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 */
16package android.transition;
17
18import android.graphics.Rect;
19import android.view.View;
20import 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 */
32public 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