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      1 /*
      2  * Copyright (C) 2014 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 package android.transition;
     17 
     18 import android.graphics.Rect;
     19 import android.view.View;
     20 import android.view.ViewGroup;
     21 
     22 /**
     23  * A propagation that varies with the distance to the epicenter of the Transition
     24  * or center of the scene if no epicenter exists. When a View is visible in the
     25  * start of the transition, Views farther from the epicenter will transition
     26  * sooner than Views closer to the epicenter. When a View is not in the start
     27  * of the transition or is not visible at the start of the transition, it will
     28  * transition sooner when closer to the epicenter and later when farther from
     29  * the epicenter. This is the default TransitionPropagation used with
     30  * {@link android.transition.Explode}.
     31  */
     32 public class CircularPropagation extends VisibilityPropagation {
     33     private static final String TAG = "CircularPropagation";
     34 
     35     private float mPropagationSpeed = 3.0f;
     36 
     37     /**
     38      * Sets the speed at which transition propagation happens, relative to the duration of the
     39      * Transition. A <code>propagationSpeed</code> of 1 means that a View centered farthest from
     40      * the epicenter and View centered at the epicenter will have a difference
     41      * in start delay of approximately the duration of the Transition. A speed of 2 means the
     42      * start delay difference will be approximately half of the duration of the transition. A
     43      * value of 0 is illegal, but negative values will invert the propagation.
     44      *
     45      * @param propagationSpeed The speed at which propagation occurs, relative to the duration
     46      *                         of the transition. A speed of 4 means it works 4 times as fast
     47      *                         as the duration of the transition. May not be 0.
     48      */
     49     public void setPropagationSpeed(float propagationSpeed) {
     50         if (propagationSpeed == 0) {
     51             throw new IllegalArgumentException("propagationSpeed may not be 0");
     52         }
     53         mPropagationSpeed = propagationSpeed;
     54     }
     55 
     56     @Override
     57     public long getStartDelay(ViewGroup sceneRoot, Transition transition,
     58             TransitionValues startValues, TransitionValues endValues) {
     59         if (startValues == null && endValues == null) {
     60             return 0;
     61         }
     62         int directionMultiplier = 1;
     63         TransitionValues positionValues;
     64         if (endValues == null || getViewVisibility(startValues) == View.VISIBLE) {
     65             positionValues = startValues;
     66             directionMultiplier = -1;
     67         } else {
     68             positionValues = endValues;
     69         }
     70 
     71         int viewCenterX = getViewX(positionValues);
     72         int viewCenterY = getViewY(positionValues);
     73 
     74         Rect epicenter = transition.getEpicenter();
     75         int epicenterX;
     76         int epicenterY;
     77         if (epicenter != null) {
     78             epicenterX = epicenter.centerX();
     79             epicenterY = epicenter.centerY();
     80         } else {
     81             int[] loc = new int[2];
     82             sceneRoot.getLocationOnScreen(loc);
     83             epicenterX = Math.round(loc[0] + (sceneRoot.getWidth() / 2)
     84                     + sceneRoot.getTranslationX());
     85             epicenterY = Math.round(loc[1] + (sceneRoot.getHeight() / 2)
     86                     + sceneRoot.getTranslationY());
     87         }
     88         double distance = distance(viewCenterX, viewCenterY, epicenterX, epicenterY);
     89         double maxDistance = distance(0, 0, sceneRoot.getWidth(), sceneRoot.getHeight());
     90         double distanceFraction = distance/maxDistance;
     91 
     92         long duration = transition.getDuration();
     93         if (duration < 0) {
     94             duration = 300;
     95         }
     96 
     97         return Math.round(duration * directionMultiplier / mPropagationSpeed * distanceFraction);
     98     }
     99 
    100     private static double distance(float x1, float y1, float x2, float y2) {
    101         double x = x2 - x1;
    102         double y = y2 - y1;
    103         return Math.hypot(x, y);
    104     }
    105 }
    106