OffscreenPreRaster and its plumbings

android_webview/java/src/org/chromium/android_webview/AwSettings.java

Index: android_webview/java/src/org/chromium/android_webview/AwSettings.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwSettings.java b/android_webview/java/src/org/chromium/android_webview/AwSettings.java
index 2d33f5294be0ea5b681e783881b2ac42bc7314ea..9539704681e2955999742d6104360ae3dad211a8 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwSettings.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwSettings.java
@@ -88,6 +88,7 @@ public class AwSettings {
     private boolean mEnableSupportedHardwareAcceleratedFeatures = false;
     private int mMixedContentMode = MIXED_CONTENT_NEVER_ALLOW;
     private boolean mVideoOverlayForEmbeddedVideoEnabled = false;
+    private boolean mOffscreenPreRaster = false;
 
     // Although this bit is stored on AwSettings it is actually controlled via the CookieManager.
     private boolean mAcceptThirdPartyCookies = false;
@@ -1559,6 +1560,40 @@ public class AwSettings {
                 || mMixedContentMode == MIXED_CONTENT_COMPATIBILITY_MODE;
     }
 
+    public boolean getOffscreenPreRaster() {
+        synchronized (mAwSettingsLock) {
+            return mOffscreenPreRaster;
+        }
+    }
+
+    /**
+     * Sets whether this WebView should raster tiles when it is
+     * offscreen but attached to window. Turning this on can avoid
+     * rendering artifacts when animating an offscreen WebView on-screen.
+     * In particular, insertVisualStateCallback requires this mode to function.
+     * Offscreen WebViews in this mode uses more memory. Please follow
+     * these guidelines to limit memory usage:
+     * - Webview size should be not be larger than the device screen size.
+     * - Limit simple mode to a small number of webviews. Use it for
+     *   visible webviews and webviews about to be animated to visible.
+     */
+    public void setOffscreenPreRaster(boolean enabled) {
+        synchronized (mAwSettingsLock) {
+            if (enabled != mOffscreenPreRaster) {
+                mOffscreenPreRaster = enabled;
+                mEventHandler.runOnUiThreadBlockingAndLocked(new Runnable() {

[boliu, 2015/02/20 23:16:07]

Wonder if we can avoid blocking here.

Probably not a big deal either way.

[hush (inactive), 2015/02/20 23:47:21]

Yeah. Not a big deal. I guess you meant to set the flag without posting to the
message queue and just calling the JNI with mAwSettingsLock? The real thing is I
want to post this method to the UI thread, so blocking is inevitable.

[boliu, 2015/02/21 00:03:00]

Not exactly what I meant.

This is post + blocking. In theory, this could post but not block, similar to
maybePostOnUiThread (but should also not post if not on UI thread). Haven't
thought through all the potential implications of this yet..

But then again, this could be argued for all of these settings, not just this
one. Can ask Mikhail about this later I guess :p. Good enough for now.

+                    @Override
+                    public void run() {
+                        if (mNativeAwSettings != 0) {
+                            nativeUpdateOffscreenPreRasterLocked(
+                                    mNativeAwSettings, mOffscreenPreRaster);
+                        }
+                    }
+                });
+            }
+        }
+    }
+
     /**
      * Sets whether to use the video overlay for the embedded video.
      * @param flag whether to enable the video overlay for the embedded video.
@@ -1671,4 +1706,7 @@ public class AwSettings {
     private native void nativeUpdateFormDataPreferencesLocked(long nativeAwSettings);
 
     private native void nativeUpdateRendererPreferencesLocked(long nativeAwSettings);
+
+    private native void nativeUpdateOffscreenPreRasterLocked(
+            long nativeAwSettings, boolean enabled);
 }