gecko-dev/image/public/imgIDecoderObserver.idl

/** -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "imgIContainerObserver.idl"

interface imgIRequest;
interface imgIContainer;

%{C++
#include "nsRect.h"
%}

/**
 * imgIDecoderObserver interface
 *
 * This interface is used both for observing imgIDecoder objects and for
 * observing imgIRequest objects.  In the former case, aRequest is
 * always null.
 *
 * We make the distinction here between "load" and "decode" notifications. Load
 * notifications are fired as the image is loaded from the network or
 * filesystem. Decode notifications are fired as the image is decoded. If an
 * image is decoded on load and not visibly discarded, decode notifications are
 * nested logically inside load notifications as one might expect. However, with
 * decode-on-draw, the set of decode notifications can imgRcome completely _after_
 * the load notifications, and can come multiple times if the image is
 * discardable. Moreover, they can be interleaved in various ways. In general,
 * any presumed ordering between load and decode notifications should not be
 * relied upon.
 *
 * Decode notifications may or may not be synchronous, depending on the
 * situation. If imgIDecoder::FLAG_SYNC_DECODE is passed to a function that
 * triggers a decode, all notifications that can be generated from the currently
 * loaded data fire before the call returns. If FLAG_SYNC_DECODE is not passed,
 * all, some, or none of the notifications may fire before the call returns.
 *
 * This interface will be cleaned up in bug 505385.
 *
 * @author Stuart Parmenter <pavlov@netscape.com>
 * @version 0.1
 * @see imagelib2
 */
[scriptable, uuid(5ca71b89-1a2f-475f-881d-d76c1531c4c8)]
interface imgIDecoderObserver : imgIContainerObserver
{
  /**
   * Load notification.
   *
   * called at the same time that nsIRequestObserver::onStartRequest would be
   * (used only for observers of imgIRequest objects, which are nsIRequests,
   * not imgIDecoder objects)
   */
  void onStartRequest(in imgIRequest aRequest);

  /**
   * Decode notification.
   *
   * Called as soon as the image begins getting decoded. This does not include
   * "header-only" decodes used by decode-on-draw to parse the width/height
   * out of the image. Thus, it is a decode notification only.
   */
  void onStartDecode(in imgIRequest aRequest);

  /**
   * Load notification.
   *
   * Called once enough data has been loaded from the network that we were able
   * to parse the width/height from the image. By the time this callback is been
   * called, the size has been set on the container and STATUS_SIZE_AVAILABLE
   * has been set on the associated imgRequest.
   */
  void onStartContainer(in imgIRequest aRequest, in imgIContainer aContainer);

  /**
   * Decode notification.
   *
   * called when each frame is created.
   */
  void onStartFrame(in imgIRequest aRequest, in unsigned long aFrame);

  /**
   * Decode notification.
   *
   * called when there is more to paint.
   */
  [noscript] void onDataAvailable(in imgIRequest aRequest, in boolean aCurrentFrame, [const] in nsIntRect aRect);

  /**
   * Decode notification.
   *
   * called when a frame is finished decoding.
   */
  void onStopFrame(in imgIRequest aRequest, in unsigned long aFrame);

  /**
   * Do not implement this. It is useless and going away.
   */
  void onStopContainer(in imgIRequest aRequest, in imgIContainer aContainer);

  /**
   * Notification for when an image is known to be animated. This should be
   * fired at the earliest possible time.
   */
  void onImageIsAnimated(in imgIRequest aRequest);

  /**
   * In theory a decode notification, but currently a load notification.
   *
   * Ideally this would be called when the decode is complete. Unfortunately,
   * this is currently the only way to signal decoding errors to consumers,
   * and the only decoding errors that consumers care about (indeed, the only
   * ones that they're prepared to hear about) are failures to instantiate the
   * decoder (<img src="foo.html"> for example). Thus, currently this is just
   * a companion to onStopDecode to signal success or failure. This will be
   * revisited in bug 505385. If you're thinking of doing something new with
   * this, please talk to bholley first.
   */
  void onStopDecode(in imgIRequest aRequest, in nsresult status,
                    in wstring statusArg);

  /**
   * Load notification.
   *
   * called at the same time that nsIRequestObserver::onStopRequest would be
   * (used only for observers of imgIRequest objects, which are nsIRequests,
   * not imgIDecoder objects)
   */
  void onStopRequest(in imgIRequest aRequest, in boolean aIsLastPart);

  /**
   * Called when the decoded image data is discarded. This means that the frames
   * no longer exist in decoded form, and any attempt to access or draw the
   * image will initiate a new series of progressive decode notifications.
   */
  void onDiscard(in imgIRequest aRequest);

};