From 140755f2cfe6a39f643ab0a9ca2d81b0ed470ae7 Mon Sep 17 00:00:00 2001
From: Po Lu
Date: Thu, 13 Jul 2023 12:05:50 +0800
Subject: Disable hardware acceleration on Android

It serves no purpose and causes tearing.  Uploading the bitmap
to the GPU takes about as long as it does to incrementally
update the surface in software.

* java/AndroidManifest.xml.in: Disable hardware acceleration.
* java/org/gnu/emacs/EmacsActivity.java (EmacsActivity): Make
lastClosedMenu static.
* java/org/gnu/emacs/EmacsDialog.java (toAlertDialog): Enable
hardware acceleration within alert dialogs.
* java/org/gnu/emacs/EmacsSurfaceView.java (onDraw): Describe
why hardware acceleration is disabled.
* java/org/gnu/emacs/EmacsWindow.java (run): Remove redundant
call.
---
 java/AndroidManifest.xml.in              |  5 +++++
 java/org/gnu/emacs/EmacsActivity.java    |  2 +-
 java/org/gnu/emacs/EmacsDialog.java      | 14 +++++++++++++-
 java/org/gnu/emacs/EmacsSurfaceView.java | 20 +++++++++++++++++++-
 java/org/gnu/emacs/EmacsWindow.java      |  2 +-
 5 files changed, 39 insertions(+), 4 deletions(-)

(limited to 'java')

diff --git a/java/AndroidManifest.xml.in b/java/AndroidManifest.xml.in
index e79fb4e46e7..f2aede7369c 100644
--- a/java/AndroidManifest.xml.in
+++ b/java/AndroidManifest.xml.in
@@ -77,10 +77,14 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
 	       @ANDROID_SHARED_USER_ID@
 	       android:extractNativeLibs="true">
 
+    <!-- See EmacsSurfaceView.onDraw for why hardware acceleration is
+         disabled.  -->
+
     <activity android:name="org.gnu.emacs.EmacsActivity"
 	      android:launchMode="singleInstance"
 	      android:windowSoftInputMode="adjustResize"
 	      android:exported="true"
+	      android:hardwareAccelerated="false"
 	      android:configChanges="orientation|screenSize|screenLayout|keyboardHidden">
       <intent-filter>
         <action android:name="android.intent.action.MAIN" />
@@ -173,6 +177,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
     <activity android:name="org.gnu.emacs.EmacsMultitaskActivity"
 	      android:windowSoftInputMode="adjustResize"
 	      android:exported="true"
+	      android:hardwareAccelerated="false"
 	      android:configChanges="orientation|screenSize|screenLayout|keyboardHidden"/>
 
     <activity android:autoRemoveFromRecents="true"
diff --git a/java/org/gnu/emacs/EmacsActivity.java b/java/org/gnu/emacs/EmacsActivity.java
index fa9bff39bb0..d7b51388929 100644
--- a/java/org/gnu/emacs/EmacsActivity.java
+++ b/java/org/gnu/emacs/EmacsActivity.java
@@ -70,7 +70,7 @@ public class EmacsActivity extends Activity
   private boolean isFullscreen;
 
   /* The last context menu to be closed.  */
-  private Menu lastClosedMenu;
+  private static Menu lastClosedMenu;
 
   static
   {
diff --git a/java/org/gnu/emacs/EmacsDialog.java b/java/org/gnu/emacs/EmacsDialog.java
index 5f48a9a5f9f..42455ed78f8 100644
--- a/java/org/gnu/emacs/EmacsDialog.java
+++ b/java/org/gnu/emacs/EmacsDialog.java
@@ -152,7 +152,7 @@ public final class EmacsDialog implements DialogInterface.OnDismissListener
   toAlertDialog (Context context)
   {
     AlertDialog dialog;
-    int size, styleId;
+    int size, styleId, flag;
     int[] attrs;
     EmacsButton button;
     EmacsDialogButtonLayout layout;
@@ -160,6 +160,7 @@ public final class EmacsDialog implements DialogInterface.OnDismissListener
     ViewGroup.LayoutParams layoutParams;
     Theme theme;
     TypedArray attributes;
+    Window window;
 
     size = buttons.size ();
     styleId = -1;
@@ -273,6 +274,17 @@ public final class EmacsDialog implements DialogInterface.OnDismissListener
 	  }
       }
 
+    /* Make sure the dialog is hardware accelerated.  Hardware
+       acceleration is disabled for dialogs by default, because they
+       aren't enabled in EmacsActivity either.  */
+
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
+      {
+	flag = WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
+	window = dialog.getWindow ();
+	window.addFlags (flag);
+      }
+
     return dialog;
   }
 
diff --git a/java/org/gnu/emacs/EmacsSurfaceView.java b/java/org/gnu/emacs/EmacsSurfaceView.java
index 3f62af4ab99..54fe70e1634 100644
--- a/java/org/gnu/emacs/EmacsSurfaceView.java
+++ b/java/org/gnu/emacs/EmacsSurfaceView.java
@@ -176,7 +176,25 @@ public final class EmacsSurfaceView extends View
   onDraw (Canvas canvas)
   {
     /* Paint the view's bitmap; the bitmap might be recycled right
-       now.  */
+       now.
+
+       Hardware acceleration is disabled in AndroidManifest.xml to
+       prevent Android from uploading the front buffer to the GPU from
+       a separate thread.  This is important for two reasons: first,
+       the GPU command queue uses a massive amount of memory (dozens
+       of MiB) to upload bitmaps to the GPU, regardless of how much of
+       the bitmap has actually changed.
+
+       Secondly, asynchronous texturization leads to race conditions
+       when a buffer swap occurs before the front buffer is fully
+       uploaded to the GPU.  Normally, only slight and tolerable
+       tearing should result from this behavior, but Android does not
+       properly interlock the ``generation ID'' used to avoid
+       texturizing unchanged bitmaps with the bitmap contents,
+       consequentially leading to textures in an incomplete state
+       remaining in use to the GPU if a buffer swap happens between
+       the image data being uploaded and the ``generation ID'' being
+       read.  */
 
     if (frontBuffer != null)
       canvas.drawBitmap (frontBuffer, 0f, 0f, uiThreadPaint);
diff --git a/java/org/gnu/emacs/EmacsWindow.java b/java/org/gnu/emacs/EmacsWindow.java
index 5e45275631b..0e96a8382d0 100644
--- a/java/org/gnu/emacs/EmacsWindow.java
+++ b/java/org/gnu/emacs/EmacsWindow.java
@@ -1377,7 +1377,7 @@ public final class EmacsWindow extends EmacsHandleObject
 
 	  if (tem != null)
 	    {
-	      activity = (EmacsActivity) getAttachedConsumer ();
+	      activity = (EmacsActivity) tem;
 	      activity.syncFullscreenWith (EmacsWindow.this);
 	    }
 	}
-- 
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