content: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.hardware.camera2;
  
  import android.annotation.CallbackExecutor;
  import android.annotation.NonNull;
  import android.annotation.Nullable;
  import android.hardware.camera2.params.OutputConfiguration;
  import android.os.Handler;
  import android.view.Surface;
  
  import java.util.List;
  import java.util.concurrent.Executor;
  
  /**
   * A configured capture session for a {@link CameraDevice}, used for capturing images from the
   * camera or reprocessing images captured from the camera in the same session previously.
   *
   * <p>A CameraCaptureSession is created by providing a set of target output surfaces to
   * {@link CameraDevice#createCaptureSession createCaptureSession}, or by providing an
   * {@link android.hardware.camera2.params.InputConfiguration} and a set of target output surfaces to
   * {@link CameraDevice#createReprocessableCaptureSession createReprocessableCaptureSession} for a
   * reprocessable capture session. Once created, the session is active until a new session is
   * created by the camera device, or the camera device is closed.</p>
   *
   * <p>All capture sessions can be used for capturing images from the camera but only reprocessable
   * capture sessions can reprocess images captured from the camera in the same session previously.
   * </p>
   *
   * <p>Creating a session is an expensive operation and can take several hundred milliseconds, since
   * it requires configuring the camera device's internal pipelines and allocating memory buffers for
   * sending images to the desired targets. Therefore the setup is done asynchronously, and
   * {@link CameraDevice#createCaptureSession createCaptureSession} and
   * {@link CameraDevice#createReprocessableCaptureSession createReprocessableCaptureSession} will
   * send the ready-to-use CameraCaptureSession to the provided listener's
   * {@link CameraCaptureSession.StateCallback#onConfigured onConfigured} callback. If configuration
   * cannot be completed, then the
   * {@link CameraCaptureSession.StateCallback#onConfigureFailed onConfigureFailed} is called, and the
   * session will not become active.</p>
   *<!--
   * <p>Any capture requests (repeating or non-repeating) submitted before the session is ready will
   * be queued up and will begin capture once the session becomes ready. In case the session cannot be
   * configured and {@link StateCallback#onConfigureFailed onConfigureFailed} is called, all queued
   * capture requests are discarded.</p>
   *-->
   * <p>If a new session is created by the camera device, then the previous session is closed, and its
   * associated {@link StateCallback#onClosed onClosed} callback will be invoked.  All
   * of the session methods will throw an IllegalStateException if called once the session is
   * closed.</p>
   *
   * <p>A closed session clears any repeating requests (as if {@link #stopRepeating} had been called),
   * but will still complete all of its in-progress capture requests as normal, before a newly
   * created session takes over and reconfigures the camera device.</p>
   */
  public abstract class CameraCaptureSession implements AutoCloseable {
  
      /**
       * Used to identify invalid session ID.
       * @hide
       */
      public static final int SESSION_ID_NONE = -1;
  
      /**
       * Get the camera device that this session is created for.
       */
      @NonNull
      public abstract CameraDevice getDevice();
  
      /**
       * <p>Pre-allocate all buffers for an output Surface.</p>
       *
       * <p>Normally, the image buffers for a given output Surface are allocated on-demand,
       * to minimize startup latency and memory overhead.</p>
       *
       * <p>However, in some cases, it may be desirable for the buffers to be allocated before
       * any requests targeting the Surface are actually submitted to the device. Large buffers
       * may take some time to allocate, which can result in delays in submitting requests until
       * sufficient buffers are allocated to reach steady-state behavior. Such delays can cause
       * bursts to take longer than desired, or cause skips or stutters in preview output.</p>
       *
       * <p>The prepare() method can be used to perform this preallocation. It may only be called for
       * a given output Surface before that Surface is used as a target for a request. The number of
       * buffers allocated is the sum of the count needed by the consumer providing the output
       * Surface, and the maximum number needed by the camera device to fill its pipeline. Since this
       * may be a larger number than what is actually required for steady-state operation, using
       * prepare may result in higher memory consumption than the normal on-demand behavior results
       * in. Prepare() will also delay the time to first output to a given Surface, in exchange for
       * smoother frame rate once the allocation is complete.</p>
       *
       * <p>For example, an application that creates an
       * {@link android.media.ImageReader#newInstance ImageReader} with a maxImages argument of 10,
       * but only uses 3 simultaneous Images at once would normally only cause those 3 images to be
       * allocated (plus what is needed by the camera device for smooth operation).  But using
       * prepare() on the ImageReader Surface will result in all 10 Images being allocated. So
       * applications using this method should take care to request only the number of buffers
       * actually necessary for their application.</p>
       *
       * <p>If the same output Surface is used in consecutive sessions (without closing the first
       * session explicitly), then its already-allocated buffers are carried over, and if it was
       * used as a target of a capture request in the first session, prepare cannot be called on it
       * in the second session.</p>
       *
       * <p>Once allocation is complete, {@link StateCallback#onSurfacePrepared} will be invoked with
       * the Surface provided to this method. Between the prepare call and the onSurfacePrepared call,
       * the Surface provided to prepare must not be used as a target of a CaptureRequest submitted
       * to this session.</p>
       *
       * <p>Note that if 2 surfaces share the same stream via {@link
       * OutputConfiguration#enableSurfaceSharing} and {@link OutputConfiguration#addSurface},
       * prepare() only needs to be called on one surface, and {link
       * StateCallback#onSurfacePrepared} will be triggered for both surfaces.</p>
       *
       * <p>{@link android.hardware.camera2.CameraCharacteristics#INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY LEGACY}
       * devices cannot pre-allocate output buffers; for those devices,
       * {@link StateCallback#onSurfacePrepared} will be immediately called, and no preallocation is
       * done.</p>
       *
       * @param surface the output Surface for which buffers should be pre-allocated. Must be one of
       * the output Surfaces used to create this session.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException if the Surface is invalid, not part of this Session, or has
       *                                  already been used as a target of a CaptureRequest in this
       *                                  session or immediately prior sessions.
       *
       * @see StateCallback#onSurfacePrepared
       */
      public abstract void prepare(@NonNull Surface surface) throws CameraAccessException;
  
