Fix bug #253, at least partially

make options
--wind=nnn@mm
--visibility
--visibility-miles
--ceiling
--turbulence
work again. These options now write properties in the
/environment/config/presets
branch. The values will be applied in the property-rules
in FGDATA/Environment/interpolator.xml
Corresponds to commit e86cecf4704a4bdcf43114245d8ac94adb1f1eef
in fg/next

Environment/interpolator.xml

@@ -73,6 +73,12 @@
         <property>/environment/config/enabled</property>
       </condition>
     </enable>
+    <input>
+      <condition>
+        <property>/environment/config/presets/visibility-m-override</property>
+      </condition>
+      <property>/environment/config/presets/visibility-m</property>
+    </input>
     <input>/environment/config/interpolated/visibility-m</input>
     <output>/environment/visibility-m</output>
     <type>exponential</type>
@@ -89,6 +95,12 @@
         <property>/environment/config/enabled</property>
       </condition>
     </enable>
+    <input>
+      <condition>
+        <property>/environment/config/presets/wind-override</property>
+      </condition>
+      <property>/environment/config/presets/wind-from-north-fps</property>
+    </input>
     <input>/environment/config/interpolated/wind-from-north-fps</input>
     <output>/environment/wind-from-north-fps</output>
     <type>exponential</type>
@@ -102,6 +114,12 @@
         <property>/environment/config/enabled</property>
       </condition>
     </enable>
+    <input>
+      <condition>
+        <property>/environment/config/presets/wind-override</property>
+      </condition>
+      <property>/environment/config/presets/wind-from-east-fps</property>
+    </input>
     <input>/environment/config/interpolated/wind-from-east-fps</input>
     <output>/environment/wind-from-east-fps</output>
     <type>exponential</type>

Nasal/environment.nas

@@ -0,0 +1,45 @@
+##
+## environment.nas
+##
+##  Nasal code for implementing environment-specific functionality.
+
+##
+# Handler.  Increase visibility by one step
+#
+var increaseVisibility = func {
+	adjustVisibility(1.1);
+}
+
+##
+# Handler.  Decrease visibility by one step
+#
+var decreaseVisibility = func {
+	adjustVisibility(0.9);
+}
+
+var adjustVisibility = func( factor ) {
+    var val = visibilityProp.getValue() * factor;
+    if( val < 1.0 ) val = getprop("/environment/visibility-m");
+    if( val > 30 ) {
+        visibilityProp.setDoubleValue(val);
+	    visibilityOverrideProp.setBoolValue(1);
+        gui.popupTip(sprintf("Visibility: %.0f m", val));
+    }
+}
+
+##
+# Handler.  Reset visibility to default.
+#
+var resetVisibility = func {
+    visibilityProp.setDoubleValue(0);
+    visibilityOverrideProp.setBoolValue(0);
+}
+
+
+var visibilityProp = nil;
+var visibilityOverrideProp = nil;
+
+_setlistener("/sim/signals/nasal-dir-initialized", func {
+	visibilityProp = props.globals.initNode("/environment/config/presets/visibility-m", 0, "DOUBLE" );
+	visibilityOverrideProp = props.globals.initNode("/environment/config/presets/visibility-m-override", 0, "BOOL" );
+});

keyboard.xml

@@ -255,6 +255,15 @@ top down before the key bindings are parsed.
   </binding>
  </key>
 
+  <key n="26">
+    <name>Ctrl-Z</name>
+    <desc>Reset visibility to default</desc>
+    <binding>
+      <command>nasal</command>
+      <script>environment.resetVisibility()</script>
+    </binding>
+  </key>
+
   <key n="27">
   <name>ESC</name>
   <desc>Prompt and quit FlightGear</desc>
@@ -765,7 +774,8 @@ top down before the key bindings are parsed.
   <desc>Decrease Visibility</desc>
   <repeatable type="bool">true</repeatable>
   <binding>
-   <command>decrease-visibility</command>
+   <command>nasal</command>
+   <script>environment.decreaseVisibility()</script>
   </binding>
  </key>
 
@@ -1041,7 +1051,8 @@ top down before the key bindings are parsed.
   <desc>Increase Visibility</desc>
   <repeatable type="bool">true</repeatable>
    <binding>
-   <command>increase-visibility</command>
+   <command>nasal</command>
+   <script>environment.increaseVisibility()</script>
   </binding>
  </key>