CurvingLayoutCallback.java revision 9b028c55b13889bf75b5dd43b5b0f4051834ae1d 
1/*
2 * Copyright (C) 2017 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
17package android.support.wear.widget;
18
19import android.content.Context;
20import android.graphics.Path;
21import android.graphics.PathMeasure;
22import android.support.annotation.VisibleForTesting;
23import android.support.v7.widget.RecyclerView;
24import android.support.wear.R;
25import android.view.View;
26
27/**
28 * An implementation of the {@link WearableLinearLayoutManager.LayoutCallback} aligning the children
29 * of the associated {@link WearableRecyclerView} along a pre-defined vertical curve.
30 */
31public class CurvingLayoutCallback extends WearableLinearLayoutManager.LayoutCallback {
32    private static final float EPSILON = 0.001f;
33
34    private final Path mCurvePath;
35    private final PathMeasure mPathMeasure;
36    private int mCurvePathHeight;
37    private int mXCurveOffset;
38    private float mPathLength;
39    private float mCurveBottom;
40    private float mCurveTop;
41    private float mLineGradient;
42    private final float[] mPathPoints = new float[2];
43    private final float[] mPathTangent = new float[2];
44    private final float[] mAnchorOffsetXY = new float[2];
45
46    private RecyclerView mParentView;
47    private boolean mIsScreenRound;
48    private int mLayoutWidth;
49    private int mLayoutHeight;
50
51    public CurvingLayoutCallback(Context context) {
52        mCurvePath = new Path();
53        mPathMeasure = new PathMeasure();
54        mIsScreenRound = context.getResources().getConfiguration().isScreenRound();
55        mXCurveOffset = context.getResources().getDimensionPixelSize(
56                R.dimen.wrv_curve_default_x_offset);
57    }
58
59    @Override
60    public void onLayoutFinished(View child, RecyclerView parent) {
61        if (mParentView != parent || (mParentView != null && (
62                mParentView.getWidth() != parent.getWidth()
63                        || mParentView.getHeight() != parent.getHeight()))) {
64            mParentView = parent;
65            mLayoutWidth = mParentView.getWidth();
66            mLayoutHeight = mParentView.getHeight();
67        }
68        if (mIsScreenRound) {
69            maybeSetUpCircularInitialLayout(mLayoutWidth, mLayoutHeight);
70            mAnchorOffsetXY[0] = mXCurveOffset;
71            mAnchorOffsetXY[1] = child.getHeight() / 2.0f;
72            adjustAnchorOffsetXY(child, mAnchorOffsetXY);
73            float minCenter = -(float) child.getHeight() / 2;
74            float maxCenter = mLayoutHeight + (float) child.getHeight() / 2;
75            float range = maxCenter - minCenter;
76            float verticalAnchor = (float) child.getTop() + mAnchorOffsetXY[1];
77            float mYScrollProgress = (verticalAnchor + Math.abs(minCenter)) / range;
78
79            mPathMeasure.getPosTan(mYScrollProgress * mPathLength, mPathPoints, mPathTangent);
80
81            boolean topClusterRisk =
82                    Math.abs(mPathPoints[1] - mCurveBottom) < EPSILON
83                            && minCenter < mPathPoints[1];
84            boolean bottomClusterRisk =
85                    Math.abs(mPathPoints[1] - mCurveTop) < EPSILON
86                            && maxCenter > mPathPoints[1];
87            // Continue offsetting the child along the straight-line part of the curve, if it
88            // has not gone off the screen when it reached the end of the original curve.
89            if (topClusterRisk || bottomClusterRisk) {
90                mPathPoints[1] = verticalAnchor;
91                mPathPoints[0] = (Math.abs(verticalAnchor) * mLineGradient);
92            }
93
94            // Offset the View to match the provided anchor point.
95            int newLeft = (int) (mPathPoints[0] - mAnchorOffsetXY[0]);
96            child.offsetLeftAndRight(newLeft - child.getLeft());
97            float verticalTranslation = mPathPoints[1] - verticalAnchor;
98            child.setTranslationY(verticalTranslation);
99        } else {
100            child.setTranslationY(0);
101        }
102    }
103
104    /**
105     * Override this method if you wish to adjust the anchor coordinates for each child view
106     * during a layout pass. In the override set the new desired anchor coordinates in
107     * the provided array. The coordinates should be provided in relation to the child view.
108     *
109     * @param child          The child view to which the anchor coordinates will apply.
110     * @param anchorOffsetXY The anchor coordinates for the provided child view, by default set
111     *                       to a pre-defined constant on the horizontal axis and half of the
112     *                       child height on the vertical axis (vertical center).
113     */
114    public void adjustAnchorOffsetXY(View child, float[] anchorOffsetXY) {
115        return;
116    };
117
118    @VisibleForTesting
119    void setRound(boolean isScreenRound) {
120        mIsScreenRound = isScreenRound;
121    }
122
123    @VisibleForTesting
124    void setOffset(int offset) {
125        mXCurveOffset = offset;
126    }
127
128    /** Set up the initial layout for round screens. */
129    private void maybeSetUpCircularInitialLayout(int width, int height) {
130        // The values in this function are custom to the curve we use.
131        if (mCurvePathHeight != height) {
132            mCurvePathHeight = height;
133            mCurveBottom = -0.048f * height;
134            mCurveTop = 1.048f * height;
135            mLineGradient = 0.5f / 0.048f;
136            mCurvePath.reset();
137            mCurvePath.moveTo(0.5f * width, mCurveBottom);
138            mCurvePath.lineTo(0.34f * width, 0.075f * height);
139            mCurvePath.cubicTo(
140                    0.22f * width, 0.17f * height, 0.13f * width, 0.32f * height, 0.13f * width,
141                    height / 2);
142            mCurvePath.cubicTo(
143                    0.13f * width,
144                    0.68f * height,
145                    0.22f * width,
146                    0.83f * height,
147                    0.34f * width,
148                    0.925f * height);
149            mCurvePath.lineTo(width / 2, mCurveTop);
150            mPathMeasure.setPath(mCurvePath, false);
151            mPathLength = mPathMeasure.getLength();
152        }
153    }
154}
155