      /**
       * <p>Pre-allocate at most maxCount buffers for an output Surface.</p>
       *
       * <p>Like the {@link #prepare(Surface)} method, this method can be used to allocate output
       * buffers for a given Surface.  However, while the {@link #prepare(Surface)} method allocates
       * the maximum possible buffer count, this method allocates at most maxCount buffers.</p>
       *
       * <p>If maxCount is greater than the possible maximum count (which is the sum of the buffer
       * count requested by the creator of the Surface and the count requested by the camera device),
       * only the possible maximum count is allocated, in which case the function acts exactly like
       * {@link #prepare(Surface)}.</p>
       *
       * <p>The restrictions on when this method can be called are the same as for
       * {@link #prepare(Surface)}.</p>
       *
       * <p>Repeated calls to this method are allowed, and a mix of {@link #prepare(Surface)} and
       * this method is also allowed. Note that after the first call to {@link #prepare(Surface)},
       * subsequent calls to either prepare method are effectively no-ops.  In addition, this method
       * is not additive in terms of buffer count.  This means calling it twice with maxCount = 2
       * will only allocate 2 buffers, not 4 (assuming the possible maximum is at least 2); to
       * allocate two buffers on the first call and two on the second, the application needs to call
       * prepare with prepare(surface, 2) and prepare(surface, 4).</p>
       *
       * @param maxCount the buffer count to try to allocate. If this is greater than the possible
       *                 maximum for this output, the possible maximum is allocated instead. If
       *                 maxCount buffers are already allocated, then prepare will do nothing.
       * @param surface the output Surface for which buffers should be pre-allocated.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error.
       * @throws IllegalStateException if this session is no longer active, either because the
       *                               session was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException if the Surface is invalid, not part of this Session,
       *                                  or has already been used as a target of a CaptureRequest in
       *                                  this session or immediately prior sessions without an
       *                                  intervening tearDown call.
       *
       * @hide
       */
      public abstract void prepare(int maxCount, @NonNull Surface surface)
              throws CameraAccessException;
  
      /**
       * <p>Free all buffers allocated for an output Surface.</p>
       *
       * <p>Normally, once allocated, the image buffers for a given output Surface remain allocated
       * for the lifetime of the capture session, to minimize latency of captures and to reduce
       * memory allocation overhead.</p>
       *
       * <p>However, in some cases, it may be desirable for allocated buffers to be freed to reduce
       * the application's memory consumption, if the particular output Surface will not be used by
       * the application for some time.</p>
       *
       * <p>The tearDown() method can be used to perform this operation. After the call finishes, all
       * unfilled image buffers will have been freed. Any future use of the target Surface may require
       * allocation of additional buffers, as if the session had just been created.  Buffers being
       * held by the application (either explicitly as Image objects from ImageReader, or implicitly
       * as the current texture in a SurfaceTexture or the current contents of a RS Allocation, will
       * remain valid and allocated even when tearDown is invoked.</p>
       *
       * <p>A Surface that has had tearDown() called on it is eligible to have prepare() invoked on it
       * again even if it was used as a request target before the tearDown() call, as long as it
       * doesn't get used as a target of a request between the tearDown() and prepare() calls.</p>
       *
       * @param surface the output Surface for which buffers should be freed. Must be one of the
       * the output Surfaces used to create this session.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error.
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException if the Surface is invalid, not part of this Session, or has
       *                                  already been used as a target of a CaptureRequest in this
       *                                  session or immediately prior sessions.
       *
       * @hide
       */
      public abstract void tearDown(@NonNull Surface surface) throws CameraAccessException;
  
      /**
       * <p>Finalize the output configurations that now have their deferred and/or extra Surfaces
       * included.</p>
       *
       * <p>For camera use cases where a preview and other output configurations need to be
       * configured, it can take some time for the preview Surface to be ready. For example, if the
       * preview Surface is obtained from {@link android.view.SurfaceView}, the SurfaceView will only
       * be ready after the UI layout is done, potentially delaying camera startup.</p>
       *
       * <p>To speed up camera startup time, the application can configure the
       * {@link CameraCaptureSession} with the eventual preview size (via
       * {@link OutputConfiguration#OutputConfiguration(Size,Class) a deferred OutputConfiguration}),
       * and defer the preview output configuration until the Surface is ready. After the
       * {@link CameraCaptureSession} is created successfully with this deferred output and other
       * normal outputs, the application can start submitting requests as long as they do not include
       * deferred output Surfaces. Once a deferred Surface is ready, the application can add the
       * Surface to the deferred output configuration with the
       * {@link OutputConfiguration#addSurface} method, and then update the deferred output
       * configuration via this method, before it can submit capture requests with this output
       * target.</p>
       *
       * <p>This function can also be called in case where multiple surfaces share the same
       * OutputConfiguration, and one of the surfaces becomes available after the {@link
       * CameraCaptureSession} is created. In that case, the application must first create the
       * OutputConfiguration with the available Surface, then enable further surface sharing via
       * {@link OutputConfiguration#enableSurfaceSharing}, before creating the CameraCaptureSession.
       * After the CameraCaptureSession is created, and once the extra Surface becomes available, the
       * application must then call {@link OutputConfiguration#addSurface} before finalizing the
       * configuration with this method.</p>
       *
       * <p>If the provided OutputConfigurations are unchanged from session creation, this function
       * call has no effect. This function must only be called once for a particular output
       * configuration. </p>
       *
       * <p>The output Surfaces included by this list of
       * {@link OutputConfiguration OutputConfigurations} can be used as {@link CaptureRequest}
       * targets as soon as this call returns.</p>
       *
       * <p>This method is not supported by
       * {@link CameraCharacteristics#INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY LEGACY}-level devices.</p>
       *
       * @param outputConfigs a list of {@link OutputConfiguration OutputConfigurations} that
       *            have had {@link OutputConfiguration#addSurface addSurface} invoked with a valid
       *            output Surface after {@link CameraDevice#createCaptureSessionByOutputConfigurations}.
       * @throws CameraAccessException if the camera device is no longer connected or has encountered
       *             a fatal error.
       * @throws IllegalStateException if this session is no longer active, either because the session
       *             was explicitly closed, a new session has been created, or the camera device has
       *             been closed.
       * @throws IllegalArgumentException for invalid output configurations, including ones where the
       *             source of the Surface is no longer valid or the Surface is from a unsupported
       *             source. Or if one of the output configuration was already finished with an
       *             included surface in a prior call.
       */
      public abstract void finalizeOutputConfigurations(
              List<OutputConfiguration> outputConfigs) throws CameraAccessException;
  
