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	layout.txt (7123B)
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	1
	2
	3 How the notes are arranged on the staff in abc2ps
	4 =================================================
	5
	6 This file contains more detailed information on the way in which
	7 the layout is calculated in abc2ps, for those who are interested
	8 or would like to change the layout.
	9
	10
	11 ----- General points -----
	12
	13 When typesetting music, an important feature is presumably
	14 that notes and rests are arranged in some way which indicates
	15 the note durations. The following considerations entered
	16 into abc2ps:
	17
	18 (a) The space assigned a note should be qualitatively proportional
	19 to its durations, but this mapping should not be strictly linear.
	20 It seems best to "saturate" the mapping so that whole notes
	21 are somewhat less than twice as wide as half notes. At the other
	22 end, the width allocated to 8th and 16th notes must be
	23 more similar than a factor of 1/2 or the layout looks uneven.
	24 Thus, for durations approaching zero the note width should go
	25 to some constant. A modifiable function nwidth(len) defines
	26 the mapping.
	27
	28 (b) Given a sequence of notes (or rests) within a bar, the space
	29 between any two should reflect the duration of the first.
	30 If this is done strictly, the distance along the staff becomes
	31 the correct "time axis" but the output looks uneven.
	32 Therefore there is an "asymmetry" parameter beta to adjust.
	33 For beta=0, the internote spacing comes equally from both neighbor
	34 notes, and for beta=1 only the first note of each pair is taken
	35 into account.
	36
	37 (c) When notes are grouped under a beam, they are moved slightly
	38 closer together.
	39
	40 (d) The spacing between a note at the start of a measure and the
	41 preceding bar line is a separate case. On the one hand, the duration
	42 of the note could influence the spacing. On the other hand,
	43 music often seems to be written with this spacing some fixed standard
	44 distance. The treatment here is to choose a standard space (eg. some
	45 fraction of a full measure) and another tuning parameter beta. For be…
	46 the standard distance is used, and for beta=1 the space is taken from
	47 the note duration. Notes at the end of a measure are treated similari…
	48
	49 (e) If a measure has only one note in it, one can put the note exactl…
	50 into the middle and calculate the measure width from the note duratio…
	51 Alternatively, this case can be treated like case (d) as a bar-note
	52 and a note-bar case. A further parameter interpolates between these
	53 alternatives.
	54
	55
	56 ----- Puristic layout -----
	57
	58 To change the layout rules, the parameters in file "style.h" should
	59 be modified. As a starting point, it is useful to consider a strict
	60 layout defined as follows (see file "style.pure"):
	61
	62 (a) Make the mapping between note length and the space on the paper l…
	63
	64 (b) Make the space between two notes exactly proportional to the leng…
	65 of the first note.
	66
	67 (c) Do not move notes under beams closer together.
	68
	69 (d) Put notes at the start of a measure at a fixed distance behind th…
	70 Put a bar behind a note at a spacing proportional to the note len…
	71
	72 (e) Treat a measure with a single note in it like case (d).
	73
	74 For this layout, the position of each note exactly gives the time when
	75 the note starts. It looks more or less like what one wants, but it is
	76 too strict for good readability. One way to get suitable layout
	77 parameters is to start from the settings in "style.pure" and twiddle
	78 on the parameters.
	79
	80
	81 ----- Algorithm for filling out the staffs -----
	82
	83 This is similar to the procedure used by Knuth in TeX
	84 as described in the TeXBook, chapter on "Glue".
	85 Three different sets of spacings are defined: shrink, space, stretch.
	86
	87 shrink: the smallest acceptable spacings. These are controlled
	88 by function set_sym_widths().
	89 space: prefered "natural" spacings at which layout looks best.
	90 All parameters in style.h ending in 'p' are relevant.
	91 stretch: spacings for an expanded "stretched" layout.
	92 All parameters in style.h ending in 'x' are relevant.
	93
	94 To set a line, the natural spacings are added together. If the sum is
	95 larger than the desired staff length, the final spacings are obtained
	96 by linear interpolation between the "shrink" and "space" values.
	97 If the sum is smaller, the spacings are obtained by interpolating
	98 between the "space" and "stretch" values. Compression does not go
	99 beyond the "shrink" spacings but expansion is allowed to any width.
	100 (Formal note: the definition of shrink and stretch used here is not
	101 the same as in TeX; eg. the minimal spacing is here 'shrink'
	102 whereas in TeX it is 'space-shrink'.)
	103
	104
	105 ----- How to proceed when changing the layout -----
	106
	107 When changing the output appearance, the important thing is to modify
	108 the three glue modes "shrink", "space", and "stretch" separately.
	109 Since a typical music line is a mixture of these modes, it is
	110 difficult to see what is happening when changing the parameters
	111 in the "fill" mode. In detail:
	112
	113 (1) Use info field 'E:shrink' or the flag "-g shrink" to force
	114 maximally compressed output. In this mode, no extra glue is put
	115 between the symbols. The layout should be as compressed as possible
	116 while still being acceptable. The spacings are here given by
	117 the left and right widths wl,wr which are defined in routine
	118 set_sym_widths(). These are presently set so that symbols
	119 have a small space around them, taking into account dots, flags,
	120 accidentals etc. Slightly more space is left around open notes and
	121 fat bars.
	122
	123 (2) Next, use 'E:space' or "-g space" to force the prefered natural
	124 spacing. This layout should be adjusted to get the ouput which looks
	125 best. As in case (1), there are left and right widths for each symbol,
	126 now called pl and pr, which are also set in set_sym_widths().
	127 The important difference is that spacings around notes and rests
	128 are influenced by the durations. This is done according
	129 to the rules described above, using the parameters ending in 'p'
	130 in style.h. The relevant routine is set_sym_poslist().
	131
	132 (3) Finally, use 'E:stretch' to force stretched output.
	133 This output should be something like twice as wide but should still b…
	134 easily readable. For example, this implies that internote spacings ar…
	135 more even than in the "space" mode. Internally, the stretched spacing…
	136 are calculated exactly as the prefered spacings, using left and right
	137 widths xl and xr, function xwidth(len), and the parameters ending
	138 in 'x' in style.h.
	139
	140 The idea is that after obtaining satisfactory layouts for the shrink,
	141 space, and stretch modes separately, the output should look good
	142 when the spacings are interpolated to fill out the staff.
	143
	144 If you change the style file to your tastes, you might as well
	145 give the layout a new name, by changing the macro STYLE in style.h.
	146 This is so that the command 'abc2ps -V' can show what style is
	147 currently being used.
	148
	149
	150 Michael Methfessel, Feb 1996.