code: @Override
  	public void draw(Canvas canvas) {
  		float width = canvas.getWidth();
  		float margin = (width / 3) + mState.mMarginSide;
  		float posY = canvas.getHeight() - mState.mMarginBottom;
  		canvas.drawLine(margin, posY, width - margin, posY, mPaint);
  	}
docs: It is based on the canvas width and height instead of the bounds
  in order not to consider the margins of the button it is drawn in.