UDP protocol support added

ExtPlane.pro

@@ -15,4 +15,4 @@ defined(XPLANE_SDK_PATH, var) {
     warning("No X-Plane SDK found in ../XPlaneSDK or ~/SDK - not building X-Plane plugin")
 }
 
-OTHER_FILES += README.md clients/extplane-client-qt/README Dockerfile scripts/*
+OTHER_FILES += README.md UDP.md clients/extplane-client-qt/README Dockerfile scripts/*

README.md

@@ -23,6 +23,7 @@ This will eventually be fixed.
 * Simulate key and button presses
 * Execute commands
 * Load situations
+* High-performance UDP option
 * Free & open source under GPLv3
 * Client libraries available for Qt (c++), Java and C#
 
@@ -249,6 +250,13 @@ sub sim/flightmodel/engine/ENGN_thro
 WRONG: sub sim/flightmodel/engine/ENGN_thro[1]
 ```
 
+### High-performance UDP output ###
+
+ExtPlane supports tight UDP protocol for basic dataref types (int, float, double)
+from simulator to client. Add modifier udp to ref name to request it in UDP.
+UDP datarefs are sent every flight loop using lightweight protocol.
+
+See [this file](UDP.md) for details.
 
 ### Keys and Buttons ###
 
@@ -286,12 +294,11 @@ Command identifiers are strings that look like datarefs.
 Supported settings are:
 * **update_interval {value}**          How often ExtPlane should update its data from X-Plane, in seconds. Use as high value as possible here for best performance. For example 0.16 would mean 60Hz, 0.33 = 30Hz, 0.1 = 10Hz etc.. Must be a positive float. Default is 0.33.
 
-
-
 ## Protocol Output ##
 
 * **EXTPLANE {protocol}**              Sent when connected. Protocol is currently 1.
 * **EXTPLANE-VERSION {version}**       Sent when connected. Feature version integer, which is incremented with each new bug fix or feature.
+* **CLIENT-ID {clientid}**             Client ID used with UDP protocol
 * **EXTPLANE-WARNING {message}**       Show warning message for developer and/or user
 * **u{type} {dataref} {value}**        Dataref has changed in value based on accuracy.
     * Types may be `i` (int), `f` (float), `d` (double), `ia` (int array), `fa` (float array), or `b` (data).

UDP.md

@@ -0,0 +1,75 @@
+# ExtPlane UDP protocol #
+
+So you want to get frame-perfect datarefs with high performance?
+You are reading the right file.
+
+Note that currently you can only subscribe (not write) dataref.
+Datarefs are limited to only basic types (int, float, double).
+Arrays or other more complex values are not supported via UDP.
+
+Writing via UDP might be implemented some day.. PR welcome.
+
+## Get the client ID ##
+
+When connected to ExtPlane, store the number after CLIENT-ID.
+That is your unique client ID used by UDP.
+
+## Listen to UDP
+
+Bind to UDP port 52000 + client_id
+
+Different ports make it easy to run multiple clients on same machine
+and reduce error probability.
+
+## Subscribe to datarefs
+
+Add modifier udp to dataref name. Do not set accuracy, UDP datarefs are sent
+every flight loop. For example:
+
+```
+sub sim/flightmodel/misc/h_ind:udp
+```
+
+ExtPlane will reply with "udp", ref_id, ref type, and ref name.
+
+Example:
+
+```
+udp 42 f sim/flightmodel/misc/h_ind:udp
+```
+
+Store the ref_id value, you'll need it later. You also need to know
+the datatype of the ref - in this case f = float. Ref_id is
+unsigned int 16 bits.
+
+ExtPlane will now send this ref in UDP packet every flight loop (usually
+60hz).
+
+## UDP Datagram content ##
+
+Here is the spec for the data content and size in bytes for each part.
+
+"EXTP_" (5) - header string
+client_id (1, uint8) - client id, should be same as CLIENT-ID sent earlier
+int_count (2, uint16) - number of integer values to read
+
+Repeated int_count times:
+
+ref_id (2, uint16) - ref id, same you got when subscribing
+value  (4, int32) - value of the int dataref
+
+"Ef" (2) - header for float data
+float_count (2, uint16) - number of float values to read
+
+Repeated float_count times:
+
+ref_id (2, uint16) - ref id
+value  (4, float) - value of the float dataref
+
+"Ed" (2) - header for double data
+double_count (2, uint16) - number of double values to read
+
+Repeated float_count times:
+
+ref_id (2, uint16) - ref id
+value  (8, double) - value of the double dataref