Take advantage of EGL_BUFFER_PRESERVED on IMG.

The IMG architecture does not support the EGL_SWAP_BEHAVIOR_PRESERVED_BIT
in EGL configurations. This bit is used only to be able to change the
EGL_SWAP_BEHAVIOR, which matters when the default behavior is not the
one we want. However on IMG, the default swap behavior is the one we
desire.

Change-Id: Iff5980c97df9e41bc837e424baf83b8eadbb7161

3 files changed, 57 insertions, 3 deletions

diff --git a/core/java/android/view/GLES20Canvas.java b/core/java/android/view/GLES20Canvas.java
index 2b79a76..d5cad96 100644
--- a/core/java/android/view/GLES20Canvas.java
+++ b/core/java/android/view/GLES20Canvas.java
@@ -201,6 +201,14 @@ class GLES20Canvas extends HardwareCanvas {
     private static native void nSetViewport(int renderer, int width, int height);
 
     /**
+     * Preserves the back buffer of the current surface after a buffer swap.
+     * Calling this method sets the EGL_SWAP_BEHAVIOR attribute of the current
+     * surface to EGL_BUFFER_PRESERVED. Calling this method requires an EGL
+     * config that supports EGL_SWAP_BEHAVIOR_PRESERVED_BIT.
+     * 
+     * @return True if the swap behavior was successfully changed,
+     *         false otherwise.
+     * 
      * @hide
      */
     public static boolean preserveBackBuffer() {
@@ -208,6 +216,21 @@ class GLES20Canvas extends HardwareCanvas {
     }
 
     private static native boolean nPreserveBackBuffer();    
+
+    /**
+     * Indicates whether the current surface preserves its back buffer
+     * after a buffer swap.
+     * 
+     * @return True, if the surface's EGL_SWAP_BEHAVIOR is EGL_BUFFER_PRESERVED,
+     *         false otherwise
+     *         
+     * @hide
+     */
+    public static boolean isBackBufferPreserved() {
+        return nIsBackBufferPreserved();
+    }
+
+    private static native boolean nIsBackBufferPreserved();    
     
     @Override
     void onPreDraw(Rect dirty) {
diff --git a/core/java/android/view/HardwareRenderer.java b/core/java/android/view/HardwareRenderer.java
index 61a24a0..2611ec0 100644
--- a/core/java/android/view/HardwareRenderer.java
+++ b/core/java/android/view/HardwareRenderer.java
@@ -311,6 +311,7 @@ public abstract class HardwareRenderer {
         Paint mDebugPaint;
 
         boolean mDirtyRegions;
+        final boolean mDirtyRegionsRequested;
 
         final int mGlVersion;
         final boolean mTranslucent;
@@ -325,6 +326,7 @@ public abstract class HardwareRenderer {
             final String dirtyProperty = SystemProperties.get(RENDER_DIRTY_REGIONS_PROPERTY, "true");
             //noinspection PointlessBooleanExpression,ConstantConditions
             mDirtyRegions = RENDER_DIRTY_REGIONS && "true".equalsIgnoreCase(dirtyProperty);
+            mDirtyRegionsRequested = mDirtyRegions;
         }
 
         /**
@@ -545,11 +547,21 @@ public abstract class HardwareRenderer {
                 throw new Surface.OutOfResourcesException("eglMakeCurrent failed "
                         + getEGLErrorString(sEgl.eglGetError()));
             }
-            
+
+            // If mDirtyRegions is set, this means we have an EGL configuration
+            // with EGL_SWAP_BEHAVIOR_PRESERVED_BIT set
             if (mDirtyRegions) {
                 if (!GLES20Canvas.preserveBackBuffer()) {
                     Log.w(LOG_TAG, "Backbuffer cannot be preserved");
                 }
+            } else if (mDirtyRegionsRequested) {
+                // If mDirtyRegions is not set, our EGL configuration does not
+                // have EGL_SWAP_BEHAVIOR_PRESERVED_BIT; however, the default
+                // swap behavior might be EGL_BUFFER_PRESERVED, which means we
+                // want to set mDirtyRegions. We try to do this only if dirty
+                // regions were initially requested as part of the device
+                // configuration (see RENDER_DIRTY_REGIONS)
+                mDirtyRegions = GLES20Canvas.isBackBufferPreserved();
             }
 
             return sEglContext.getGL();
diff --git a/core/jni/android_view_GLES20Canvas.cpp b/core/jni/android_view_GLES20Canvas.cpp
index e2832ed..31988f7 100644
--- a/core/jni/android_view_GLES20Canvas.cpp
+++ b/core/jni/android_view_GLES20Canvas.cpp
@@ -91,11 +91,29 @@ static jboolean android_view_GLES20Canvas_preserveBackBuffer(JNIEnv* env, jobjec
     eglSurfaceAttrib(display, surface, EGL_SWAP_BEHAVIOR, EGL_BUFFER_PRESERVED);
 
     EGLint error = eglGetError();
-    RENDERER_LOGD("Could not enable buffer preserved swap behavior (%x)", error);
+    if (error != EGL_SUCCESS) {
+        RENDERER_LOGD("Could not enable buffer preserved swap behavior (%x)", error);
+    }
 
     return error == EGL_SUCCESS;
 }
 
+static jboolean android_view_GLES20Canvas_isBackBufferPreserved(JNIEnv* env, jobject clazz) {
+    EGLDisplay display = eglGetCurrentDisplay();
+    EGLSurface surface = eglGetCurrentSurface(EGL_DRAW);
+    EGLint value;
+
+    eglGetError();
+    eglQuerySurface(display, surface, EGL_SWAP_BEHAVIOR, &value);
+
+    EGLint error = eglGetError();
+    if (error != EGL_SUCCESS) {
+        RENDERER_LOGD("Could not query buffer preserved swap behavior (%x)", error);
+    }
+
+    return error == EGL_SUCCESS && value == EGL_BUFFER_PRESERVED;
+}
+
 // ----------------------------------------------------------------------------
 // Constructors
 // ----------------------------------------------------------------------------
@@ -676,7 +694,8 @@ static JNINativeMethod gMethods[] = {
     { "nIsAvailable",       "()Z",             (void*) android_view_GLES20Canvas_isAvailable },
 
 #ifdef USE_OPENGL_RENDERER
-    { "nPreserveBackBuffer", "()Z",            (void*) android_view_GLES20Canvas_preserveBackBuffer },
+    { "nIsBackBufferPreserved", "()Z",         (void*) android_view_GLES20Canvas_isBackBufferPreserved },
+    { "nPreserveBackBuffer",    "()Z",         (void*) android_view_GLES20Canvas_preserveBackBuffer },
 
     { "nCreateRenderer",    "()I",             (void*) android_view_GLES20Canvas_createRenderer },
     { "nDestroyRenderer",   "(I)V",            (void*) android_view_GLES20Canvas_destroyRenderer },