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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 = 0xFFE8EAED;
     35     private static final int DEFAULT_TRACK_COLOR = 0x4CFFFFFF;
     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     private final int mMaskThickness;
     42 
     43     public RoundScrollbarRenderer(View parent) {
     44         // Paints for the round scrollbar.
     45         // Set up the thumb paint
     46         mThumbPaint.setAntiAlias(true);
     47         mThumbPaint.setStrokeCap(Paint.Cap.ROUND);
     48         mThumbPaint.setStyle(Paint.Style.STROKE);
     49 
     50         // Set up the track paint
     51         mTrackPaint.setAntiAlias(true);
     52         mTrackPaint.setStrokeCap(Paint.Cap.ROUND);
     53         mTrackPaint.setStyle(Paint.Style.STROKE);
     54 
     55         mParent = parent;
     56 
     57         // Fetch the resource indicating the thickness of CircularDisplayMask, rounding in the same
     58         // way WindowManagerService.showCircularMask does. The scroll bar is inset by this amount so
     59         // that it doesn't get clipped.
     60         mMaskThickness = parent.getContext().getResources().getDimensionPixelSize(
     61                 com.android.internal.R.dimen.circular_display_mask_thickness);
     62     }
     63 
     64     public void drawRoundScrollbars(Canvas canvas, float alpha, Rect bounds) {
     65         if (alpha == 0) {
     66             return;
     67         }
     68         // Get information about the current scroll state of the parent view.
     69         float maxScroll = mParent.computeVerticalScrollRange();
     70         float scrollExtent = mParent.computeVerticalScrollExtent();
     71         if (scrollExtent <= 0 || maxScroll <= scrollExtent) {
     72             return;
     73         }
     74         float currentScroll = Math.max(0, mParent.computeVerticalScrollOffset());
     75         float linearThumbLength = mParent.computeVerticalScrollExtent();
     76         float thumbWidth = mParent.getWidth() * WIDTH_PERCENTAGE;
     77         mThumbPaint.setStrokeWidth(thumbWidth);
     78         mTrackPaint.setStrokeWidth(thumbWidth);
     79 
     80         setThumbColor(applyAlpha(DEFAULT_THUMB_COLOR, alpha));
     81         setTrackColor(applyAlpha(DEFAULT_TRACK_COLOR, alpha));
     82 
     83         // Normalize the sweep angle for the scroll bar.
     84         float sweepAngle = (linearThumbLength / maxScroll) * SCROLLBAR_ANGLE_RANGE;
     85         sweepAngle = clamp(sweepAngle, MIN_SCROLLBAR_ANGLE_SWIPE, MAX_SCROLLBAR_ANGLE_SWIPE);
     86         // Normalize the start angle so that it falls on the track.
     87         float startAngle = (currentScroll * (SCROLLBAR_ANGLE_RANGE - sweepAngle))
     88                 / (maxScroll - linearThumbLength) - SCROLLBAR_ANGLE_RANGE / 2;
     89         startAngle = clamp(startAngle, -SCROLLBAR_ANGLE_RANGE / 2,
     90                 SCROLLBAR_ANGLE_RANGE / 2 - sweepAngle);
     91 
     92         // Draw the track and the thumb.
     93         float inset = thumbWidth / 2 + mMaskThickness;
     94         mRect.set(
     95                 bounds.left + inset,
     96                 bounds.top + inset,
     97                 bounds.right - inset,
     98                 bounds.bottom - inset);
     99         canvas.drawArc(mRect, -SCROLLBAR_ANGLE_RANGE / 2, SCROLLBAR_ANGLE_RANGE, false,
    100                 mTrackPaint);
    101         canvas.drawArc(mRect, startAngle, sweepAngle, false, mThumbPaint);
    102     }
    103 
    104     private static float clamp(float val, float min, float max) {
    105         if (val < min) {
    106             return min;
    107         } else if (val > max) {
    108             return max;
    109         } else {
    110             return val;
    111         }
    112     }
    113 
    114     private static int applyAlpha(int color, float alpha) {
    115         int alphaByte = (int) (Color.alpha(color) * alpha);
    116         return Color.argb(alphaByte, Color.red(color), Color.green(color), Color.blue(color));
    117     }
    118 
    119     private void setThumbColor(int thumbColor) {
    120         if (mThumbPaint.getColor() != thumbColor) {
    121             mThumbPaint.setColor(thumbColor);
    122         }
    123     }
    124 
    125     private void setTrackColor(int trackColor) {
    126         if (mTrackPaint.getColor() != trackColor) {
    127             mTrackPaint.setColor(trackColor);
    128         }
    129     }
    130 }
    131