@Override
        public void draw(Canvas canvas, Paint paint) {
            final int viewWidth = getBounds().width();
            final int viewHeight = getBounds().height();
            canvas.drawCircle(viewWidth / 2, viewHeight / 2, (mCircleDiameter / 2 + mShadowRadius),
                    mShadowPaint);
            canvas.drawCircle(viewWidth / 2, viewHeight / 2, (mCircleDiameter / 2), paint);
        }
Taken from {@link package android.support.v4.widget}
common/src/main/java/com/sxjs/common/widget/pulltorefresh/header/MaterialProgressDrawable.java