[XR] Add comments, xmldoc, and conditional compilation for 2018.1

Assets/TestCameraImage.cs

 using UnityEngine.UI;
 using UnityEngine.XR.ARExtensions;
 using UnityEngine.XR.ARFoundation;
+#if !UNITY_2018_2_OR_NEWER
+using Unity.Collections;
+#endif
+/// <summary>
+/// This component tests getting the latest camera image
+/// and converting it to RGBA format. If successful,
+/// it displays the image on the screen as a RawImage
+/// and also displays information about the image.
+/// </summary>
+    /// <summary>
+    /// The UI RawImage used to display the image on screen.
+    /// </summary>
+    public RawImage rawImage
+    {
+        get { return m_RawImage; }
+        set { m_RawImage = value; }
+    }
+
+    /// <summary>
+    /// The UI Text used to display information about the image on screen.
+    /// </summary>
+    public Text imageInfo
+    {
+        get { return m_ImageInfo; }
+        set { m_ImageInfo = value; }
+    }
+
     Texture2D m_Texture;
 
     void OnEnable()
 
     unsafe void OnCameraFrameReceived(ARCameraFrameEventArgs eventArgs)
     {
+        // Attempt to get the latest camera image. If this method succeeds,
+        // it acquires a native resource that must be disposed (see below).
+        // Display some information about the camera image
+        // Choose an RGBA format.
+        // See CameraImage.FormatSupported for a complete list of supported formats.
+        var format = TextureFormat.RGBA32;
+
-            m_Texture = new Texture2D(image.width, image.height, TextureFormat.RGBA32, false);
+            m_Texture = new Texture2D(image.width, image.height, format, false);
+
+        // Convert the image to format, flipping the image across the Y axis.
+        // We can also get a sub rectangle, but we'll get the full image here.
+        var conversionParams = new CameraImageConversionParams(image, format, CameraImageTransformation.MirrorY);
-        var conversionParams = new CameraImageConversionParams(image, TextureFormat.RGBA32, CameraImageTransformation.MirrorY);
+#if UNITY_2018_2_OR_NEWER
+        // In 2018.2+, Texture2D allows us write directly to the raw texture data
+        // This allows us to do the conversion in-place without making any copies.
+#else
+        // In 2018.1, Texture2D didn't have this feature, so we'll create
+        // a temporary buffer and perform the conversion using that data.
+        int size = image.GetConvertedDataSize(conversionParams);
+        var rawTextureData = new NativeArray<byte>(size, Allocator.Temp);
+        var ptr = new IntPtr(rawTextureData.GetUnsafePtr());
+        image.Convert(conversionParams, ptr, rawTextureData.Length);
+        m_Texture.LoadRawTextureData(ptr, rawTextureData.Length);
+        rawTextureData.Dispose();
+#endif
+
+        // We must dispose of the CameraImage after we're finished
+        // with it to avoid leaking native resources.
+
+        // Apply the updated texture data to our texture
+
+        // Set the RawImage's texture so we can visualize it.
         m_RawImage.texture = m_Texture;
     }
 }