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diff --git a/services/java/com/android/server/power/RampAnimator.java b/services/java/com/android/server/power/RampAnimator.java
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+++ b/services/java/com/android/server/power/RampAnimator.java
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+/*
+ * Copyright (C) 2012 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 com.android.server.power;
+
+import android.animation.ValueAnimator;
+import android.util.IntProperty;
+import android.view.Choreographer;
+
+/**
+ * A custom animator that progressively updates a property value at
+ * a given variable rate until it reaches a particular target value.
+ */
+final class RampAnimator<T> {
+    private final T mObject;
+    private final IntProperty<T> mProperty;
+    private final Choreographer mChoreographer;
+
+    private int mCurrentValue;
+    private int mTargetValue;
+    private int mRate;
+
+    private boolean mAnimating;
+    private float mAnimatedValue; // higher precision copy of mCurrentValue
+    private long mLastFrameTimeNanos;
+
+    private boolean mFirstTime = true;
+
+    public RampAnimator(T object, IntProperty<T> property) {
+        mObject = object;
+        mProperty = property;
+        mChoreographer = Choreographer.getInstance();
+    }
+
+    /**
+     * Starts animating towards the specified value.
+     *
+     * If this is the first time the property is being set, the value jumps
+     * directly to the target.
+     *
+     * @param target The target value.
+     * @param rate The convergence rate, in units per second.
+     * @return True if the target differs from the previous target.
+     */
+    public boolean animateTo(int target, int rate) {
+        // Immediately jump to the target the first time.
+        if (mFirstTime) {
+            mFirstTime = false;
+            mProperty.setValue(mObject, target);
+            mCurrentValue = target;
+            return true;
+        }
+
+        // Adjust the rate based on the closest target.
+        // If a faster rate is specified, then use the new rate so that we converge
+        // more rapidly based on the new request.
+        // If a slower rate is specified, then use the new rate only if the current
+        // value is somewhere in between the new and the old target meaning that
+        // we will be ramping in a different direction to get there.
+        // Otherwise, continue at the previous rate.
+        if (!mAnimating
+                || rate > mRate
+                || (target <= mCurrentValue && mCurrentValue <= mTargetValue)
+                || (mTargetValue <= mCurrentValue && mCurrentValue <= target)) {
+            mRate = rate;
+        }
+
+        final boolean changed = (mTargetValue != target);
+        mTargetValue = target;
+
+        // Start animating.
+        if (!mAnimating && target != mCurrentValue) {
+            mAnimating = true;
+            mAnimatedValue = mCurrentValue;
+            mLastFrameTimeNanos = System.nanoTime();
+            postCallback();
+        }
+
+        return changed;
+    }
+
+    private void postCallback() {
+        mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, mCallback, null);
+    }
+
+    private final Runnable mCallback = new Runnable() {
+        @Override // Choreographer callback
+        public void run() {
+            final long frameTimeNanos = mChoreographer.getFrameTimeNanos();
+            final float timeDelta = (frameTimeNanos - mLastFrameTimeNanos)
+                    * 0.000000001f;
+            final float amount = timeDelta * mRate / ValueAnimator.getDurationScale();
+            mLastFrameTimeNanos = frameTimeNanos;
+
+            // Advance the animated value towards the target at the specified rate
+            // and clamp to the target. This gives us the new current value but
+            // we keep the animated value around to allow for fractional increments
+            // towards the target.
+            int oldCurrentValue = mCurrentValue;
+            if (mTargetValue > mCurrentValue) {
+                mAnimatedValue = Math.min(mAnimatedValue + amount, mTargetValue);
+            } else {
+                mAnimatedValue = Math.max(mAnimatedValue - amount, mTargetValue);
+            }
+            mCurrentValue = (int)Math.round(mAnimatedValue);
+
+            if (oldCurrentValue != mCurrentValue) {
+                mProperty.setValue(mObject, mCurrentValue);
+            }
+
+            if (mTargetValue != mCurrentValue) {
+                postCallback();
+            } else {
+                mAnimating = false;
+            }
+        }
+    };
+}