      /**
       * <p>Submit a request for an image to be captured by the camera device.</p>
       *
       * <p>The request defines all the parameters for capturing the single image,
       * including sensor, lens, flash, and post-processing settings.</p>
       *
       * <p>Each request will produce one {@link CaptureResult} and produce new frames for one or more
       * target Surfaces, set with the CaptureRequest builder's
       * {@link CaptureRequest.Builder#addTarget} method. The target surfaces (set with
       * {@link CaptureRequest.Builder#addTarget}) must be a subset of the surfaces provided when this
       * capture session was created.</p>
       *
       * <p>Multiple regular and reprocess requests can be in progress at once. If there are only
       * regular requests or reprocess requests in progress, they are processed in first-in,
       * first-out order. If there are both regular and reprocess requests in progress, regular
       * requests are processed in first-in, first-out order and reprocess requests are processed in
       * first-in, first-out order, respectively. However, the processing order of a regular request
       * and a reprocess request in progress is not specified. In other words, a regular request
       * will always be processed before regular requets that are submitted later. A reprocess request
       * will always be processed before reprocess requests that are submitted later. However, a
       * regular request may not be processed before reprocess requests that are submitted later.<p>
       *
       * <p>Requests submitted through this method have higher priority than
       * those submitted through {@link #setRepeatingRequest} or
       * {@link #setRepeatingBurst}, and will be processed as soon as the current
       * repeat/repeatBurst processing completes.</p>
       *
       * <p>All capture sessions can be used for capturing images from the camera but only capture
       * sessions created by
       * {@link CameraDevice#createReprocessableCaptureSession createReprocessableCaptureSession}
       * can submit reprocess capture requests. Submitting a reprocess request to a regular capture
       * session will result in an {@link IllegalArgumentException}.</p>
       *
       * @param request the settings for this capture
       * @param listener The callback object to notify once this request has been
       * processed. If null, no metadata will be produced for this capture,
       * although image data will still be produced.
       * @param handler the handler on which the listener should be invoked, or
       * {@code null} to use the current thread's {@link android.os.Looper
       * looper}.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException if the request targets no Surfaces or Surfaces that are not
       *                                  configured as outputs for this session; or the request
       *                                  targets a set of Surfaces that cannot be submitted
       *                                  simultaneously in a reprocessable capture session; or a
       *                                  reprocess capture request is submitted in a
       *                                  non-reprocessable capture session; or the reprocess capture
       *                                  request was created with a {@link TotalCaptureResult} from
       *                                  a different session; or the capture targets a Surface in
       *                                  the middle of being {@link #prepare prepared}; or the
       *                                  handler is null, the listener is not null, and the calling
       *                                  thread has no looper.
       *
       * @see #captureBurst
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see #abortCaptures
       * @see CameraDevice#createReprocessableCaptureSession
       */
      public abstract int capture(@NonNull CaptureRequest request,
              @Nullable CaptureCallback listener, @Nullable Handler handler)
              throws CameraAccessException;
  
      /**
       * <p>Submit a request for an image to be captured by the camera device.</p>
       *
       * <p>The behavior of this method matches that of
       * {@link #capture(CaptureRequest, CaptureCallback, Handler)},
       * except that it uses {@link java.util.concurrent.Executor} as an argument
       * instead of {@link android.os.Handler}.</p>
       *
       * @param request the settings for this capture
       * @param executor the executor which will be used for invoking the listener.
       * @param listener The callback object to notify once this request has been
       * processed.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException if the request targets no Surfaces or Surfaces that are not
       *                                  configured as outputs for this session; or the request
       *                                  targets a set of Surfaces that cannot be submitted
       *                                  simultaneously in a reprocessable capture session; or a
       *                                  reprocess capture request is submitted in a
       *                                  non-reprocessable capture session; or the reprocess capture
       *                                  request was created with a {@link TotalCaptureResult} from
       *                                  a different session; or the capture targets a Surface in
       *                                  the middle of being {@link #prepare prepared}; or the
       *                                  executor is null, or the listener is not null.
       *
       * @see #captureBurst
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see #abortCaptures
       * @see CameraDevice#createReprocessableCaptureSession
       */
      public int captureSingleRequest(@NonNull CaptureRequest request,
              @NonNull @CallbackExecutor Executor executor, @NonNull CaptureCallback listener)
              throws CameraAccessException {
          throw new UnsupportedOperationException("Subclasses must override this method");
      }
  
      /**
       * Submit a list of requests to be captured in sequence as a burst. The
       * burst will be captured in the minimum amount of time possible, and will
       * not be interleaved with requests submitted by other capture or repeat
       * calls.
       *
       * <p>Regular and reprocess requests can be mixed together in a single burst. Regular requests
       * will be captured in order and reprocess requests will be processed in order, respectively.
       * However, the processing order between a regular request and a reprocess request is not
       * specified. Each capture produces one {@link CaptureResult} and image buffers for one or more
       * target {@link android.view.Surface surfaces}. The target surfaces (set with
       * {@link CaptureRequest.Builder#addTarget}) must be a subset of the surfaces provided when
       * this capture session was created.</p>
       *
       * <p>The main difference between this method and simply calling
       * {@link #capture} repeatedly is that this method guarantees that no
       * other requests will be interspersed with the burst.</p>
       *
       * <p>All capture sessions can be used for capturing images from the camera but only capture
       * sessions created by
       * {@link CameraDevice#createReprocessableCaptureSession createReprocessableCaptureSession}
       * can submit reprocess capture requests. Submitting a reprocess request to a regular
       * capture session will result in an {@link IllegalArgumentException}.</p>
       *
       * @param requests the list of settings for this burst capture
       * @param listener The callback object to notify each time one of the
       * requests in the burst has been processed. If null, no metadata will be
       * produced for any requests in this burst, although image data will still
       * be produced.
       * @param handler the handler on which the listener should be invoked, or
       * {@code null} to use the current thread's {@link android.os.Looper
       * looper}.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the requests target no Surfaces, or the requests target
       *                                  Surfaces not currently configured as outputs; or one of the
       *                                  requests targets a set of Surfaces that cannot be submitted
       *                                  simultaneously in a reprocessable capture session; or a
       *                                  reprocess capture request is submitted in a
       *                                  non-reprocessable capture session; or one of the reprocess
       *                                  capture requests was created with a
       *                                  {@link TotalCaptureResult} from a different session; or one
       *                                  of the captures targets a Surface in the middle of being
       *                                  {@link #prepare prepared}; or if the handler is null, the
       *                                  listener is not null, and the calling thread has no looper.
       *
       * @see #capture
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see #abortCaptures
       */
      public abstract int captureBurst(@NonNull List<CaptureRequest> requests,
              @Nullable CaptureCallback listener, @Nullable Handler handler)
              throws CameraAccessException;
  
