Fixed a few issues with blast sync with SurfaceView

If SurfaceView changed and needs to update its SurfaceControl, it will
append its changes to the main window's blast sync transaction. This is
to ensure it can synchronize with the main window.

However, if SV changes, but the main window doesn't need to submit a new
frame, the logic to synchronize doesn't work. This changes fixes a few
issues

1. Make sure to force a full redraw when
mNextDrawUseBLASTSyncTransaction. This is to ensure we get the proper
callbacks even if there's no new content to draw

2. Clear nextTransaction in BBQ when a frameCompleteCallback is invoked.
In most cases the transaction in BBQ is already cleared since the
frameCompleteCallback is called after a frame is latched and BBQ will
clear the nextTransaction that was set. This is needed when hwui won't
draw a new frame since there's nothing new to draw. In that case, we
will get an immediate frameCompleteCallback without invoking the
processNextBuffer. If VRI doesn't clear the transaction, BBQ will try to
use the stale transaction when a new frame does come in

Test: blast sync in SV enabled doesn't freeze YT
Bug: 172579592
Change-Id: Idca7accdf094dbb4585897e4e884c1147b1a2cd0

2 files changed, 22 insertions, 3 deletions

diff --git a/core/java/android/view/ViewRootImpl.java b/core/java/android/view/ViewRootImpl.java
index 9d24dff13175..ffb43b774199 100644
--- a/core/java/android/view/ViewRootImpl.java
+++ b/core/java/android/view/ViewRootImpl.java
@@ -3912,7 +3912,8 @@ public final class ViewRootImpl implements ViewParent,
             return;
         }
 
-        final boolean fullRedrawNeeded = mFullRedrawNeeded || mReportNextDraw;
+        final boolean fullRedrawNeeded =
+                mFullRedrawNeeded || mReportNextDraw || mNextDrawUseBLASTSyncTransaction;
         mFullRedrawNeeded = false;
 
         mIsDrawing = true;
@@ -9921,6 +9922,18 @@ public final class ViewRootImpl implements ViewParent,
             } else {
                 t.merge(mRtBLASTSyncTransaction);
             }
+
+            // There's potential for the frame callback to get called even if nothing was drawn.
+            // When that occurs, we remove the transaction sent to BBQ since the draw we were
+            // waiting on will not happen. We can apply the transaction here but it will not contain
+            // a buffer since nothing new was drawn.
+            //
+            // This is mainly for the case when the SurfaceView has changed and wants to synchronize
+            // with the main window. If the main window doesn't need to draw anything, we can just
+            // apply the transaction without the new buffer from the main window.
+            if (mBlastBufferQueue != null) {
+                mBlastBufferQueue.setNextTransaction(null);
+            }
         }
     }
 
diff --git a/graphics/java/android/graphics/BLASTBufferQueue.java b/graphics/java/android/graphics/BLASTBufferQueue.java
index 94bfdc9dbad6..4309ab24cc22 100644
--- a/graphics/java/android/graphics/BLASTBufferQueue.java
+++ b/graphics/java/android/graphics/BLASTBufferQueue.java
@@ -16,6 +16,7 @@
 
 package android.graphics;
 
+import android.annotation.Nullable;
 import android.view.Surface;
 import android.view.SurfaceControl;
 
@@ -60,8 +61,13 @@ public final class BLASTBufferQueue {
         return nativeGetSurface(mNativeObject, true /* includeSurfaceControlHandle */);
     }
 
-    public void setNextTransaction(SurfaceControl.Transaction t) {
-        nativeSetNextTransaction(mNativeObject, t.mNativeObject);
+    /**
+     * Send the transaction to BBQ so the next frame can be added and not applied immediately.
+     * This gives the caller a chance to apply the transaction when it's ready.
+     * @param t The transaction to add the frame to. This can be null to clear the transaction.
+     */
+    public void setNextTransaction(@Nullable SurfaceControl.Transaction t) {
+        nativeSetNextTransaction(mNativeObject, t == null ? 0 : t.mNativeObject);
     }
 
     public void update(SurfaceControl sc, int width, int height) {