From 3405ea2aaac1e4be21b5d50d50cfaa72205938f1 Mon Sep 17 00:00:00 2001
From: Erik Hofman <erik@ehofman.com>
Date: Sun, 26 Jan 2020 14:10:07 +0100
Subject: [PATCH] Joystick axes can get initialized to extreme values, at least
 on Linux. Hold of working with the axis values until all values have become
 sane at least once

---
 src/Input/FGJoystickInput.cxx | 20 ++++++++++++++++++--
 src/Input/FGJoystickInput.hxx |  1 +
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/Input/FGJoystickInput.cxx b/src/Input/FGJoystickInput.cxx
index c161d449c..545e77a54 100644
--- a/src/Input/FGJoystickInput.cxx
+++ b/src/Input/FGJoystickInput.cxx
@@ -30,6 +30,8 @@
 #  include <windows.h>
 #endif
 
+#include <cmath>
+
 #include <simgear/props/props_io.hxx>
 #include "FGDeviceConfigurationMap.hxx"
 #include <Main/fg_props.hxx>
@@ -118,6 +120,7 @@ void FGJoystickInput::init()
   for (int i = 0; i < MAX_JOYSTICKS; i++) {
     jsJoystick * js = new jsJoystick(i);
     joysticks[i].plibJS.reset(js);
+    initializing[i] = true;
     
     if (js->notWorking()) {
       SG_LOG(SG_INPUT, SG_DEBUG, "Joystick " << i << " not found");
@@ -337,12 +340,25 @@ void FGJoystickInput::updateJoystick(int index, FGJoystickInput::joystick* joy,
   float delay;
   
   jsJoystick * js = joy->plibJS.get();
-  if (js == 0 || js->notWorking())
+  if (js == 0 || js->notWorking()) {
+    initializing[index] = true;
     return;
+  }
   
   js->read(&buttons, axis_values);
-  if (js->notWorking()) // If js is disconnected
+  if (js->notWorking()) { // If js is disconnected
+    initializing[index] = true;
     return;
+  }
+
+  // Joystick axes can get initialized to extreme values, at least on Linux.
+  // https://sourceforge.net/p/flightgear/codetickets/2185/
+  if (initializing[index]) {
+    for (int j = 0; j < joy->naxes; j++) {
+      if (fabsf(axis_values[j] > 0.5f)) return;
+    }
+    initializing[index] = false;
+  }
   
   // Update device status
   SGPropertyNode_ptr status = status_node->getChild("joystick", index, true);
diff --git a/src/Input/FGJoystickInput.hxx b/src/Input/FGJoystickInput.hxx
index 642950d6f..8a6f425c4 100644
--- a/src/Input/FGJoystickInput.hxx
+++ b/src/Input/FGJoystickInput.hxx
@@ -105,6 +105,7 @@ private:
       void clearAxesAndButtons();
     };
 
+    bool initializing[MAX_JOYSTICKS];
     joystick joysticks[MAX_JOYSTICKS];
     void updateJoystick(int index, joystick* joy, double dt);
 };