-/* Return the cost of drawing line VPOS in MATRIX. The cost equals
- the number of characters in the line. If must_write_spaces is
- zero, leading and trailing spaces are ignored. */
+/* Return the cost of drawing line VPOS in MATRIX, which may
+ be current or desired matrix of frame F. The cost equals
+ the number of characters in the line. If must_write_spaces
+ is zero, leading and trailing spaces are ignored. */