content: /*
   * Copyright (C) 2016 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.view;
  
  import android.graphics.Canvas;
  import android.graphics.Color;
  import android.graphics.Paint;
  import android.graphics.Rect;
  import android.graphics.RectF;
  
  /**
   * Helper class for drawing round scroll bars on round Wear devices.
   */
  class RoundScrollbarRenderer {
      // The range of the scrollbar position represented as an angle in degrees.
      private static final int SCROLLBAR_ANGLE_RANGE = 90;
      private static final int MAX_SCROLLBAR_ANGLE_SWIPE = 16;
      private static final int MIN_SCROLLBAR_ANGLE_SWIPE = 6;
      private static final float WIDTH_PERCENTAGE = 0.02f;
      private static final int DEFAULT_THUMB_COLOR = 0xFFE8EAED;
      private static final int DEFAULT_TRACK_COLOR = 0x4CFFFFFF;
  
      private final Paint mThumbPaint = new Paint();
      private final Paint mTrackPaint = new Paint();
      private final RectF mRect = new RectF();
      private final View mParent;
      private final int mMaskThickness;
  
      public RoundScrollbarRenderer(View parent) {
          // Paints for the round scrollbar.
          // Set up the thumb paint
          mThumbPaint.setAntiAlias(true);
          mThumbPaint.setStrokeCap(Paint.Cap.ROUND);
          mThumbPaint.setStyle(Paint.Style.STROKE);
  
          // Set up the track paint
          mTrackPaint.setAntiAlias(true);
          mTrackPaint.setStrokeCap(Paint.Cap.ROUND);
          mTrackPaint.setStyle(Paint.Style.STROKE);
  
          mParent = parent;
  
          // Fetch the resource indicating the thickness of CircularDisplayMask, rounding in the same
          // way WindowManagerService.showCircularMask does. The scroll bar is inset by this amount so
          // that it doesn't get clipped.
          mMaskThickness = parent.getContext().getResources().getDimensionPixelSize(
                  com.android.internal.R.dimen.circular_display_mask_thickness);
      }
  
      public void drawRoundScrollbars(Canvas canvas, float alpha, Rect bounds) {
          if (alpha == 0) {
              return;
          }
          // Get information about the current scroll state of the parent view.
          float maxScroll = mParent.computeVerticalScrollRange();
          float scrollExtent = mParent.computeVerticalScrollExtent();
          if (scrollExtent <= 0 || maxScroll <= scrollExtent) {
              return;
          }
          float currentScroll = Math.max(0, mParent.computeVerticalScrollOffset());
          float linearThumbLength = mParent.computeVerticalScrollExtent();
          float thumbWidth = mParent.getWidth() * WIDTH_PERCENTAGE;
          mThumbPaint.setStrokeWidth(thumbWidth);
          mTrackPaint.setStrokeWidth(thumbWidth);
  
          setThumbColor(applyAlpha(DEFAULT_THUMB_COLOR, alpha));
          setTrackColor(applyAlpha(DEFAULT_TRACK_COLOR, alpha));
  
          // Normalize the sweep angle for the scroll bar.
          float sweepAngle = (linearThumbLength / maxScroll) * SCROLLBAR_ANGLE_RANGE;
          sweepAngle = clamp(sweepAngle, MIN_SCROLLBAR_ANGLE_SWIPE, MAX_SCROLLBAR_ANGLE_SWIPE);
          // Normalize the start angle so that it falls on the track.
          float startAngle = (currentScroll * (SCROLLBAR_ANGLE_RANGE - sweepAngle))
                  / (maxScroll - linearThumbLength) - SCROLLBAR_ANGLE_RANGE / 2;
          startAngle = clamp(startAngle, -SCROLLBAR_ANGLE_RANGE / 2,
                  SCROLLBAR_ANGLE_RANGE / 2 - sweepAngle);
  
          // Draw the track and the thumb.
          float inset = thumbWidth / 2 + mMaskThickness;
          mRect.set(
                  bounds.left + inset,
                  bounds.top + inset,
                  bounds.right - inset,
                  bounds.bottom - inset);
          canvas.drawArc(mRect, -SCROLLBAR_ANGLE_RANGE / 2, SCROLLBAR_ANGLE_RANGE, false,
                  mTrackPaint);
          canvas.drawArc(mRect, startAngle, sweepAngle, false, mThumbPaint);
      }
  
      private static float clamp(float val, float min, float max) {
          if (val < min) {
              return min;
          } else if (val > max) {
              return max;
          } else {
              return val;
          }
      }
  
      private static int applyAlpha(int color, float alpha) {
          int alphaByte = (int) (Color.alpha(color) * alpha);
          return Color.argb(alphaByte, Color.red(color), Color.green(color), Color.blue(color));
      }
  
      private void setThumbColor(int thumbColor) {
          if (mThumbPaint.getColor() != thumbColor) {
              mThumbPaint.setColor(thumbColor);
          }
      }
  
      private void setTrackColor(int trackColor) {
          if (mTrackPaint.getColor() != trackColor) {
              mTrackPaint.setColor(trackColor);
          }
      }
  }
  