[Android] Add a native pull-to-refresh overscroll effect

content/public/android/java/src/org/chromium/content/browser/UIResources.java

Index: content/public/android/java/src/org/chromium/content/browser/UIResources.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/UIResources.java b/content/public/android/java/src/org/chromium/content/browser/UIResources.java
new file mode 100644
index 0000000000000000000000000000000000000000..f39f4d628524d799a296d526fde0c14ef6235225
--- /dev/null
+++ b/content/public/android/java/src/org/chromium/content/browser/UIResources.java
@@ -0,0 +1,84 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.content.browser;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.graphics.Bitmap;
+import android.graphics.BitmapFactory;
+
+import org.chromium.base.CalledByNative;
+import org.chromium.base.JNINamespace;
+import org.chromium.content.R;
+import org.chromium.ui.base.SystemUIResourceType;
+
+/**
+ * Helper class for retrieving both system and embedded UI-related resources.
+ */
+@JNINamespace("content")
+class UIResources {
+    private static Bitmap getResourceBitmap(Resources res, int resId, int reqWidth, int reqHeight) {
+        final BitmapFactory.Options options = new BitmapFactory.Options();
+        if (reqWidth > 0 && reqHeight > 0) {
+            options.inJustDecodeBounds = true;
+            BitmapFactory.decodeResource(res, resId, options);
+            options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
+        }
+        options.inJustDecodeBounds = false;
+        options.inPreferredConfig = Bitmap.Config.ARGB_8888;
+        return BitmapFactory.decodeResource(res, resId, options);
+    }
+
+    // http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
+    private static int calculateInSampleSize(
+            BitmapFactory.Options options, int reqWidth, int reqHeight) {
+        // Raw height and width of image
+        final int height = options.outHeight;
+        final int width = options.outWidth;
+        int inSampleSize = 1;
+
+        if (height > reqHeight || width > reqWidth) {
+            // Calculate ratios of height and width to requested height and width
+            final int heightRatio = Math.round((float) height / (float) reqHeight);
+            final int widthRatio = Math.round((float) width / (float) reqWidth);
+
+            // Choose the smallest ratio as inSampleSize value, this will guarantee
+            // a final image with both dimensions larger than or equal to the
+            // requested height and width.
+            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
+        }
+
+        return inSampleSize;
+    }
+
+    @SuppressWarnings("unused")
+    @CalledByNative
+    private static Bitmap getBitmap(
+            Context context, int uiResourceId, int reqWidth, int reqHeight) {
+        Resources res = null;
+        int resId = 0;
+
+        if (uiResourceId == SystemUIResourceType.OVERSCROLL_EDGE) {
+            res = Resources.getSystem();
+            resId = res.getIdentifier("android:drawable/overscroll_edge", null, null);
+        } else if (uiResourceId == SystemUIResourceType.OVERSCROLL_GLOW) {
+            res = Resources.getSystem();
+            resId = res.getIdentifier("android:drawable/overscroll_glow", null, null);
+        } else if (uiResourceId == SystemUIResourceType.OVERSCROLL_REFRESH_IDLE) {
+            res = context.getResources();
+            resId = R.drawable.refresh_gray;
+        } else if (uiResourceId == SystemUIResourceType.OVERSCROLL_REFRESH_ACTIVE) {
+            res = context.getResources();
+            resId = R.drawable.refresh_blue;
+        } else {
+            assert false;
+        }
+
+        if (res == null) return null;
+        if (resId == 0) return null;
+
+        return getResourceBitmap(res, resId, reqWidth, reqHeight);
+    }
+}