1 /*
2  * Copyright (C) 2016 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 
17 package android.view;
18 
19 import android.graphics.Canvas;
20 import android.graphics.Color;
21 import android.graphics.Paint;
22 import android.graphics.Rect;
23 import android.graphics.RectF;
24 
25 /**
26  * Helper class for drawing round scroll bars on round Wear devices.
27  */
28 class RoundScrollbarRenderer {
29     // The range of the scrollbar position represented as an angle in degrees.
30     private static final int SCROLLBAR_ANGLE_RANGE = 90;
31     private static final int MAX_SCROLLBAR_ANGLE_SWIPE = 16;
32     private static final int MIN_SCROLLBAR_ANGLE_SWIPE = 6;
33     private static final float WIDTH_PERCENTAGE = 0.02f;
34     private static final int DEFAULT_THUMB_COLOR = 0x4CFFFFFF;
35     private static final int DEFAULT_TRACK_COLOR = 0x26FFFFFF;
36 
37     private final Paint mThumbPaint = new Paint();
38     private final Paint mTrackPaint = new Paint();
39     private final RectF mRect = new RectF();
40     private final View mParent;
41 
RoundScrollbarRenderer(View parent)42     public RoundScrollbarRenderer(View parent) {
43         // Paints for the round scrollbar.
44         // Set up the thumb paint
45         mThumbPaint.setAntiAlias(true);
46         mThumbPaint.setStrokeCap(Paint.Cap.ROUND);
47         mThumbPaint.setStyle(Paint.Style.STROKE);
48 
49         // Set up the track paint
50         mTrackPaint.setAntiAlias(true);
51         mTrackPaint.setStrokeCap(Paint.Cap.ROUND);
52         mTrackPaint.setStyle(Paint.Style.STROKE);
53 
54         mParent = parent;
55     }
56 
drawRoundScrollbars(Canvas canvas, float alpha, Rect bounds)57     public void drawRoundScrollbars(Canvas canvas, float alpha, Rect bounds) {
58         if (alpha == 0) {
59             return;
60         }
61         // Get information about the current scroll state of the parent view.
62         float maxScroll = mParent.computeVerticalScrollRange();
63         float scrollExtent = mParent.computeVerticalScrollExtent();
64         if (scrollExtent <= 0 || maxScroll <= scrollExtent) {
65             return;
66         }
67         float currentScroll = Math.max(0, mParent.computeVerticalScrollOffset());
68         float linearThumbLength = mParent.computeVerticalScrollExtent();
69         float thumbWidth = mParent.getWidth() * WIDTH_PERCENTAGE;
70         mThumbPaint.setStrokeWidth(thumbWidth);
71         mTrackPaint.setStrokeWidth(thumbWidth);
72 
73         setThumbColor(applyAlpha(DEFAULT_THUMB_COLOR, alpha));
74         setTrackColor(applyAlpha(DEFAULT_TRACK_COLOR, alpha));
75 
76         // Normalize the sweep angle for the scroll bar.
77         float sweepAngle = (linearThumbLength / maxScroll) * SCROLLBAR_ANGLE_RANGE;
78         sweepAngle = clamp(sweepAngle, MIN_SCROLLBAR_ANGLE_SWIPE, MAX_SCROLLBAR_ANGLE_SWIPE);
79         // Normalize the start angle so that it falls on the track.
80         float startAngle = (currentScroll * (SCROLLBAR_ANGLE_RANGE - sweepAngle))
81                 / (maxScroll - linearThumbLength) - SCROLLBAR_ANGLE_RANGE / 2;
82         startAngle = clamp(startAngle, -SCROLLBAR_ANGLE_RANGE / 2,
83                 SCROLLBAR_ANGLE_RANGE / 2 - sweepAngle);
84 
85         // Draw the track and the scroll bar.
86         mRect.set(
87                 bounds.left - thumbWidth / 2,
88                 bounds.top,
89                 bounds.right - thumbWidth / 2,
90                 bounds.bottom);
91 
92         canvas.drawArc(mRect, -SCROLLBAR_ANGLE_RANGE / 2, SCROLLBAR_ANGLE_RANGE, false,
93                 mTrackPaint);
94         canvas.drawArc(mRect, startAngle, sweepAngle, false, mThumbPaint);
95     }
96 
clamp(float val, float min, float max)97     private static float clamp(float val, float min, float max) {
98         if (val < min) {
99             return min;
100         } else if (val > max) {
101             return max;
102         } else {
103             return val;
104         }
105     }
106 
applyAlpha(int color, float alpha)107     private static int applyAlpha(int color, float alpha) {
108         int alphaByte = (int) (Color.alpha(color) * alpha);
109         return Color.argb(alphaByte, Color.red(color), Color.green(color), Color.blue(color));
110     }
111 
setThumbColor(int thumbColor)112     private void setThumbColor(int thumbColor) {
113         if (mThumbPaint.getColor() != thumbColor) {
114             mThumbPaint.setColor(thumbColor);
115         }
116     }
117 
setTrackColor(int trackColor)118     private void setTrackColor(int trackColor) {
119         if (mTrackPaint.getColor() != trackColor) {
120             mTrackPaint.setColor(trackColor);
121         }
122     }
123 }
124