Skip eglSwapBuffers() call when we do not draw to GL

The fix is to track when we issue GL drawing commands, and to skip the
call to eglSwapBuffers() when a DisplayList does not result in
any actual rendering calls to GL.

Issue #6364143 QuickMuni list items and buttons flicker instead of fade

Change-Id: I60a02c61a58c32d92481a1e814b4c8a49c6a37a3

Author: chethaase

core/java/android/view/DisplayList.java

@@ -61,6 +61,13 @@ public abstract class DisplayList {
      */
     public static final int STATUS_INVOKE = 0x2;
 
+    /**
+     * Indicates that the display list performed GL drawing operations.
+     *
+     * @see HardwareCanvas#drawDisplayList(DisplayList, android.graphics.Rect, int)
+     */
+    public static final int STATUS_DREW = 0x4;
+
     /**
      * Starts recording the display list. All operations performed on the
      * returned canvas are recorded and stored in this display list.

core/java/android/view/HardwareRenderer.java

@@ -1102,6 +1102,7 @@ boolean draw(View view, View.AttachInfo attachInfo, HardwareDrawCallbacks callba
 
                     onPreDraw(dirty);
 
+                    int status = DisplayList.STATUS_DONE;
                     int saveCount = canvas.save();
                     callbacks.onHardwarePreDraw(canvas);
 
@@ -1135,7 +1136,7 @@ boolean draw(View view, View.AttachInfo attachInfo, HardwareDrawCallbacks callba
                                 drawDisplayListStartTime = System.nanoTime();
                             }
 
-                            int status = canvas.drawDisplayList(displayList, mRedrawClip,
+                            status = canvas.drawDisplayList(displayList, mRedrawClip,
                                     DisplayList.FLAG_CLIP_CHILDREN);
 
                             if (mProfileEnabled) {
@@ -1171,22 +1172,25 @@ boolean draw(View view, View.AttachInfo attachInfo, HardwareDrawCallbacks callba
                     onPostDraw();
 
                     attachInfo.mIgnoreDirtyState = false;
+                    
+                    if ((status & DisplayList.STATUS_DREW) == DisplayList.STATUS_DREW) {
 
-                    long eglSwapBuffersStartTime = 0;
-                    if (mProfileEnabled) {
-                        eglSwapBuffersStartTime = System.nanoTime();
-                    }
-
-                    sEgl.eglSwapBuffers(sEglDisplay, mEglSurface);
-
-                    if (mProfileEnabled) {
-                        long now = System.nanoTime();
-                        float total = (now - eglSwapBuffersStartTime) * 0.000001f;
-                        mProfileData[mProfileCurrentFrame + 2] = total;
+                        long eglSwapBuffersStartTime = 0;
+                        if (mProfileEnabled) {
+                            eglSwapBuffersStartTime = System.nanoTime();
+                        }
+    
+                        sEgl.eglSwapBuffers(sEglDisplay, mEglSurface);
+    
+                        if (mProfileEnabled) {
+                            long now = System.nanoTime();
+                            float total = (now - eglSwapBuffersStartTime) * 0.000001f;
+                            mProfileData[mProfileCurrentFrame + 2] = total;
+                        }
+    
+                        checkEglErrors();
                     }
 
-                    checkEglErrors();
-
                     return dirty == null;
                 }
             }

include/private/hwui/DrawGlInfo.h

@@ -72,7 +72,14 @@ struct DrawGlInfo {
         // The functor needs to be invoked again but will
         // not redraw. Only the functor is invoked again
         // (unless another functor requests a redraw.)
-        kStatusInvoke = 0x2
+        kStatusInvoke = 0x2,
+        // DisplayList actually issued GL drawing commands.
+        // This is used to signal the HardwareRenderer that the
+        // buffers should be flipped - otherwise, there were no
+        // changes to the buffer, so no need to flip. Some hardware
+        // has issues with stale buffer contents when no GL
+        // commands are issued.
+        kStatusDrew = 0x4
     };
 }; // struct DrawGlInfo