Fix bugs, add some docs.

Unreal/Plugins/AirSim/Source/RecordingThread.cpp

@@ -92,7 +92,7 @@ uint32 FRecordingThread::Run()
 			RenderStatus = TGraphTask<FNullGraphTask>::CreateTask(NULL).ConstructAndDispatchWhenReady(GET_STATID(STAT_FNullGraphTask_CheckRenderStatus), ENamedThreads::RenderThread);
 		}				
 
-		if (bReadPixelsStarted && !RenderStatus.GetReference() || RenderStatus->IsComplete()) {
+		if (imageColor.Num() > 0 && bReadPixelsStarted && !RenderStatus.GetReference() || RenderStatus->IsComplete()) {
 			bReadPixelsStarted = false;
 			RenderStatus = NULL;
 

docs/xbox_controller.md

@@ -0,0 +1,36 @@
+# XBox Controller
+
+To use an XBox controller with AirSim follow these steps:
+
+1. Connect XBox controller so it shows up in your PC Game Controllers:
+
+![Gamecontrollers](images/game_controllers.png)
+
+2. Connect to Pixhawk serial port using MavLinkTest.exe like this:
+````
+MavLinkTest.exe -serial:*,115200 -proxy:127.0.0.1:14550 -server:127.0.0.1:14570
+````
+
+3. Run AirSim Unreal simulator with these `~/Documents/AirSim/settings.json` settings:
+````
+    "SitlIp": "",
+    "SitlPort": 14560,
+    "UdpIp": "127.0.0.1",
+    "UdpPort": 14570,
+    "UseSerial": false,
+````
+
+4. Launch QGroundControl and you should see a new Joystick tab under stettings:
+
+![Gamecontrollers](images/qgc_joystick.png)
+
+Now calibrate the radio, and setup some handy button actions.  For example, I set mine so that 
+the 'A' button arms the drone, 'B' put it in manual flight mode, 'X' puts it in altitude hold mode
+and 'Y' puts it in position hold mode.  I also prefer the feel of the controller when I check the
+box labelled "Use exponential curve on roll,pitch, yaw" because this gives me more sensitivity for
+small movements.]
+
+QGroundControl will find your Pixhawk via the UDP proxy port 14550 setup by MavLinkTest above.
+AirSim will find your Pixhawk via the other UDP server port 14570 also setup by MavLinkTest above.
+You can also use all the QGroundControl controls for autonomous flying at this point too.
+