diff --git a/include/utils/RefBase.h b/include/utils/RefBase.h
index c24c0db..f8d96cf 100644
--- a/include/utils/RefBase.h
+++ b/include/utils/RefBase.h
@@ -18,7 +18,6 @@
 #define ANDROID_REF_BASE_H
 
 #include <cutils/atomic.h>
-#include <utils/TextOutput.h>
 
 #include <stdint.h>
 #include <sys/types.h>
@@ -27,6 +26,10 @@
 // ---------------------------------------------------------------------------
 namespace android {
 
+class TextOutput;
+TextOutput& printStrongPointer(TextOutput& to, const void* val);
+TextOutput& printWeakPointer(TextOutput& to, const void* val);
+
 template<typename T> class wp;
 
 // ---------------------------------------------------------------------------
@@ -427,8 +430,7 @@
 template <typename T>
 inline TextOutput& operator<<(TextOutput& to, const sp<T>& val)
 {
-    to << "sp<>(" << val.get() << ")";
-    return to;
+   return printStrongPointer(to, val.get());
 }
 
 // ---------------------------------------------------------------------------
@@ -585,8 +587,7 @@
 template <typename T>
 inline TextOutput& operator<<(TextOutput& to, const wp<T>& val)
 {
-    to << "wp<>(" << val.unsafe_get() << ")";
-    return to;
+    return printWeakPointer(to, val.unsafe_get());
 }
 
 }; // namespace android
diff --git a/libs/utils/RefBase.cpp b/libs/utils/RefBase.cpp
index 0bd1af4..f934eec 100644
--- a/libs/utils/RefBase.cpp
+++ b/libs/utils/RefBase.cpp
@@ -23,6 +23,7 @@
 #include <utils/KeyedVector.h>
 #include <utils/Log.h>
 #include <utils/threads.h>
+#include <utils/TextOutput.h>
 
 #include <stdlib.h>
 #include <stdio.h>
@@ -530,5 +531,20 @@
 void RefBase::onLastWeakRef(const void* /*id*/)
 {
 }
-        
+
+// ---------------------------------------------------------------------------
+
+TextOutput& printStrongPointer(TextOutput& to, const void* val)
+{
+    to << "sp<>(" << val << ")";
+    return to;
+}
+
+TextOutput& printWeakPointer(TextOutput& to, const void* val)
+{
+    to << "wp<>(" << val << ")";
+    return to;
+}
+
+
 }; // namespace android
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 0f7d639..57af001 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -341,6 +341,45 @@
     drawWithOpenGL(clip, tex);
 }
 
+// As documented in libhardware header, formats in the range
+// 0x100 - 0x1FF are specific to the HAL implementation, and
+// are known to have no alpha channel
+// TODO: move definition for device-specific range into
+// hardware.h, instead of using hard-coded values here.
+#define HARDWARE_IS_DEVICE_FORMAT(f) ((f) >= 0x100 && (f) <= 0x1FF)
+
+bool Layer::needsBlending(const sp<GraphicBuffer>& buffer) const
+{
+    // If buffers where set with eOpaque flag, all buffers are known to
+    // be opaque without having to check their actual format
+    if (mNeedsBlending && buffer != NULL) {
+        PixelFormat format = buffer->getPixelFormat();
+
+        if (HARDWARE_IS_DEVICE_FORMAT(format)) {
+            return false;
+        }
+
+        PixelFormatInfo info;
+        status_t err = getPixelFormatInfo(format, &info);
+        if (!err && info.h_alpha <= info.l_alpha) {
+            return false;
+        }
+    }
+
+    // Return opacity as determined from flags and format options
+    // passed to setBuffers()
+    return mNeedsBlending;
+}
+
+bool Layer::needsBlending() const
+{
+    if (mBufferManager.hasActiveBuffer()) {
+        return needsBlending(mBufferManager.getActiveBuffer());
+    }
+
+    return mNeedsBlending;
+}
+
 bool Layer::needsFiltering() const
 {
     if (!(mFlags & DisplayHardware::SLOW_CONFIG)) {
@@ -588,6 +627,9 @@
     // we retired a buffer, which becomes the new front buffer
 
     const bool noActiveBuffer = !mBufferManager.hasActiveBuffer();
+    const bool activeBlending =
+            noActiveBuffer ? true : needsBlending(mBufferManager.getActiveBuffer());
+
     if (mBufferManager.setActiveBufferIndex(buf) < NO_ERROR) {
         LOGE("retireAndLock() buffer index (%d) out of range", int(buf));
         mPostedDirtyRegion.clear();
@@ -602,6 +644,12 @@
 
     sp<GraphicBuffer> newFrontBuffer(getBuffer(buf));
     if (newFrontBuffer != NULL) {
+        if (!noActiveBuffer && activeBlending != needsBlending(newFrontBuffer)) {
+            // new buffer has different opacity than previous active buffer, need
+            // to recompute visible regions accordingly
+            recomputeVisibleRegions = true;
+        }
+
         // get the dirty region
         // compute the posted region
         const Region dirty(lcblk->getDirtyRegion(buf));
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 2b38414..bccc900 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -75,7 +75,8 @@
     virtual uint32_t doTransaction(uint32_t transactionFlags);
     virtual void lockPageFlip(bool& recomputeVisibleRegions);
     virtual void unlockPageFlip(const Transform& planeTransform, Region& outDirtyRegion);
-    virtual bool needsBlending() const      { return mNeedsBlending; }
+    virtual bool needsBlending(const sp<GraphicBuffer>& buffer) const;
+    virtual bool needsBlending() const;
     virtual bool needsDithering() const     { return mNeedsDithering; }
     virtual bool needsFiltering() const;
     virtual bool isSecure() const           { return mSecure; }