for (int i = 0; i < mPointCount; i++) {
 canvas.getClipBounds(mCanvasClipBounds);
 canvas.drawPoint(mCanvasClipBounds.centerX() + (i - mPointCount / 2) * mPointMargin,
     mCanvasClipBounds.centerY(), mPointPaint);
}

private void drawDegreeText(int degrees, Canvas canvas, boolean canReach) {
 canvas.drawText(degrees + "°",
    getWidth() / 2 + mPointMargin * degrees / 2 - mTextWidths[0] / 2 * 3 - mCurrentDegrees / 2 * mPointMargin,
     getHeight() / 2 - 10,
     mTextPaint);
 }
}

drawDegreeText(0, canvas, true);
drawDegreeText(15, canvas, true);
drawDegreeText(30, canvas, true);
drawDegreeText(45, canvas, true);
drawDegreeText(-15, canvas, true);
drawDegreeText(-30, canvas, true);
drawDegreeText(-45, canvas, true);

drawDegreeText(60, canvas, false);
drawDegreeText(75, canvas, false);
drawDegreeText(90, canvas, false);
drawDegreeText(-60, canvas, false);
drawDegreeText(-75, canvas, false);
drawDegreeText(-90, canvas, false);

//画当前角度
if (mCurrentDegrees >= 10) {
 canvas.drawText(mCurrentDegrees + "°", getWidth() / 2 - mTextWidths[0], mBaseLine, mTextPaint);
} else if (mCurrentDegrees <= -10) {
 canvas.drawText(mCurrentDegrees + "°", getWidth() / 2 - mTextWidths[0] / 2 * 3, mBaseLine, mTextPaint);
} else if (mCurrentDegrees < 0) {
 canvas.drawText(mCurrentDegrees + "°", getWidth() / 2 - mTextWidths[0], mBaseLine, mTextPaint);
} else {
 canvas.drawText(mCurrentDegrees + "°", getWidth() / 2 - mTextWidths[0] / 2, mBaseLine, mTextPaint);
}

//三角指示器的Path
mIndicatorPath.moveTo(w / 2, h / 2 + mFontMetrics.top / 2 - 18);
mIndicatorPath.rLineTo(-8, -8);
mIndicatorPath.rLineTo(16, 0);

 for (int i = 0; i < mPointCount; i++) {

  if (i > zeroIndex - 22 && i < zeroIndex + 22 && mScrollStarted) {
   mPointPaint.setAlpha(255);
  } else {
   mPointPaint.setAlpha(100);
  }

  if (i > mPointCount / 2 - 8 && i < mPointCount / 2 + 8
    && i > zeroIndex - 22 && i < zeroIndex + 22) {
   if (mScrollStarted)
    mPointPaint.setAlpha(Math.abs(mPointCount / 2 - i) * 255 / 8);
   else
    mPointPaint.setAlpha(Math.abs(mPointCount / 2 - i) * 100 / 8);
  }
  ……
 }

@Override
public boolean onTouchEvent(MotionEvent event) {
 switch (event.getAction()) {
  ……
  case MotionEvent.ACTION_MOVE:
   float distance = event.getX() - mLastTouchedPosition;
   ……
   if (distance != 0) {
    onScrollEvent(event, distance);
   }
   break;
  }
  ……
  return true;
}

private void onScrollEvent(MotionEvent event, float distance) {
 mTotalScrollDistance -= distance;
 postInvalidate();
 mLastTouchedPosition = event.getX();
 mCurrentDegrees = (int) ((mTotalScrollDistance * mDragFactor) / mPointMargin);
 if (mScrollingListener != null) {
  mScrollingListener.onScroll(mCurrentDegrees);
 }
}