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      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 
     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 
     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 
     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 
    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 
    112     private void setThumbColor(int thumbColor) {
    113         if (mThumbPaint.getColor() != thumbColor) {
    114             mThumbPaint.setColor(thumbColor);
    115         }
    116     }
    117 
    118     private void setTrackColor(int trackColor) {
    119         if (mTrackPaint.getColor() != trackColor) {
    120             mTrackPaint.setColor(trackColor);
    121         }
    122     }
    123 }
    124