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 /* -*- Mode: C++; tab-width: 20; 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 GFX_READBACKLAYER_H

 #define GFX_READBACKLAYER_H

 #include <stdint.h>                     // for uint64_t

 #include "Layers.h"                     // for Layer, etc

 #include "gfxColor.h"                   // for gfxRGBA

 #include "gfxRect.h"                    // for gfxRect

 #include "mozilla/mozalloc.h"           // for operator delete

 #include "nsAutoPtr.h"                  // for nsAutoPtr

 #include "nsCOMPtr.h"                   // for already_AddRefed

 #include "nsDebug.h"                    // for NS_ASSERTION

 #include "nsPoint.h"                    // for nsIntPoint

 #include "nsRect.h"                     // for nsIntRect

 #include "nsSize.h"                     // for nsIntSize

 #include "nscore.h"                     // for nsACString

 class gfxContext;

 namespace mozilla {

 namespace layers {

 class ReadbackProcessor;

 /**

  * A ReadbackSink receives a stream of updates to a rectangle of pixels.

  * These update callbacks are always called on the main thread, either during

  * EndTransaction or from the event loop.

  */

 class ReadbackSink {

 public:

   ReadbackSink() {}

   virtual ~ReadbackSink() {}

   /**

    * Sends an update to indicate that the background is currently unknown.

    */

   virtual void SetUnknown(uint64_t aSequenceNumber) = 0;

   /**

    * Called by the layer system to indicate that the contents of part of

    * the readback area are changing.

    * @param aRect is the rectangle of content that is being updated,

    * in the coordinate system of the ReadbackLayer.

    * @param aSequenceNumber updates issued out of order should be ignored.

    * Only use updates whose sequence counter is greater than all other updates

    * seen so far. Return null when a non-fresh sequence value is given.

    * @return a context into which the update should be drawn. This should be

    * set up to clip to aRect. Zero should never be passed as a sequence number.

    * If this returns null, EndUpdate should NOT be called. If it returns

    * non-null, EndUpdate must be called.

    *

    * We don't support partially unknown backgrounds. Therefore, the

    * first BeginUpdate after a SetUnknown will have the complete background.

    */

   virtual already_AddRefed<gfxContext>

       BeginUpdate(const nsIntRect& aRect, uint64_t aSequenceNumber) = 0;

   /**

    * EndUpdate must be called immediately after BeginUpdate, without returning

    * to the event loop.

    * @param aContext the context returned by BeginUpdate

    * Implicitly Restore()s the state of aContext.

    */

   virtual void EndUpdate(gfxContext* aContext, const nsIntRect& aRect) = 0;

 };

 /**

  * A ReadbackLayer never renders anything. It enables clients to extract

  * the rendered contents of the layer tree below the ReadbackLayer.

  * The rendered contents are delivered asynchronously via calls to a

  * ReadbackSink object supplied by the client.

  *

  * This is a "best effort" API; it is possible for the layer system to tell

  * the ReadbackSink that the contents of the readback area are unknown.

  *

  * This API exists to work around the limitations of transparent windowless

  * plugin rendering APIs. It should not be used for anything else.

  */

 class ReadbackLayer : public Layer {

 public:

   MOZ_LAYER_DECL_NAME("ReadbackLayer", TYPE_READBACK)

   virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface)

   {

     // Snap our local transform first, and snap the inherited transform as well.

     // This makes our snapping equivalent to what would happen if our content

     // was drawn into a ThebesLayer (gfxContext would snap using the local

     // transform, then we'd snap again when compositing the ThebesLayer).

     mEffectiveTransform =

         SnapTransform(GetLocalTransform(), gfxRect(0, 0, mSize.width, mSize.height),

                       nullptr)*

         SnapTransformTranslation(aTransformToSurface, nullptr);

   }

   /**

    * CONSTRUCTION PHASE ONLY

    * Set the callback object to which readback updates will be delivered.

    * This also resets the "needed rectangle" so that on the next layer tree

    * transaction we will try to deliver the full contents of the readback

    * area to the sink.

    * This layer takes ownership of the sink. It will be deleted when the

    * layer is destroyed or when a new sink is set.

    * Initially the contents of the readback area are completely unknown.

    */

   void SetSink(ReadbackSink* aSink)

   {

     SetUnknown();

     mSink = aSink;

   }

   ReadbackSink* GetSink() { return mSink; }

   /**

    * CONSTRUCTION PHASE ONLY

    * Set the size of content that should be read back. The readback area

    * has its top-left at 0,0 and has size aSize.

    * Can only be called while the sink is null!

    */

   void SetSize(const nsIntSize& aSize)

   {

     NS_ASSERTION(!mSink, "Should have no sink while changing size!");

     mSize = aSize;

   }

   const nsIntSize& GetSize() { return mSize; }

   nsIntRect GetRect() { return nsIntRect(nsIntPoint(0, 0), mSize); }

   bool IsBackgroundKnown()

   {

     return mBackgroundLayer || mBackgroundColor.a == 1.0;

   }

   void NotifyRemoved() {

     SetUnknown();

     mSink = nullptr;

   }

   void NotifyThebesLayerRemoved(ThebesLayer* aLayer)

   {

     if (mBackgroundLayer == aLayer) {

       mBackgroundLayer = nullptr;

     }

   }

   const nsIntPoint& GetBackgroundLayerOffset() { return mBackgroundLayerOffset; }

   uint64_t AllocateSequenceNumber() { return ++mSequenceCounter; }

   void SetUnknown()

   {

     if (IsBackgroundKnown()) {

       if (mSink) {

         mSink->SetUnknown(AllocateSequenceNumber());

       }

       mBackgroundLayer = nullptr;

       mBackgroundColor = gfxRGBA(0,0,0,0);

     }

   }

 protected:

   friend class ReadbackProcessor;

   ReadbackLayer(LayerManager* aManager, void* aImplData) :

     Layer(aManager, aImplData),

     mSequenceCounter(0),

     mSize(0,0),

     mBackgroundLayer(nullptr),

     mBackgroundLayerOffset(0, 0),

     mBackgroundColor(gfxRGBA(0,0,0,0))

   {}

   // Print interesting information about this into aTo.  Internally

   // used to implement Dump*() and Log*().

   virtual nsACString& PrintInfo(nsACString& aTo, const char* aPrefix);

   uint64_t mSequenceCounter;

   nsAutoPtr<ReadbackSink> mSink;

   nsIntSize mSize;

   // This can refer to any (earlier) sibling ThebesLayer. That ThebesLayer

   // must have mUsedForReadback set on it. If the ThebesLayer is removed

   // for the container, this will be set to null by NotifyThebesLayerRemoved.

   // This ThebesLayer contains the contents which have previously been reported

   // to mSink. The ThebesLayer had only an integer translation transform,

   // and it covered the entire readback area. This layer also had only an

   // integer translation transform.

   ThebesLayer* mBackgroundLayer;

   // When mBackgroundLayer is non-null, this is the offset to add to

   // convert from the coordinates of mBackgroundLayer to the coordinates

   // of this layer.

   nsIntPoint   mBackgroundLayerOffset;

   // When mBackgroundColor is opaque, this is the color of the ColorLayer

   // that contained the contents we reported to mSink, which covered the

   // entire readback area.

   gfxRGBA      mBackgroundColor;

 };

 }

 }

 #endif /* GFX_READBACKLAYER_H */