diff -r 000000000000 -r 6474c204b198 image/src/imgDecoderObserver.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/image/src/imgDecoderObserver.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,139 @@
+/** -*- 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/. */
+
+#ifndef MOZILLA_IMAGELIB_IMGDECODEROBSERVER_H_
+#define MOZILLA_IMAGELIB_IMGDECODEROBSERVER_H_
+
+#include "nsRect.h"
+#include "mozilla/WeakPtr.h"
+
+struct nsIntRect;
+
+/**
+ * imgDecoderObserver interface
+ *
+ * This interface is used to observe Decoder objects.
+ *
+ * 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 come 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.
+ */
+class imgDecoderObserver
+{
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(imgDecoderObserver);
+
+  /**
+   * 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)
+   */
+  virtual void OnStartRequest() = 0;
+
+  /**
+   * 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.
+   */
+  virtual void OnStartDecode() = 0;
+
+  /**
+   * 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.
+   */
+  virtual void OnStartContainer() = 0;
+
+  /**
+   * Decode notification.
+   *
+   * Called when we know a frame has begun decoding.
+   */
+  virtual void OnStartFrame() = 0;
+
+  /**
+   * Decode notification.
+   *
+   * called when there is more to paint.
+   */
+  virtual void FrameChanged(const nsIntRect * aDirtyRect) = 0;
+
+  /**
+   * Decode notification.
+   *
+   * called when a frame is finished decoding.
+   */
+  virtual void OnStopFrame() = 0;
+
+  /**
+   * Notification for when an image is known to be animated. This should be
+   * fired at the earliest possible time.
+   */
+  virtual void OnImageIsAnimated() = 0;
+
+  /**
+   * Decode notification.
+   *
+   * Called when all decoding has terminated.
+   */
+  virtual void OnStopDecode(nsresult status) = 0;
+
+  /**
+   * 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)
+   */
+  virtual void OnStopRequest(bool aIsLastPart, nsresult aStatus) = 0;
+
+  /**
+   * 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.
+   */
+  virtual void OnDiscard() = 0;
+
+  /**
+   * Called when we are asked to Draw an image that is not locked.
+   */
+  virtual void OnUnlockedDraw() = 0;
+
+  /**
+   * Called when an image is realized to be in error state.
+   */
+  virtual void OnError() = 0;
+
+protected:
+  virtual ~imgDecoderObserver() = 0;
+};
+
+// We must define a destructor because derived classes call our destructor from
+// theirs.  Pure virtual destructors only requires that child classes implement
+// a virtual destructor, not that we can't have one too!
+inline imgDecoderObserver::~imgDecoderObserver()
+{}
+
+#endif // MOZILLA_IMAGELIB_IMGDECODEROBSERVER_H