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diff --git a/core/java/android/transition/PathMotion.java b/core/java/android/transition/PathMotion.java
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+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package android.transition;
+
+import android.content.Context;
+import android.graphics.Path;
+import android.util.AttributeSet;
+
+/**
+ * This base class can be extended to provide motion along a Path to Transitions.
+ *
+ * <p>
+ * Transitions such as {@link android.transition.ChangeBounds} move Views, typically
+ * in a straight path between the start and end positions. Applications that desire to
+ * have these motions move in a curve can change how Views interpolate in two dimensions
+ * by extending PathMotion and implementing {@link #getPath(float, float, float, float)}.
+ * </p>
+ * <p>This may be used in XML as an element inside a transition.</p>
+ * <pre>
+ * {@code
+ * &lt;changeBounds>
+ *     &lt;pathMotion class="my.app.transition.MyPathMotion"/>
+ * &lt;/changeBounds>
+ * }
+ * </pre>
+ */
+public abstract class PathMotion {
+
+    public PathMotion() {}
+
+    public PathMotion(Context context, AttributeSet attrs) {}
+
+    /**
+     * Provide a Path to interpolate between two points <code>(startX, startY)</code> and
+     * <code>(endX, endY)</code>. This allows controlled curved motion along two dimensions.
+     *
+     * @param startX The x coordinate of the starting point.
+     * @param startY The y coordinate of the starting point.
+     * @param endX   The x coordinate of the ending point.
+     * @param endY   The y coordinate of the ending point.
+     * @return A Path along which the points should be interpolated. The returned Path
+     * must start at point <code>(startX, startY)</code>, typically using
+     * {@link android.graphics.Path#moveTo(float, float)} and end at <code>(endX, endY)</code>.
+     */
+    public abstract Path getPath(float startX, float startY, float endX, float endY);
+}