      /**
       * Submit a list of requests to be captured in sequence as a burst. The
       * burst will be captured in the minimum amount of time possible, and will
       * not be interleaved with requests submitted by other capture or repeat
       * calls.
       *
       * <p>The behavior of this method matches that of
       * {@link #captureBurst(List, CaptureCallback, Handler)},
       * except that it uses {@link java.util.concurrent.Executor} as an argument
       * instead of {@link android.os.Handler}.</p>
       *
       * @param requests the list of settings for this burst capture
       * @param executor the executor which will be used for invoking the listener.
       * @param listener The callback object to notify each time one of the
       * requests in the burst has been processed.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the requests target no Surfaces, or the requests target
       *                                  Surfaces not currently configured as outputs; or one of the
       *                                  requests targets a set of Surfaces that cannot be submitted
       *                                  simultaneously in a reprocessable capture session; or a
       *                                  reprocess capture request is submitted in a
       *                                  non-reprocessable capture session; or one of the reprocess
       *                                  capture requests was created with a
       *                                  {@link TotalCaptureResult} from a different session; or one
       *                                  of the captures targets a Surface in the middle of being
       *                                  {@link #prepare prepared}; or if the executor is null; or if
       *                                  the listener is null.
       *
       * @see #capture
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see #abortCaptures
       */
      public int captureBurstRequests(@NonNull List<CaptureRequest> requests,
              @NonNull @CallbackExecutor Executor executor, @NonNull CaptureCallback listener)
              throws CameraAccessException {
          throw new UnsupportedOperationException("Subclasses must override this method");
      }
  
      /**
       * Request endlessly repeating capture of images by this capture session.
       *
       * <p>With this method, the camera device will continually capture images
       * using the settings in the provided {@link CaptureRequest}, at the maximum
       * rate possible.</p>
       *
       * <p>Repeating requests are a simple way for an application to maintain a
       * preview or other continuous stream of frames, without having to
       * continually submit identical requests through {@link #capture}.</p>
       *
       * <p>Repeat requests have lower priority than those submitted
       * through {@link #capture} or {@link #captureBurst}, so if
       * {@link #capture} is called when a repeating request is active, the
       * capture request will be processed before any further repeating
       * requests are processed.<p>
       *
       * <p>To stop the repeating capture, call {@link #stopRepeating}. Calling
       * {@link #abortCaptures} will also clear the request.</p>
       *
       * <p>Calling this method will replace any earlier repeating request or
       * burst set up by this method or {@link #setRepeatingBurst}, although any
       * in-progress burst will be completed before the new repeat request will be
       * used.</p>
       *
       * <p>This method does not support reprocess capture requests because each reprocess
       * {@link CaptureRequest} must be created from the {@link TotalCaptureResult} that matches
       * the input image to be reprocessed. This is either the {@link TotalCaptureResult} of capture
       * that is sent for reprocessing, or one of the {@link TotalCaptureResult TotalCaptureResults}
       * of a set of captures, when data from the whole set is combined by the application into a
       * single reprocess input image. The request must be capturing images from the camera. If a
       * reprocess capture request is submitted, this method will throw IllegalArgumentException.</p>
       *
       * @param request the request to repeat indefinitely
       * @param listener The callback object to notify every time the
       * request finishes processing. If null, no metadata will be
       * produced for this stream of requests, although image data will
       * still be produced.
       * @param handler the handler on which the listener should be invoked, or
       * {@code null} to use the current thread's {@link android.os.Looper
       * looper}.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the request references no Surfaces or references Surfaces
       *                                  that are not currently configured as outputs; or the request
       *                                  is a reprocess capture request; or the capture targets a
       *                                  Surface in the middle of being {@link #prepare prepared}; or
       *                                  the handler is null, the listener is not null, and the
       *                                  calling thread has no looper; or no requests were passed in.
       *
       * @see #capture
       * @see #captureBurst
       * @see #setRepeatingBurst
       * @see #stopRepeating
       * @see #abortCaptures
       */
      public abstract int setRepeatingRequest(@NonNull CaptureRequest request,
              @Nullable CaptureCallback listener, @Nullable Handler handler)
              throws CameraAccessException;
  
      /**
       * Request endlessly repeating capture of images by this capture session.
       *
       * <p>The behavior of this method matches that of
       * {@link #setRepeatingRequest(CaptureRequest, CaptureCallback, Handler)},
       * except that it uses {@link java.util.concurrent.Executor} as an argument
       * instead of {@link android.os.Handler}.</p>
       *
       * @param request the request to repeat indefinitely
       * @param executor the executor which will be used for invoking the listener.
       * @param listener The callback object to notify every time the
       * request finishes processing.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the request references no Surfaces or references Surfaces
       *                                  that are not currently configured as outputs; or the request
       *                                  is a reprocess capture request; or the capture targets a
       *                                  Surface in the middle of being {@link #prepare prepared}; or
       *                                  the executor is null; or the listener is null.
       *
       * @see #capture
       * @see #captureBurst
       * @see #setRepeatingBurst
       * @see #stopRepeating
       * @see #abortCaptures
       */
      public int setSingleRepeatingRequest(@NonNull CaptureRequest request,
              @NonNull @CallbackExecutor Executor executor, @NonNull CaptureCallback listener)
              throws CameraAccessException {
          throw new UnsupportedOperationException("Subclasses must override this method");
      }
  
