[Android WebView] Implement the capture picture API.

android_webview/java/src/org/chromium/android_webview/AwContents.java

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 3d51cb74bf595552e9751b2ad554db3e24146aa4..75c34fcf8579cad15398f703365b379fd1301d45 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -8,6 +8,7 @@ import android.content.res.Configuration;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
 import android.graphics.Color;
+import android.graphics.Picture;
 import android.graphics.Rect;
 import android.net.http.SslCertificate;
 import android.os.AsyncTask;
@@ -39,6 +40,7 @@ import org.chromium.net.X509Util;
 import org.chromium.ui.gfx.NativeWindow;
 
 import java.io.File;
+import java.lang.ref.SoftReference;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.security.KeyStoreException;
@@ -104,6 +106,9 @@ public class AwContents {
     // Must call nativeUpdateLastHitTestData first to update this before use.
     private final HitTestData mPossiblyStaleHitTestData;
 
+    // Cached bitmap used for rasterizing Pictures.
+    private SoftReference<Bitmap> mPictureBitmapCache;
+
     private static final class DestroyRunnable implements Runnable {
         private int mNativeAwContents;
         private DestroyRunnable(int nativeAwContents) {
@@ -402,6 +407,19 @@ public class AwContents {
         mLayoutSizer.onMeasure(widthMeasureSpec, heightMeasureSpec);
     }
 
+    public Picture capturePicture() {
+        return nativeCapturePicture(mNativeAwContents);
+    }
+
+    /**
+     * Enable the OnNewPicture callback.
+     * @param enabled Flag to enable the callback.
+     * @param invalidationOnly Flag to call back only on invalidation without providing a picture.
+     */
+    public void enableOnNewPicture(boolean enabled, boolean invalidationOnly) {
+        nativeEnableOnNewPicture(mNativeAwContents, enabled, invalidationOnly);
+    }
+
     public int findAllSync(String searchString) {
         if (mNativeAwContents == 0) return 0;
         return nativeFindAllSync(mNativeAwContents, searchString);
@@ -907,6 +925,11 @@ public class AwContents {
         mContentsClient.onFindResultReceived(activeMatchOrdinal, numberOfMatches, isDoneCounting);
     }
 
+    @CalledByNative
+    public void onNewPicture(Picture picture) {
+        mContentsClient.onNewPicture(picture);
+    }
+
     // Called as a result of nativeUpdateLastHitTestData.
     @CalledByNative
     private void updateHitTestData(
@@ -979,6 +1002,30 @@ public class AwContents {
         return null;
     }
 
+    /**
+     * Rasterizes the latest available picture into a bitmap and draws it into a new Picture.
+     * This approach has performance issues and should only be used as a fallback mechanism.
+     */
+    @CalledByNative
+    private Picture rasterizeIntoPicture(int nativePicture, int width, int height) {
+        if (mPictureBitmapCache == null || mPictureBitmapCache.get() == null ||
+                mPictureBitmapCache.get().getWidth() != width ||
+                mPictureBitmapCache.get().getHeight() != height) {

[joth, 2013/01/14 23:20:57]

nit: this is technically racy, as the ref maybe GCed between the 2nd & third
clause.
IMO cleanest pattern is:

/// avoid the initial null check...
SoftReference<Bitmap> mPictureBitmapCache = new SoftReference<Bitmap>();  
...


Bitmap bitmap = mPictureBitmapCache.get();
if (bitmap == null || bitmap.width != w || bitmap.h != h) {
  bitmap = Bitmap.create(...)
  mPictureBitmapCache.set(bitmap);
}
...

[Leandro Graciá Gil, 2013/01/15 18:49:23]

Two issues with your approach:
1. SoftReference<> doesn't have a default constructor, so we need to create it
with the actual reference to keep.
2. SoftReference<> doesn't have a set method (goto 1).

I'll be fixing the racy .get().

+            mPictureBitmapCache = new SoftReference<Bitmap>(
+                    Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888));
+            mPictureBitmapCache.get().eraseColor(Color.BLACK);
+        }
+
+        Bitmap bitmap = mPictureBitmapCache.get();
+        if (!nativeRasterizePicture(bitmap, nativePicture)) return null;
+
+        Picture picture = new Picture();
+        Canvas recordingCanvas = picture.beginRecording(width, height);
+        recordingCanvas.drawBitmap(bitmap, 0, 0, null);
+        picture.endRecording();
+        return picture;
+    }
+
     @CalledByNative
     private void handleJsAlert(String url, String message, JsResultReceiver receiver) {
         mContentsClient.handleJsAlert(url, message, receiver);
@@ -1008,6 +1055,7 @@ public class AwContents {
     private static native void nativeDestroy(int nativeAwContents);
     private static native void nativeSetAwDrawSWFunctionTable(int functionTablePointer);
     private static native int nativeGetAwDrawGLFunction();
+    private static native boolean nativeRasterizePicture(Bitmap bitmap, int nativePicture);
 
     private native int nativeGetWebContents(int nativeAwContents);
     private native void nativeDidInitializeContentViewCore(int nativeAwContents,
@@ -1047,4 +1095,8 @@ public class AwContents {
     private native int nativeReleasePopupWebContents(int nativeAwContents);
     private native void nativeSetWebContents(int nativeAwContents, int nativeNewWebContents);
     private native void nativeFocusFirstNode(int nativeAwContents);
+
+    private native Picture nativeCapturePicture(int nativeAwContents);
+    private native void nativeEnableOnNewPicture(int nativeAwContents, boolean enabled,
+            boolean invalidationOnly);
 }