Sending data on cange

[www2]

Hi is there a possibility that a custom protocall can send data only on change of a value than on each 1/n second.
Some thing like this:

Code: Select all

<open connection>
T0 X=0 Y=0 # data send
T1 X=0 Y=0 # no data send
T2 X=0 Y=0 # no data send
T3 X=1 Y=0 # data send
T4 X=1 Y=0 # no data send
T5 X=1 Y=0 # no data send
T6 X=1 Y=0 # no data send
T7 X=1 Y=1 # data send
T8 X=1 Y=1 # no data send
T9 X=0 Y=1 # data send
<closed connection>


[wkitty42]

which way are you talking about sending data? into FG or out of it?

i would guess that an external client should be able to determine when it sends data to FG...

[Hooray]

As far as I know, "out of the box" this is only supported by the built-in props/telnet interface, which supports the notion of "subscriptions" using listeners, which basically means that you receive notifications when a property changes that you are subscribed to.
Other than that, it'd would not exactly be difficult to implement elsewhere using pretty much the same approach.

Background at: http://wiki.flightgear.org/Telnet_usage ... nsubscribe

Technical details at:
http://wiki.flightgear.org/Improved_J661_support
http://wiki.flightgear.org/Howto:Create ... _Listeners

[www2]

@wkitty42 i look intro sending data from Flightgear to server

@Hooray that is the basic idea

For the idea i have create an protocol descriptor file that send the data if the propetries: /foobar/foo or /foobar/bar are change with a cool down period of 200 ms.

Code: Select all

<?xml version="1.0"?>
<PropertyList>
 <generic>
 
    <output>
      <line_separator>newline</line_separator>
      <var_separator>newline</var_separator>
      <binary_mode>false</binary_mode>
      <timeout>0.2</timeout> <!-- disable sending data if the last message was send in x second -->
 
      <chunk>
        <name>foo</name>
        <format>foo=%d</format>
        <node>/foobar/bar</node>
        <lisen>True</lisen> <!-- enable lisener for this object -->
      </chunk>
      <chunk>
        <name>bar</name>
        <format>bar=%d</format>
        <node>/foobar/bar</node>
        <lisen>True</lisen> <!-- enable lisener for this object -->
      </chunk>
      <chunk>
        <name>Second</name>
        <format>t=%d</format>
        <node>/sim/time/utc/second</node>
        <lisen>False</lisen> <!-- disable lisener for this object -->
      </chunk>
    </output>
 </generic>
</PropertyList>

[Hooray]

this is not directly supported as far as I can tell, so this is usually done using some kind of middleware.
Alternatively, someone familiar with the generic protocol and Nasal scripting could probably implement such a mechanism on top of generic properties, with all the update semantics implemented in scripting space.

This kind of workaround is described here: http://wiki.flightgear.org/Howto:Port_I/O_from_Nasal

[daweed]

Hello,

What i have done for FG interface is sending the data sequence (Generic Protocol using) ONLY if one property change.
I build the "data" line with each properties to send (i am using ':' to split properties)

propa:propb:propc .... etc

then compute MD5 from the "data" line, compare with the old MD5 result.
If new MD5 value is different from old one then :
=> Send data
=> Store new MD5 result to compare with on next loop

Regards

[Hooray]

Actually, it would be relatively easy to overheal the generic protocol system so that it supports SGConditions and bindings - in conjunction with headers and footers that can contain variables. Once you can express a simple state machine using the XML markup, you could also implement simple PUB/SUB mechanisms - or even call the md5sum() API or other fgcommands