diff --git a/include/gui/BufferQueue.h b/include/gui/BufferQueue.h
index 6c38cde..e7fac3d 100644
--- a/include/gui/BufferQueue.h
+++ b/include/gui/BufferQueue.h
@@ -170,6 +170,7 @@
            mFrameNumber(0),
            mBuf(INVALID_BUFFER_SLOT) {
              mCrop.makeInvalid();
+             mActiveRect.makeInvalid();
          }
         // mGraphicBuffer points to the buffer allocated for this slot or is NULL
         // if no buffer has been allocated.
@@ -191,9 +192,13 @@
         // mFrameNumber is the number of the queued frame for this slot.
         uint64_t mFrameNumber;
 
-        // buf is the slot index of this buffer
+        // mBuf is the slot index of this buffer
         int mBuf;
 
+        // mActiveRect is the active rectangle for the buffer.  Pixels outside
+        // this rectangle are considered completely transparent for the purposes
+        // of window composition.
+        Rect mActiveRect;
     };
 
     // The following public functions is the consumer facing interface
@@ -297,6 +302,7 @@
           mAcquireCalled(false),
           mNeedsCleanupOnRelease(false) {
             mCrop.makeInvalid();
+            mActiveRect.makeInvalid();
         }
 
         // mGraphicBuffer points to the buffer allocated for this slot or is NULL
@@ -353,6 +359,12 @@
         // mCrop is the current crop rectangle for this buffer slot.
         Rect mCrop;
 
+        // mActiveRect is the current active rectangle for this buffer slot.
+        // Pixels outside of this rectangle are to be treated as completely
+        // transparent during window composition.  The rectangle is in buffer
+        // pixel coordinates.
+        Rect mActiveRect;
+
         // mTransform is the current transform flags for this buffer slot.
         uint32_t mTransform;
 
diff --git a/include/gui/ISurfaceTexture.h b/include/gui/ISurfaceTexture.h
index 1e33764..7abc7db 100644
--- a/include/gui/ISurfaceTexture.h
+++ b/include/gui/ISurfaceTexture.h
@@ -86,21 +86,25 @@
     // QueueBufferInput must be a POD structure
     struct QueueBufferInput {
         inline QueueBufferInput(int64_t timestamp,
-                const Rect& crop, int scalingMode, uint32_t transform)
+                const Rect& crop, int scalingMode, uint32_t transform,
+                const Rect& activeRect)
         : timestamp(timestamp), crop(crop), scalingMode(scalingMode),
-          transform(transform) { }
+          transform(transform), activeRect(activeRect) { }
         inline void deflate(int64_t* outTimestamp, Rect* outCrop,
-                int* outScalingMode, uint32_t* outTransform) const {
+                int* outScalingMode, uint32_t* outTransform,
+                Rect* outActiveRect) const {
             *outTimestamp = timestamp;
             *outCrop = crop;
             *outScalingMode = scalingMode;
             *outTransform = transform;
+            *outActiveRect = activeRect;
         }
     private:
         int64_t timestamp;
         Rect crop;
         int scalingMode;
         uint32_t transform;
+        Rect activeRect;
     };
 
     // QueueBufferOutput must be a POD structure
diff --git a/include/gui/SurfaceTexture.h b/include/gui/SurfaceTexture.h
index f4ed226..7540ed8 100644
--- a/include/gui/SurfaceTexture.h
+++ b/include/gui/SurfaceTexture.h
@@ -151,13 +151,16 @@
     // texture as returned by updateTexImage().
     GLenum getCurrentTextureTarget() const;
 
-    // getCurrentCrop returns the cropping rectangle of the current buffer
+    // getCurrentCrop returns the cropping rectangle of the current buffer.
     Rect getCurrentCrop() const;
 
-    // getCurrentTransform returns the transform of the current buffer
+    // getCurrentActiveRect returns the active rectangle of the current buffer.
+    Rect getCurrentActiveRect() const;
+
+    // getCurrentTransform returns the transform of the current buffer.
     uint32_t getCurrentTransform() const;
 
-    // getCurrentScalingMode returns the scaling mode of the current buffer
+    // getCurrentScalingMode returns the scaling mode of the current buffer.
     uint32_t getCurrentScalingMode() const;
 
     // isSynchronousMode returns whether the SurfaceTexture is currently in
@@ -270,6 +273,12 @@
     // It gets set each time updateTexImage is called.
     Rect mCurrentCrop;
 
+    // mCurrentActiveRect is the active rectangle that applies to the current
+    // texture.  It gets set each time updateTexImage is called.  All pixels
+    // outside the active rectangle are be considered completely transparent for
+    // the purpose of window composition.
+    Rect mCurrentActiveRect;
+
     // mCurrentTransform is the transform identifier for the current texture. It
     // gets set each time updateTexImage is called.
     uint32_t mCurrentTransform;
diff --git a/include/gui/SurfaceTextureClient.h b/include/gui/SurfaceTextureClient.h
index 7fd9be5..c4d4320 100644
--- a/include/gui/SurfaceTextureClient.h
+++ b/include/gui/SurfaceTextureClient.h
@@ -83,6 +83,7 @@
     int dispatchSetUsage(va_list args);
     int dispatchLock(va_list args);
     int dispatchUnlockAndPost(va_list args);
+    int dispatchSetActiveRect(va_list args);
 
 protected:
     virtual int cancelBuffer(ANativeWindowBuffer* buffer);
@@ -106,6 +107,7 @@
     virtual int setUsage(uint32_t reqUsage);
     virtual int lock(ANativeWindow_Buffer* outBuffer, ARect* inOutDirtyBounds);
     virtual int unlockAndPost();
+    virtual int setActiveRect(Rect const* rect);
 
     enum { NUM_BUFFER_SLOTS = BufferQueue::NUM_BUFFER_SLOTS };
     enum { DEFAULT_FORMAT = PIXEL_FORMAT_RGBA_8888 };
@@ -165,6 +167,10 @@
     // buffer that gets queued. It is set by calling setTransform.
     uint32_t mTransform;
 
+    // mActiveRect is the active rectangle that will be used for the next buffer
+    // that gets queued.  It is set by calling setActiveRect.
+    Rect mActiveRect;
+
      // mDefaultWidth is default width of the buffers, regardless of the
      // native_window_set_buffers_dimensions call.
      uint32_t mDefaultWidth;