BufferQueue: Add NATIVE_WINDOW_BUFFER_AGE query

Adds a NATIVE_WINDOW_BUFFER_AGE query, which returns the age of the
contents of the most recently dequeued buffer as the number of frames
that have elapsed since it was last queued.

Change-Id: Ib6fd62945cb62d1e60133a65beee510363218a23
(cherry picked from commit 49f810c72df8d1d64128e376757079825c8decd4)

3 files changed, 21 insertions, 1 deletions

diff --git a/include/gui/BufferQueueCore.h b/include/gui/BufferQueueCore.h
index 9a43516..e3624b7 100644
--- a/include/gui/BufferQueueCore.h
+++ b/include/gui/BufferQueueCore.h
@@ -270,6 +270,10 @@ private:
     // mAllowAllocation determines whether dequeueBuffer is allowed to allocate
     // new buffers
     bool mAllowAllocation;
+
+    // mBufferAge tracks the age of the contents of the most recently dequeued
+    // buffer as the number of frames that have elapsed since it was last queued
+    uint64_t mBufferAge;
 }; // class BufferQueueCore
 
 } // namespace android
diff --git a/libs/gui/BufferQueueCore.cpp b/libs/gui/BufferQueueCore.cpp
index bc75ca7..887f2cb 100644
--- a/libs/gui/BufferQueueCore.cpp
+++ b/libs/gui/BufferQueueCore.cpp
@@ -70,7 +70,8 @@ BufferQueueCore::BufferQueueCore(const sp<IGraphicBufferAlloc>& allocator) :
     mTransformHint(0),
     mIsAllocating(false),
     mIsAllocatingCondition(),
-    mAllowAllocation(true)
+    mAllowAllocation(true),
+    mBufferAge(0)
 {
     if (allocator == NULL) {
         sp<ISurfaceComposer> composer(ComposerService::getComposerService());
diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index 86e45c8..b8df436 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -337,10 +337,18 @@ status_t BufferQueueProducer::dequeueBuffer(int *outSlot,
             mSlots[found].mEglDisplay = EGL_NO_DISPLAY;
             mSlots[found].mEglFence = EGL_NO_SYNC_KHR;
             mSlots[found].mFence = Fence::NO_FENCE;
+            mCore->mBufferAge = 0;
 
             returnFlags |= BUFFER_NEEDS_REALLOCATION;
+        } else {
+            // We add 1 because that will be the frame number when this buffer
+            // is queued
+            mCore->mBufferAge =
+                    mCore->mFrameCounter + 1 - mSlots[found].mFrameNumber;
         }
 
+        BQ_LOGV("dequeueBuffer: setting buffer age to %llu", mCore->mBufferAge);
+
         if (CC_UNLIKELY(mSlots[found].mFence == NULL)) {
             BQ_LOGE("dequeueBuffer: about to return a NULL fence - "
                     "slot=%d w=%d h=%d format=%u",
@@ -784,6 +792,13 @@ int BufferQueueProducer::query(int what, int *outValue) {
         case NATIVE_WINDOW_DEFAULT_DATASPACE:
             value = static_cast<int32_t>(mCore->mDefaultBufferDataSpace);
             break;
+        case NATIVE_WINDOW_BUFFER_AGE:
+            if (mCore->mBufferAge > INT32_MAX) {
+                value = 0;
+            } else {
+                value = static_cast<int32_t>(mCore->mBufferAge);
+            }
+            break;
         default:
             return BAD_VALUE;
     }