Camera: Documentation updates

- Clarify hardware.camera feature being only for the back camera
 - Clarify what setting a CaptureRequest field to null does
 - Use preCorrectionActiveArray instead of activeArray in list of
   possible raw output sizes
 - Clarify length of GPS processing field for camera1 API

Bug: 24540625
Bug: 23908116
Bug: 23051627
Bug: 17345901
Change-Id: Iaf11fdf626268cf30f66b3628153ec3ac770c4f4

core/java/android/hardware/Camera.java

@@ -3182,8 +3182,8 @@ public class Camera {
         }
 
         /**
-         * Sets GPS processing method. It will store up to 32 characters
-         * in JPEG EXIF header.
+         * Sets GPS processing method. The method will be stored in a UTF-8 string up to 31 bytes
+         * long, in the JPEG EXIF header.
          *
          * @param processing_method The processing method to get this location.
          */

core/java/android/hardware/camera2/CameraMetadata.java

@@ -472,13 +472,13 @@ public abstract class CameraMetadata<TKey> {
      * <li>The maximum available resolution for RAW_SENSOR streams
      *   will match either the value in
      *   {@link CameraCharacteristics#SENSOR_INFO_PIXEL_ARRAY_SIZE android.sensor.info.pixelArraySize} or
-     *   {@link CameraCharacteristics#SENSOR_INFO_ACTIVE_ARRAY_SIZE android.sensor.info.activeArraySize}.</li>
+     *   {@link CameraCharacteristics#SENSOR_INFO_PRE_CORRECTION_ACTIVE_ARRAY_SIZE android.sensor.info.preCorrectionActiveArraySize}.</li>
      * <li>All DNG-related optional metadata entries are provided
      *   by the camera device.</li>
      * </ul>
      *
-     * @see CameraCharacteristics#SENSOR_INFO_ACTIVE_ARRAY_SIZE
      * @see CameraCharacteristics#SENSOR_INFO_PIXEL_ARRAY_SIZE
+     * @see CameraCharacteristics#SENSOR_INFO_PRE_CORRECTION_ACTIVE_ARRAY_SIZE
      * @see CameraCharacteristics#REQUEST_AVAILABLE_CAPABILITIES
      */
     public static final int REQUEST_AVAILABLE_CAPABILITIES_RAW = 3;

core/java/android/hardware/camera2/CaptureRequest.java

@@ -556,6 +556,10 @@ public final class CaptureRequest extends CameraMetadata<CaptureRequest.Key<?>>
          * Set a capture request field to a value. The field definitions can be
          * found in {@link CaptureRequest}.
          *
+         * <p>Setting a field to {@code null} will remove that field from the capture request.
+         * Unless the field is optional, removing it will likely produce an error from the camera
+         * device when the request is submitted.</p>
+         *
          * @param key The metadata field to write.
          * @param value The value to set the field to, which must be of a matching
          * type to the key.

docs/html/guide/topics/manifest/uses-feature-element.jd

@@ -562,10 +562,11 @@ is sensitive to delays or lag in sound input or output.</td>
     <tr>
        <td rowspan="6">Camera</td>
        <td><code>android.hardware.camera</code></td>
-       <td>The application uses the device's camera. If the device supports
-           multiple cameras, the application uses the camera that facing
-           away from the screen.</td>
-       <td></td>
+       <td>The application uses the device's back-facing (main) camera.</td>
+       <td>Importantly, devices with only a front-facing camera will not list this
+           feature, so the <code>android.hardware.camera.any</code> feature should be
+           used instead if a camera facing any direction is acceptable for the
+           application.</td>
     </tr>
 <tr>
   <td><code>android.hardware.camera.autofocus</code></td>