      /**
       * <p>Request endlessly repeating capture of a sequence of images by this
       * capture session.</p>
       *
       * <p>With this method, the camera device will continually capture images,
       * cycling through the settings in the provided list of
       * {@link CaptureRequest CaptureRequests}, at the maximum rate possible.</p>
       *
       * <p>If a request is submitted through {@link #capture} or
       * {@link #captureBurst}, the current repetition of the request list will be
       * completed before the higher-priority request is handled. This guarantees
       * that the application always receives a complete repeat burst captured in
       * minimal time, instead of bursts interleaved with higher-priority
       * captures, or incomplete captures.</p>
       *
       * <p>Repeating burst requests are a simple way for an application to
       * maintain a preview or other continuous stream of frames where each
       * request is different in a predicatable way, without having to continually
       * submit requests through {@link #captureBurst}.</p>
       *
       * <p>To stop the repeating capture, call {@link #stopRepeating}. Any
       * ongoing burst will still be completed, however. Calling
       * {@link #abortCaptures} will also clear the request.</p>
       *
       * <p>Calling this method will replace a previously-set repeating request or
       * burst set up by this method or {@link #setRepeatingRequest}, although any
       * in-progress burst will be completed before the new repeat burst will be
       * used.</p>
       *
       * <p>This method does not support reprocess capture requests because each reprocess
       * {@link CaptureRequest} must be created from the {@link TotalCaptureResult} that matches
       * the input image to be reprocessed. This is either the {@link TotalCaptureResult} of capture
       * that is sent for reprocessing, or one of the {@link TotalCaptureResult TotalCaptureResults}
       * of a set of captures, when data from the whole set is combined by the application into a
       * single reprocess input image. The request must be capturing images from the camera. If a
       * reprocess capture request is submitted, this method will throw IllegalArgumentException.</p>
       *
       * @param requests the list of requests to cycle through indefinitely
       * @param listener The callback object to notify each time one of the
       * requests in the repeating bursts has finished processing. If null, no
       * metadata will be produced for this stream of requests, although image
       * data will still be produced.
       * @param handler the handler on which the listener should be invoked, or
       * {@code null} to use the current thread's {@link android.os.Looper
       * looper}.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the requests reference no Surfaces or reference Surfaces
       *                                  not currently configured as outputs; or one of the requests
       *                                  is a reprocess capture request; or one of the captures
       *                                  targets a Surface in the middle of being
       *                                  {@link #prepare prepared}; or the handler is null, the
       *                                  listener is not null, and the calling thread has no looper;
       *                                  or no requests were passed in.
       *
       * @see #capture
       * @see #captureBurst
       * @see #setRepeatingRequest
       * @see #stopRepeating
       * @see #abortCaptures
       */
      public abstract int setRepeatingBurst(@NonNull List<CaptureRequest> requests,
              @Nullable CaptureCallback listener, @Nullable Handler handler)
              throws CameraAccessException;
  
      /**
       * <p>Request endlessly repeating capture of a sequence of images by this
       * capture session.</p>
       *
       * <p>The behavior of this method matches that of
       * {@link #setRepeatingBurst(List, CaptureCallback, Handler)},
       * except that it uses {@link java.util.concurrent.Executor} as an argument
       * instead of {@link android.os.Handler}.</p>
       *
       * @param requests the list of requests to cycle through indefinitely
       * @param executor the executor which will be used for invoking the listener.
       * @param listener The callback object to notify each time one of the
       * requests in the repeating bursts has finished processing.
       *
       * @return int A unique capture sequence ID used by
       *             {@link CaptureCallback#onCaptureSequenceCompleted}.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       * @throws IllegalArgumentException If the requests reference no Surfaces or reference Surfaces
       *                                  not currently configured as outputs; or one of the requests
       *                                  is a reprocess capture request; or one of the captures
       *                                  targets a Surface in the middle of being
       *                                  {@link #prepare prepared}; or the executor is null; or the
       *                                  listener is null.
       *
       * @see #capture
       * @see #captureBurst
       * @see #setRepeatingRequest
       * @see #stopRepeating
       * @see #abortCaptures
       */
      public int setRepeatingBurstRequests(@NonNull List<CaptureRequest> requests,
              @NonNull @CallbackExecutor Executor executor, @NonNull CaptureCallback listener)
              throws CameraAccessException {
          throw new UnsupportedOperationException("Subclasses must override this method");
      }
  
      /**
       * <p>Cancel any ongoing repeating capture set by either
       * {@link #setRepeatingRequest setRepeatingRequest} or
       * {@link #setRepeatingBurst}. Has no effect on requests submitted through
       * {@link #capture capture} or {@link #captureBurst captureBurst}.</p>
       *
       * <p>Any currently in-flight captures will still complete, as will any burst that is
       * mid-capture. To ensure that the device has finished processing all of its capture requests
       * and is in ready state, wait for the {@link StateCallback#onReady} callback after
       * calling this method.</p>
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       *
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see StateCallback#onReady
       */
      public abstract void stopRepeating() throws CameraAccessException;
  
      /**
       * Discard all captures currently pending and in-progress as fast as possible.
       *
       * <p>The camera device will discard all of its current work as fast as possible. Some in-flight
       * captures may complete successfully and call {@link CaptureCallback#onCaptureCompleted}, while
       * others will trigger their {@link CaptureCallback#onCaptureFailed} callbacks. If a repeating
       * request or a repeating burst is set, it will be cleared.</p>
       *
       * <p>This method is the fastest way to switch the camera device to a new session with
       * {@link CameraDevice#createCaptureSession} or
       * {@link CameraDevice#createReprocessableCaptureSession}, at the cost of discarding in-progress
       * work. It must be called before the new session is created. Once all pending requests are
       * either completed or thrown away, the {@link StateCallback#onReady} callback will be called,
       * if the session has not been closed. Otherwise, the {@link StateCallback#onClosed}
       * callback will be fired when a new session is created by the camera device.</p>
       *
       * <p>Cancelling will introduce at least a brief pause in the stream of data from the camera
       * device, since once the camera device is emptied, the first new request has to make it through
       * the entire camera pipeline before new output buffers are produced.</p>
       *
       * <p>This means that using {@code abortCaptures()} to simply remove pending requests is not
       * recommended; it's best used for quickly switching output configurations, or for cancelling
       * long in-progress requests (such as a multi-second capture).</p>
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       *
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       * @see CameraDevice#createCaptureSession
       * @see CameraDevice#createReprocessableCaptureSession
       */
      public abstract void abortCaptures() throws CameraAccessException;
  
      /**
       * Return if the application can submit reprocess capture requests with this camera capture
       * session.
       *
       * @return {@code true} if the application can submit reprocess capture requests with this
       *         camera capture session. {@code false} otherwise.
       *
       * @see CameraDevice#createReprocessableCaptureSession
       */
      public abstract boolean isReprocessable();
  
