content: /*
   * 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;
  
  import android.annotation.UnsupportedAppUsage;
  
  /**
   * This evaluator can be used to perform type interpolation between integer
   * values that represent ARGB colors.
   */
  public class ArgbEvaluator implements TypeEvaluator {
      private static final ArgbEvaluator sInstance = new ArgbEvaluator();
  
      /**
       * Returns an instance of <code>ArgbEvaluator</code> that may be used in
       * {@link ValueAnimator#setEvaluator(TypeEvaluator)}. The same instance may
       * be used in multiple <code>Animator</code>s because it holds no state.
       * @return An instance of <code>ArgbEvalutor</code>.
       *
       * @hide
       */
      @UnsupportedAppUsage
      public static ArgbEvaluator getInstance() {
          return sInstance;
      }
  
      /**
       * This function returns the calculated in-between value for a color
       * given integers that represent the start and end values in the four
       * bytes of the 32-bit int. Each channel is separately linearly interpolated
       * and the resulting calculated values are recombined into the return value.
       *
       * @param fraction The fraction from the starting to the ending values
       * @param startValue A 32-bit int value representing colors in the
       * separate bytes of the parameter
       * @param endValue A 32-bit int value representing colors in the
       * separate bytes of the parameter
       * @return A value that is calculated to be the linearly interpolated
       * result, derived by separating the start and end values into separate
       * color channels and interpolating each one separately, recombining the
       * resulting values in the same way.
       */
      public Object evaluate(float fraction, Object startValue, Object endValue) {
          int startInt = (Integer) startValue;
          float startA = ((startInt >> 24) & 0xff) / 255.0f;
          float startR = ((startInt >> 16) & 0xff) / 255.0f;
          float startG = ((startInt >>  8) & 0xff) / 255.0f;
          float startB = ( startInt        & 0xff) / 255.0f;
  
          int endInt = (Integer) endValue;
          float endA = ((endInt >> 24) & 0xff) / 255.0f;
          float endR = ((endInt >> 16) & 0xff) / 255.0f;
          float endG = ((endInt >>  8) & 0xff) / 255.0f;
          float endB = ( endInt        & 0xff) / 255.0f;
  
          // convert from sRGB to linear
          startR = (float) Math.pow(startR, 2.2);
          startG = (float) Math.pow(startG, 2.2);
          startB = (float) Math.pow(startB, 2.2);
  
          endR = (float) Math.pow(endR, 2.2);
          endG = (float) Math.pow(endG, 2.2);
          endB = (float) Math.pow(endB, 2.2);
  
          // compute the interpolated color in linear space
          float a = startA + fraction * (endA - startA);
          float r = startR + fraction * (endR - startR);
          float g = startG + fraction * (endG - startG);
          float b = startB + fraction * (endB - startB);
  
          // convert back to sRGB in the [0..255] range
          a = a * 255.0f;
          r = (float) Math.pow(r, 1.0 / 2.2) * 255.0f;
          g = (float) Math.pow(g, 1.0 / 2.2) * 255.0f;
          b = (float) Math.pow(b, 1.0 / 2.2) * 255.0f;
  
          return Math.round(a) << 24 | Math.round(r) << 16 | Math.round(g) << 8 | Math.round(b);
      }
  }