code: func fillDrawOp(styleStr string) (opStr string) {
  	switch strings.ToUpper(styleStr) {
  	case "", "D":
  		// Stroke the path.
  		opStr = "S"
  	case "F":
  		// fill the path, using the nonzero winding number rule
  		opStr = "f"
  	case "F*":
  		// fill the path, using the even-odd rule
  		opStr = "f*"
  	case "FD", "DF":
  		// fill and then stroke the path, using the nonzero winding number rule
  		opStr = "B"
  	case "FD*", "DF*":
  		// fill and then stroke the path, using the even-odd rule
  		opStr = "B*"
  	default:
  		opStr = styleStr
  	}
  	return
  }
docs: // fillDrawOp corrects path painting operators