| blob | fec922c6160d189bd2ba25b72319b73499958dc3 |
3 ;;; The beaming function takes a list of the form:
4 ;;; ((p1 x1) (p2 x2) ... (pn xn))
5 ;;; where p1 through pn are staff positions (bottom line is 0,
6 ;;; increas upwards by 1 for each staff step) and x1 through xn
7 ;;; are x positions for the clusters given in the same unit as the
8 ;;; positions, i.e., staff steps
10 ;;; The result of the computation is a VALID BEAMING. Such a beaming
11 ;;; is represented as a list of two elements representing the left and
12 ;;; the right end of the primary beam, respectively. Each element is
13 ;;; a cons of two integers, the fist representing the staff line where
14 ;;; the lower line is numbered 0, and so on in steps of two so that
15 ;;; the upper one is numbered 8. The second of the two integers
16 ;;; represents the position of the beam with respect to the staff
17 ;;; line, where 0 means straddle, 1 means sit and -1 means hang. This
18 ;;; representation makes it easy to transform the constellation by
19 ;;; reflection.
21 ;;; Take two vertical positions and compute the beam slant and beam
22 ;;; position for the beam connecting them. A position of zero means
23 ;;; the bottom of the staff. Positive integers count up 1/2 space so
24 ;;; that C on a staff with a G-clef gets to have number -2. Negative
25 ;;; numbers go the other way. This function assumes that pos2 >= pos1,
26 ;;; and that the two notes are sufficiently far apart that the slant
27 ;;; is going to be acceptably small.
107 ;;; take two points of the form (pos x b), where pos is a vertical
108 ;;; position (in staff-steps), x is a horizontal position (also in
109 ;;; staff-steps), and b is the number of beams at that position and
110 ;;; compute a valid beaming for the two points. To do so, first call
111 ;;; the function passed as an argument on the two vertical positions.
112 ;;; If the slant thus obtained is too high, repeat with a slightly
113 ;;; higher vertical position of the first point.
125 beaming)))
127 ;;; main entry
129 ;;; Take a list of the form ((p1 x1 b1) (p2 x2 b2) ... (pn xn bn)),
130 ;;; (where pi is a vertical position, xi is a horizontal position
131 ;;; (both measured in staff-steps), and bi is the number of stems at
132 ;;; that position), a stem direction, and a function to compute a
133 ;;; valid slant of two notes sufficiently far apart, compute a valid
134 ;;; beaming. First reflect the positions vertically and horizontally
135 ;;; until the last note is higher than the first and the stems are up.
136 ;;; Then compute a valid beaming using only the first and last
137 ;;; elements of the list. Finally, move the beaming up vertically
138 ;;; until each stem it as least 2.5 staff steps long.