Pay attention to buffer timestamps

When acquiring a buffer, SurfaceFlinger now computes the expected
presentation time and passes it to the BufferQueue acquireBuffer()
method.  If it's not yet time to display the buffer, acquireBuffer()
returns PRESENT_LATER instead of a buffer.

The current implementation of the expected-present-time computation
uses approximations and guesswork.

Bug 7900302

Change-Id: If9345611c5983a11a811935aaf27d6388a5036f1

4 files changed, 14 insertions, 5 deletions

diff --git a/include/gui/BufferItemConsumer.h b/include/gui/BufferItemConsumer.h
index 98b450c..5bf9acb 100644
--- a/include/gui/BufferItemConsumer.h
+++ b/include/gui/BufferItemConsumer.h
@@ -71,7 +71,8 @@ class BufferItemConsumer: public ConsumerBase
     //
     // If waitForFence is true, and the acquired BufferItem has a valid fence object,
     // acquireBuffer will wait on the fence with no timeout before returning.
-    status_t acquireBuffer(BufferItem *item, bool waitForFence = true);
+    status_t acquireBuffer(BufferItem *item, nsecs_t presentWhen,
+        bool waitForFence = true);
 
     // Returns an acquired buffer to the queue, allowing it to be reused. Since
     // only a fixed number of buffers may be acquired at a time, old buffers
diff --git a/include/gui/BufferQueue.h b/include/gui/BufferQueue.h
index 766fa0f..0143be3 100644
--- a/include/gui/BufferQueue.h
+++ b/include/gui/BufferQueue.h
@@ -39,7 +39,7 @@ public:
     enum { NUM_BUFFER_SLOTS = 32 };
     enum { NO_CONNECTED_API = 0 };
     enum { INVALID_BUFFER_SLOT = -1 };
-    enum { STALE_BUFFER_SLOT = 1, NO_BUFFER_AVAILABLE };
+    enum { STALE_BUFFER_SLOT = 1, NO_BUFFER_AVAILABLE, PRESENT_LATER };
 
     // When in async mode we reserve two slots in order to guarantee that the
     // producer and consumer can run asynchronously.
@@ -284,7 +284,13 @@ public:
     // acquired then the BufferItem::mGraphicBuffer field of buffer is set to
     // NULL and it is assumed that the consumer still holds a reference to the
     // buffer.
-    status_t acquireBuffer(BufferItem *buffer);
+    //
+    // If presentWhen is nonzero, it indicates the time when the buffer will
+    // be displayed on screen.  If the buffer's timestamp is farther in the
+    // future, the buffer won't be acquired, and PRESENT_LATER will be
+    // returned.  The presentation time is in nanoseconds, and the time base
+    // is CLOCK_MONOTONIC.
+    status_t acquireBuffer(BufferItem *buffer, nsecs_t presentWhen);
 
     // releaseBuffer releases a buffer slot from the consumer back to the
     // BufferQueue.  This may be done while the buffer's contents are still
diff --git a/include/gui/ConsumerBase.h b/include/gui/ConsumerBase.h
index 1d51bc9..42b84cc 100644
--- a/include/gui/ConsumerBase.h
+++ b/include/gui/ConsumerBase.h
@@ -152,7 +152,8 @@ protected:
     // initialization that must take place the first time a buffer is assigned
     // to a slot.  If it is overridden the derived class's implementation must
     // call ConsumerBase::acquireBufferLocked.
-    virtual status_t acquireBufferLocked(BufferQueue::BufferItem *item);
+    virtual status_t acquireBufferLocked(BufferQueue::BufferItem *item,
+        nsecs_t presentWhen);
 
     // releaseBufferLocked relinquishes control over a buffer, returning that
     // control to the BufferQueue.
diff --git a/include/gui/GLConsumer.h b/include/gui/GLConsumer.h
index 031684e..fbc8840 100644
--- a/include/gui/GLConsumer.h
+++ b/include/gui/GLConsumer.h
@@ -237,7 +237,8 @@ protected:
 
     // acquireBufferLocked overrides the ConsumerBase method to update the
     // mEglSlots array in addition to the ConsumerBase behavior.
-    virtual status_t acquireBufferLocked(BufferQueue::BufferItem *item);
+    virtual status_t acquireBufferLocked(BufferQueue::BufferItem *item,
+        nsecs_t presentWhen);
 
     // releaseBufferLocked overrides the ConsumerBase method to update the
     // mEglSlots array in addition to the ConsumerBase.