      /**
       * Get the input Surface associated with a reprocessable capture session.
       *
       * <p>Each reprocessable capture session has an input {@link Surface} where the reprocess
       * capture requests get the input images from, rather than the camera device. The application
       * can create a {@link android.media.ImageWriter ImageWriter} with this input {@link Surface}
       * and use it to provide input images for reprocess capture requests. When the reprocessable
       * capture session is closed, the input {@link Surface} is abandoned and becomes invalid.</p>
       *
       * @return The {@link Surface} where reprocessing capture requests get the input images from. If
       *         this is not a reprocess capture session, {@code null} will be returned.
       *
       * @see CameraDevice#createReprocessableCaptureSession
       * @see android.media.ImageWriter
       * @see android.media.ImageReader
       */
      @Nullable
      public abstract Surface getInputSurface();
  
      /**
       * Update {@link OutputConfiguration} after configuration finalization see
       * {@link #finalizeOutputConfigurations}.
       *
       * <p>Any {@link OutputConfiguration} that has been modified via calls to
       * {@link OutputConfiguration#addSurface} or {@link OutputConfiguration#removeSurface} must be
       * updated. After the update call returns without throwing exceptions any newly added surfaces
       * can be referenced in subsequent capture requests.</p>
       *
       * <p>Surfaces that get removed must not be part of any active repeating or single/burst
       * request or have any pending results. Consider updating any repeating requests first via
       * {@link #setRepeatingRequest} or {@link #setRepeatingBurst} and then wait for the last frame
       * number when the sequence completes {@link CaptureCallback#onCaptureSequenceCompleted}
       * before calling updateOutputConfiguration to remove a previously active Surface.</p>
       *
       * <p>Surfaces that get added must not be part of any other registered
       * {@link OutputConfiguration}.</p>
       *
       * @param config Modified output configuration.
       *
       * @throws CameraAccessException if the camera device is no longer connected or has
       *                               encountered a fatal error.
       * @throws IllegalArgumentException if an attempt was made to add a {@link Surface} already
       *                               in use by another buffer-producing API, such as MediaCodec or
       *                               a different camera device or {@link OutputConfiguration}; or
       *                               new surfaces are not compatible (see
       *                               {@link OutputConfiguration#enableSurfaceSharing}); or a
       *                               {@link Surface} that was removed from the modified
       *                               {@link OutputConfiguration} still has pending requests.
       * @throws IllegalStateException if this session is no longer active, either because the session
       *                               was explicitly closed, a new session has been created
       *                               or the camera device has been closed.
       */
      public void updateOutputConfiguration(OutputConfiguration config)
          throws CameraAccessException {
          throw new UnsupportedOperationException("Subclasses must override this method");
      }
  
      /**
       * Close this capture session asynchronously.
       *
       * <p>Closing a session frees up the target output Surfaces of the session for reuse with either
       * a new session, or to other APIs that can draw to Surfaces.</p>
       *
       * <p>Note that creating a new capture session with {@link CameraDevice#createCaptureSession}
       * will close any existing capture session automatically, and call the older session listener's
       * {@link StateCallback#onClosed} callback. Using {@link CameraDevice#createCaptureSession}
       * directly without closing is the recommended approach for quickly switching to a new session,
       * since unchanged target outputs can be reused more efficiently.</p>
       *
       * <p>Once a session is closed, all methods on it will throw an IllegalStateException, and any
       * repeating requests or bursts are stopped (as if {@link #stopRepeating()} was called).
       * However, any in-progress capture requests submitted to the session will be completed as
       * normal; once all captures have completed and the session has been torn down,
       * {@link StateCallback#onClosed} will be called.</p>
       *
       * <p>Closing a session is idempotent; closing more than once has no effect.</p>
       */
      @Override
      public abstract void close();
  
      /**
       * A callback object for receiving updates about the state of a camera capture session.
       *
       */
      public static abstract class StateCallback {
  
          /**
           * This method is called when the camera device has finished configuring itself, and the
           * session can start processing capture requests.
           *
           * <p>If there are capture requests already queued with the session, they will start
           * processing once this callback is invoked, and the session will call {@link #onActive}
           * right after this callback is invoked.</p>
           *
           * <p>If no capture requests have been submitted, then the session will invoke
           * {@link #onReady} right after this callback.</p>
           *
           * <p>If the camera device configuration fails, then {@link #onConfigureFailed} will
           * be invoked instead of this callback.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           */
          public abstract void onConfigured(@NonNull CameraCaptureSession session);
  
          /**
           * This method is called if the session cannot be configured as requested.
           *
           * <p>This can happen if the set of requested outputs contains unsupported sizes,
           * or too many outputs are requested at once.</p>
           *
           * <p>The session is considered to be closed, and all methods called on it after this
           * callback is invoked will throw an IllegalStateException. Any capture requests submitted
           * to the session prior to this callback will be discarded and will not produce any
           * callbacks on their listeners.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           */
          public abstract void onConfigureFailed(@NonNull CameraCaptureSession session);
  
          /**
           * This method is called every time the session has no more capture requests to process.
           *
           * <p>During the creation of a new session, this callback is invoked right after
           * {@link #onConfigured} if no capture requests were submitted to the session prior to it
           * completing configuration.</p>
           *
           * <p>Otherwise, this callback will be invoked any time the session finishes processing
           * all of its active capture requests, and no repeating request or burst is set up.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           *
           */
          public void onReady(@NonNull CameraCaptureSession session) {
              // default empty implementation
          }
  
          /**
           * This method is called when the session starts actively processing capture requests.
           *
           * <p>If capture requests are submitted prior to {@link #onConfigured} being called,
           * then the session will start processing those requests immediately after the callback,
           * and this method will be immediately called after {@link #onConfigured}.
           *
           * <p>If the session runs out of capture requests to process and calls {@link #onReady},
           * then this callback will be invoked again once new requests are submitted for capture.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           */
          public void onActive(@NonNull CameraCaptureSession session) {
              // default empty implementation
          }
  
