content: /*
   * 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.graphics.Rect;
  import android.view.View;
  import android.view.ViewGroup;
  
  /**
   * A propagation that varies with the distance to the epicenter of the Transition
   * or center of the scene if no epicenter exists. When a View is visible in the
   * start of the transition, Views farther from the epicenter will transition
   * sooner than Views closer to the epicenter. When a View is not in the start
   * of the transition or is not visible at the start of the transition, it will
   * transition sooner when closer to the epicenter and later when farther from
   * the epicenter. This is the default TransitionPropagation used with
   * {@link android.transition.Explode}.
   */
  public class CircularPropagation extends VisibilityPropagation {
      private static final String TAG = "CircularPropagation";
  
      private float mPropagationSpeed = 3.0f;
  
      /**
       * Sets the speed at which transition propagation happens, relative to the duration of the
       * Transition. A <code>propagationSpeed</code> of 1 means that a View centered farthest from
       * the epicenter and View centered at the epicenter will have a difference
       * in start delay of approximately the duration of the Transition. A speed of 2 means the
       * start delay difference will be approximately half of the duration of the transition. A
       * value of 0 is illegal, but negative values will invert the propagation.
       *
       * @param propagationSpeed The speed at which propagation occurs, relative to the duration
       *                         of the transition. A speed of 4 means it works 4 times as fast
       *                         as the duration of the transition. May not be 0.
       */
      public void setPropagationSpeed(float propagationSpeed) {
          if (propagationSpeed == 0) {
              throw new IllegalArgumentException("propagationSpeed may not be 0");
          }
          mPropagationSpeed = propagationSpeed;
      }
  
      @Override
      public long getStartDelay(ViewGroup sceneRoot, Transition transition,
              TransitionValues startValues, TransitionValues endValues) {
          if (startValues == null && endValues == null) {
              return 0;
          }
          int directionMultiplier = 1;
          TransitionValues positionValues;
          if (endValues == null || getViewVisibility(startValues) == View.VISIBLE) {
              positionValues = startValues;
              directionMultiplier = -1;
          } else {
              positionValues = endValues;
          }
  
          int viewCenterX = getViewX(positionValues);
          int viewCenterY = getViewY(positionValues);
  
          Rect epicenter = transition.getEpicenter();
          int epicenterX;
          int epicenterY;
          if (epicenter != null) {
              epicenterX = epicenter.centerX();
              epicenterY = epicenter.centerY();
          } else {
              int[] loc = new int[2];
              sceneRoot.getLocationOnScreen(loc);
              epicenterX = Math.round(loc[0] + (sceneRoot.getWidth() / 2)
                      + sceneRoot.getTranslationX());
              epicenterY = Math.round(loc[1] + (sceneRoot.getHeight() / 2)
                      + sceneRoot.getTranslationY());
          }
          double distance = distance(viewCenterX, viewCenterY, epicenterX, epicenterY);
          double maxDistance = distance(0, 0, sceneRoot.getWidth(), sceneRoot.getHeight());
          double distanceFraction = distance/maxDistance;
  
          long duration = transition.getDuration();
          if (duration < 0) {
              duration = 300;
          }
  
          return Math.round(duration * directionMultiplier / mPropagationSpeed * distanceFraction);
      }
  
      private static double distance(float x1, float y1, float x2, float y2) {
          double x = x2 - x1;
          double y = y2 - y1;
          return Math.hypot(x, y);
      }
  }
  