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      */
setPropagationSpeed(float propagationSpeed)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
getStartDelay(ViewGroup sceneRoot, Transition transition, TransitionValues startValues, TransitionValues endValues)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 
distance(float x1, float y1, float x2, float y2)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