/position-norm"/>
            <rpm alias="/gear/gear[21]/rollspeed-ms"/>
        </engine>

        <!-- Amphibious rear right -->
        <engine n="6">
            <n1 alias="/gear/gear[22]/compression-ft"/>
            <n2 alias="/gear/gear[22]/position-norm"/>
            <rpm alias="/gear/gear[22]/rollspeed-ms"/>
        </engine>

        <!-- Rotation of default/26"/36" tires -->
        <engine n="7">
            <rpm alias="/gear/gear[0]/rollspeed-ms"/>
            <n1 alias="/gear/gear[1]/rollspeed-ms"/>
            <n2 alias="/gear/gear[2]/rollspeed-ms"/>
        </engine>

        <!-- Rain spray for default/26"/36" tires -->
        <engine n="8">
            <rpm alias="/gear/gear[0]/sprayspeed-ms"/>
            <n1 alias="/gear/gear[1]/sprayspeed-ms"/>
            <n2 alias="/gear/gear[2]/sprayspeed-ms"/>
        </engine>
        <engine n="9">
            <rpm alias="/gear/gear[0]/spray-density"/>
            <n1 alias="/gear/gear[1]/spray-density"/>
            <n2 alias="/gear/gear[2]/spray-density"/>
        </engine>
    </engines>

    <rotors>
        <main>
            <!-- Ski ( 23 = both nose wheels) and tiedown right -->
            <blade n="0">
                <position-deg alias="/gear/gear[23]/rollspeed-ms"/>
                <flap-deg alias="/sim/model/c172p/tiedowns/right/heading-deg"/>
            </blade>
            <blade n="1">
                <position-deg alias="/gear/gear[24]/rollspeed-ms"/>
                <flap-deg alias="/sim/model/c172p/tiedowns/right/pitch-deg"/>
            </blade>
            <blade n="2">
                <position-deg alias="/gear/gear[25]/rollspeed-ms"/>
                <flap-deg alias="/sim/model/c172p/tiedowns/right/length"/>
            </blade>

            <!-- Tiedown left -->
            <blade n="3">
                <position-deg alias="/sim/model/c172p/tiedowns/left/heading-deg"/>
                <flap-deg alias="/sim/model/c172p/tiedowns/left/pitch-deg"/>
            </blade>
            <rpm alias="/sim/model/c172p/tiedowns/left/length"/>
        </main>

        <!-- Tiedown tail -->
        <tail>
            <blade n="0">
                <position-deg alias="/sim/model/c172p/tiedowns/tail/heading-deg"/>
            </blade>
            <blade n="1">
                <position-deg alias="/sim/model/c172p/tiedowns/tail/pitch-deg"/>
            </blade>
            <rpm alias="/sim/model/c172p/tiedowns/tail/length"/>
        </tail>
    </rotors>

[MariuszXC]

Yes, I could, exactly as @wlbragg explained. However I was disgusted with how ugly a kludge it was and gave up for now. Or, to put it in a more politically-correct way, I moved it way down in my priority list for further consideration.