          /**
           * This method is called when camera device's input capture queue becomes empty,
           * and is ready to accept the next request.
           *
           * <p>Pending capture requests exist in one of two queues: the in-flight queue where requests
           * are already in different stages of processing pipeline, and an input queue where requests
           * wait to enter the in-flight queue. The input queue is needed because more requests may be
           * submitted than the current camera device pipeline depth.</p>
           *
           * <p>This callback is fired when the input queue becomes empty, and the camera device may
           * have to fall back to the repeating request if set, or completely skip the next frame from
           * the sensor. This can cause glitches to camera preview output, for example. This callback
           * will only fire after requests queued by capture() or captureBurst(), not after a
           * repeating request or burst enters the in-flight queue. For example, in the common case
           * of a repeating request and a single-shot JPEG capture, this callback only fires when the
           * JPEG request has entered the in-flight queue for capture.</p>
           *
           * <p>By only sending a new {@link #capture} or {@link #captureBurst} when the input
           * queue is empty, pipeline latency can be minimized.</p>
           *
           * <p>This callback is not fired when the session is first created. It is different from
           * {@link #onReady}, which is fired when all requests in both queues have been processed.</p>
           *
           * @param session
           *            The session returned by {@link CameraDevice#createCaptureSession}
           */
          public void onCaptureQueueEmpty(@NonNull CameraCaptureSession session) {
              // default empty implementation
          }
  
          /**
           * This method is called when the session is closed.
           *
           * <p>A session is closed when a new session is created by the parent camera device,
           * or when the parent camera device is closed (either by the user closing the device,
           * or due to a camera device disconnection or fatal error).</p>
           *
           * <p>Once a session is closed, all methods on it will throw an IllegalStateException, and
           * any repeating requests or bursts are stopped (as if {@link #stopRepeating()} was called).
           * However, any in-progress capture requests submitted to the session will be completed
           * as normal.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           */
          public void onClosed(@NonNull CameraCaptureSession session) {
              // default empty implementation
          }
  
          /**
           * This method is called when the buffer pre-allocation for an output Surface is complete.
           *
           * <p>Buffer pre-allocation for an output Surface is started by the {@link #prepare} call.
           * While allocation is underway, the Surface must not be used as a capture target.
           * Once this callback fires, the output Surface provided can again be used as a target for
           * a capture request.</p>
           *
           * <p>In case of a error during pre-allocation (such as running out of suitable memory),
           * this callback is still invoked after the error is encountered, though some buffers may
           * not have been successfully pre-allocated.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           * @param surface the Surface that was used with the {@link #prepare} call.
           */
          public void onSurfacePrepared(@NonNull CameraCaptureSession session,
                  @NonNull Surface surface) {
              // default empty implementation
          }
      }
  
      /**
       * <p>A callback object for tracking the progress of a {@link CaptureRequest} submitted to the
       * camera device.</p>
       *
       * <p>This callback is invoked when a request triggers a capture to start,
       * and when the capture is complete. In case on an error capturing an image,
       * the error method is triggered instead of the completion method.</p>
       *
       * @see #capture
       * @see #captureBurst
       * @see #setRepeatingRequest
       * @see #setRepeatingBurst
       */
      public static abstract class CaptureCallback {
  
          /**
           * This constant is used to indicate that no images were captured for
           * the request.
           *
           * @hide
           */
          public static final int NO_FRAMES_CAPTURED = -1;
  
          /**
           * This method is called when the camera device has started capturing
           * the output image for the request, at the beginning of image exposure, or
           * when the camera device has started processing an input image for a reprocess
           * request.
           *
           * <p>For a regular capture request, this callback is invoked right as
           * the capture of a frame begins, so it is the most appropriate time
           * for playing a shutter sound, or triggering UI indicators of capture.</p>
           *
           * <p>The request that is being used for this capture is provided, along
           * with the actual timestamp for the start of exposure. For a reprocess
           * request, this timestamp will be the input image's start of exposure
           * which matches {@link CaptureResult#SENSOR_TIMESTAMP the result timestamp field}
           * of the {@link TotalCaptureResult} that was used to
           * {@link CameraDevice#createReprocessCaptureRequest create the reprocess request}.
           * This timestamp matches the timestamps that will be
           * included in {@link CaptureResult#SENSOR_TIMESTAMP the result timestamp field},
           * and in the buffers sent to each output Surface. These buffer
           * timestamps are accessible through, for example,
           * {@link android.media.Image#getTimestamp() Image.getTimestamp()} or
           * {@link android.graphics.SurfaceTexture#getTimestamp()}.
           * The frame number included is equal to the frame number that will be included in
           * {@link CaptureResult#getFrameNumber}.</p>
           *
           * <p>For the simplest way to play a shutter sound camera shutter or a
           * video recording start/stop sound, see the
           * {@link android.media.MediaActionSound} class.</p>
           *
           * <p>The default implementation of this method does nothing.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           * @param request the request for the capture that just begun
           * @param timestamp the timestamp at start of capture for a regular request, or
           *                  the timestamp at the input image's start of capture for a
           *                  reprocess request, in nanoseconds.
           * @param frameNumber the frame number for this capture
           *
           * @see android.media.MediaActionSound
           */
          public void onCaptureStarted(@NonNull CameraCaptureSession session,
                  @NonNull CaptureRequest request, long timestamp, long frameNumber) {
              // default empty implementation
          }
  
          /**
           * This method is called when some results from an image capture are
           * available.
           *
           * <p>The result provided here will contain some subset of the fields of
           * a full result. Multiple onCapturePartial calls may happen per
           * capture; a given result field will only be present in one partial
           * capture at most. The final onCaptureCompleted call will always
           * contain all the fields, whether onCapturePartial was called or
           * not.</p>
           *
           * <p>The default implementation of this method does nothing.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           * @param request The request that was given to the CameraDevice
           * @param result The partial output metadata from the capture, which
           * includes a subset of the CaptureResult fields.
           *
           * @see #capture
           * @see #captureBurst
           * @see #setRepeatingRequest
           * @see #setRepeatingBurst
           *
           * @hide
           */
          public void onCapturePartial(CameraCaptureSession session,
                  CaptureRequest request, CaptureResult result) {
              // default empty implementation
          }
  
