api-impl: borrow several classes form AOSP master (cca 42a0e321e226fe0f678ff15d9293b03bcd606b96)

src/api-impl/android/animation/FloatEvaluator.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2010 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.animation;
+
+/**
+ * This evaluator can be used to perform type interpolation between <code>float</code> values.
+ */
+public class FloatEvaluator /*implements TypeEvaluator<Number>*/ {
+
+	/**
+	 * This function returns the result of linearly interpolating the start and end values, with
+	 * <code>fraction</code> representing the proportion between the start and end values. The
+	 * calculation is a simple parametric calculation: <code>result = x0 + t * (x1 - x0)</code>,
+	 * where <code>x0</code> is <code>startValue</code>, <code>x1</code> is <code>endValue</code>,
+	 * and <code>t</code> is <code>fraction</code>.
+	 *
+	 * @param fraction   The fraction from the starting to the ending values
+	 * @param startValue The start value; should be of type <code>float</code> or
+	 *                   <code>Float</code>
+	 * @param endValue   The end value; should be of type <code>float</code> or <code>Float</code>
+	 * @return A linear interpolation between the start and end values, given the
+	 *         <code>fraction</code> parameter.
+	 */
+	public Float evaluate(float fraction, Number startValue, Number endValue) {
+		float startFloat = startValue.floatValue();
+		return startFloat + fraction * (endValue.floatValue() - startFloat);
+	}
+}