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      1 /*
      2  * Copyright (C) 2010 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.animation;
     18 
     19 /**
     20  * This evaluator can be used to perform type interpolation between integer
     21  * values that represent ARGB colors.
     22  */
     23 public class ArgbEvaluator implements TypeEvaluator {
     24     private static final ArgbEvaluator sInstance = new ArgbEvaluator();
     25 
     26     /**
     27      * Returns an instance of <code>ArgbEvaluator</code> that may be used in
     28      * {@link ValueAnimator#setEvaluator(TypeEvaluator)}. The same instance may
     29      * be used in multiple <code>Animator</code>s because it holds no state.
     30      * @return An instance of <code>ArgbEvalutor</code>.
     31      *
     32      * @hide
     33      */
     34     public static ArgbEvaluator getInstance() {
     35         return sInstance;
     36     }
     37 
     38     /**
     39      * This function returns the calculated in-between value for a color
     40      * given integers that represent the start and end values in the four
     41      * bytes of the 32-bit int. Each channel is separately linearly interpolated
     42      * and the resulting calculated values are recombined into the return value.
     43      *
     44      * @param fraction The fraction from the starting to the ending values
     45      * @param startValue A 32-bit int value representing colors in the
     46      * separate bytes of the parameter
     47      * @param endValue A 32-bit int value representing colors in the
     48      * separate bytes of the parameter
     49      * @return A value that is calculated to be the linearly interpolated
     50      * result, derived by separating the start and end values into separate
     51      * color channels and interpolating each one separately, recombining the
     52      * resulting values in the same way.
     53      */
     54     public Object evaluate(float fraction, Object startValue, Object endValue) {
     55         int startInt = (Integer) startValue;
     56         int startA = (startInt >> 24) & 0xff;
     57         int startR = (startInt >> 16) & 0xff;
     58         int startG = (startInt >> 8) & 0xff;
     59         int startB = startInt & 0xff;
     60 
     61         int endInt = (Integer) endValue;
     62         int endA = (endInt >> 24) & 0xff;
     63         int endR = (endInt >> 16) & 0xff;
     64         int endG = (endInt >> 8) & 0xff;
     65         int endB = endInt & 0xff;
     66 
     67         return (int)((startA + (int)(fraction * (endA - startA))) << 24) |
     68                 (int)((startR + (int)(fraction * (endR - startR))) << 16) |
     69                 (int)((startG + (int)(fraction * (endG - startG))) << 8) |
     70                 (int)((startB + (int)(fraction * (endB - startB))));
     71     }
     72 }