          /**
           * This method is called when an image capture makes partial forward progress; some
           * (but not all) results from an image capture are available.
           *
           * <p>The result provided here will contain some subset of the fields of
           * a full result. Multiple {@link #onCaptureProgressed} calls may happen per
           * capture; a given result field will only be present in one partial
           * capture at most. The final {@link #onCaptureCompleted} call will always
           * contain all the fields (in particular, the union of all the fields of all
           * the partial results composing the total result).</p>
           *
           * <p>For each request, some result data might be available earlier than others. The typical
           * delay between each partial result (per request) is a single frame interval.
           * For performance-oriented use-cases, applications should query the metadata they need
           * to make forward progress from the partial results and avoid waiting for the completed
           * result.</p>
           *
           * <p>For a particular request, {@link #onCaptureProgressed} may happen before or after
           * {@link #onCaptureStarted}.</p>
           *
           * <p>Each request will generate at least {@code 1} partial results, and at most
           * {@link CameraCharacteristics#REQUEST_PARTIAL_RESULT_COUNT} partial results.</p>
           *
           * <p>Depending on the request settings, the number of partial results per request
           * will vary, although typically the partial count could be the same as long as the
           * camera device subsystems enabled stay the same.</p>
           *
           * <p>The default implementation of this method does nothing.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           * @param request The request that was given to the CameraDevice
           * @param partialResult The partial output metadata from the capture, which
           * includes a subset of the {@link TotalCaptureResult} fields.
           *
           * @see #capture
           * @see #captureBurst
           * @see #setRepeatingRequest
           * @see #setRepeatingBurst
           */
          public void onCaptureProgressed(@NonNull CameraCaptureSession session,
                  @NonNull CaptureRequest request, @NonNull CaptureResult partialResult) {
              // default empty implementation
          }
  
          /**
           * This method is called when an image capture has fully completed and all the
           * result metadata is available.
           *
           * <p>This callback will always fire after the last {@link #onCaptureProgressed};
           * in other words, no more partial results will be delivered once the completed result
           * is available.</p>
           *
           * <p>For performance-intensive use-cases where latency is a factor, consider
           * using {@link #onCaptureProgressed} instead.</p>
           *
           * <p>The default implementation of this method does nothing.</p>
           *
           * @param session the session returned by {@link CameraDevice#createCaptureSession}
           * @param request The request that was given to the CameraDevice
           * @param result The total output metadata from the capture, including the
           * final capture parameters and the state of the camera system during
           * capture.
           *
           * @see #capture
           * @see #captureBurst
           * @see #setRepeatingRequest
           * @see #setRepeatingBurst
           */
          public void onCaptureCompleted(@NonNull CameraCaptureSession session,
                  @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
              // default empty implementation
          }
  
          /**
           * This method is called instead of {@link #onCaptureCompleted} when the
           * camera device failed to produce a {@link CaptureResult} for the
           * request.
           *
           * <p>Other requests are unaffected, and some or all image buffers from
           * the capture may have been pushed to their respective output
           * streams.</p>
           *
           * <p>The default implementation of this method does nothing.</p>
           *
           * @param session
           *            The session returned by {@link CameraDevice#createCaptureSession}
           * @param request
           *            The request that was given to the CameraDevice
           * @param failure
           *            The output failure from the capture, including the failure reason
           *            and the frame number.
           *
           * @see #capture
           * @see #captureBurst
           * @see #setRepeatingRequest
           * @see #setRepeatingBurst
           */
          public void onCaptureFailed(@NonNull CameraCaptureSession session,
                  @NonNull CaptureRequest request, @NonNull CaptureFailure failure) {
              // default empty implementation
          }
  
          /**
           * This method is called independently of the others in CaptureCallback,
           * when a capture sequence finishes and all {@link CaptureResult}
           * or {@link CaptureFailure} for it have been returned via this listener.
           *
           * <p>In total, there will be at least one result/failure returned by this listener
           * before this callback is invoked. If the capture sequence is aborted before any
           * requests have been processed, {@link #onCaptureSequenceAborted} is invoked instead.</p>
           *
           * <p>The default implementation does nothing.</p>
           *
           * @param session
           *            The session returned by {@link CameraDevice#createCaptureSession}
           * @param sequenceId
           *            A sequence ID returned by the {@link #capture} family of functions.
           * @param frameNumber
           *            The last frame number (returned by {@link CaptureResult#getFrameNumber}
           *            or {@link CaptureFailure#getFrameNumber}) in the capture sequence.
           *
           * @see CaptureResult#getFrameNumber()
           * @see CaptureFailure#getFrameNumber()
           * @see CaptureResult#getSequenceId()
           * @see CaptureFailure#getSequenceId()
           * @see #onCaptureSequenceAborted
           */
          public void onCaptureSequenceCompleted(@NonNull CameraCaptureSession session,
                  int sequenceId, long frameNumber) {
              // default empty implementation
          }
  
          /**
           * This method is called independently of the others in CaptureCallback,
           * when a capture sequence aborts before any {@link CaptureResult}
           * or {@link CaptureFailure} for it have been returned via this listener.
           *
           * <p>Due to the asynchronous nature of the camera device, not all submitted captures
           * are immediately processed. It is possible to clear out the pending requests
           * by a variety of operations such as {@link CameraCaptureSession#stopRepeating} or
           * {@link CameraCaptureSession#abortCaptures}. When such an event happens,
           * {@link #onCaptureSequenceCompleted} will not be called.</p>
           *
           * <p>The default implementation does nothing.</p>
           *
           * @param session
           *            The session returned by {@link CameraDevice#createCaptureSession}
           * @param sequenceId
           *            A sequence ID returned by the {@link #capture} family of functions.
           *
           * @see CaptureResult#getFrameNumber()
           * @see CaptureFailure#getFrameNumber()
           * @see CaptureResult#getSequenceId()
           * @see CaptureFailure#getSequenceId()
           * @see #onCaptureSequenceCompleted
           */
          public void onCaptureSequenceAborted(@NonNull CameraCaptureSession session,
                  int sequenceId) {
              // default empty implementation
          }
  
          /**
           * <p>This method is called if a single buffer for a capture could not be sent to its
           * destination surface.</p>
           *
           * <p>If the whole capture failed, then {@link #onCaptureFailed} will be called instead. If
           * some but not all buffers were captured but the result metadata will not be available,
           * then onCaptureFailed will be invoked with {@link CaptureFailure#wasImageCaptured}
           * returning true, along with one or more calls to {@link #onCaptureBufferLost} for the
           * failed outputs.</p>
           *
           * @param session
           *            The session returned by {@link CameraDevice#createCaptureSession}
           * @param request
           *            The request that was given to the CameraDevice
           * @param target
           *            The target Surface that the buffer will not be produced for
           * @param frameNumber
           *            The frame number for the request
           */
          public void onCaptureBufferLost(@NonNull CameraCaptureSession session,
                  @NonNull CaptureRequest request, @NonNull Surface target, long frameNumber) {
              // default empty implementation
          }
      }
  
  }
  