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Re: Auto-beam in 2.6

From: Joe Neeman
Subject: Re: Auto-beam in 2.6
Date: Tue, 05 Jul 2005 00:15:31 +1000
User-agent: Mozilla Thunderbird 1.0.2 (X11/20050402)

Stephen wrote:

> I believe revert- works like every other revert and only reverts a
> previous override, restoring the default, not reverting the default
> itself. After all, revert means to go back to a previous state, not to
> establish a state.

I think the confusing thing here (for me at least) was that, in some
cases, revert-* appears to the user to change the settings in a way that
wasn't overridden. For example, if I have
#(revert-auto-beam-setting '(end 1 16 4 4) 1 8)
a16 a a a

Then the revert-auto-beam-setting is changing the behaviour /without me
having initially overridden it/. Of course, it was initially overridden
in auto-beam.scm but that isn't obvious to the user.

The other thing that I found confusing is the use of wildcards. For example,
#(override-auto-beam-setting '(end * * * *) 1 8)
#(revert-auto-beam-setting '(end 1 16 4 4) 1 8)
doesn't work as I would have expected it.

Anyway, I wrote this thing up yesterday. I think it explains changing
the auto-beam behaviour better than the current page does. You'll notice
that I skip over any description of beam beginnings. That's because I
don't understand it yet :P

Anyway, let me know what you think.


In normal time signatures, automatic beams can start on any note but
can only end in a few positions within the measure: beams can end on a beat,
or at durations specified by the properties in autoBeamSettings.
The properties in autoBeamSettings consist of a list of rules for where
can begin and end.
The default autoBeamSettings rules are defined in scm/auto-beam.scm.

In order to add a rule to the list, use
#(override-auto-beam-setting '(be p q n m) a b [context])

 - be is either "begin" or "end"
 - p/q is the duration of the note for which you want to add a rule. A
beam is
   considered to have the duration of its shortest note. Set p and q to
'*' to
   have this apply to any beam.
 - n/m is the position in the time signature to which this rule should
   Set n and m to '*' to have this apply in any time signature.
 - a/b is the position in the bar at which the beam should end.
 - context is optional, and it specifies the context at which the change
   should be made. The default is 'Voice.
   #(score-override-auto-beam-setting '(A B C D) E F) is equivalent to
   #(override-auto-beam-setting '(A B C D) E F 'Score).

For example, if automatic beams should always end on the first quarter node,
#(override-auto-beam-setting '(end * * * *) 1 4)

You can force the beam settings to only take effect on beams whose shortest
note is a certain duration:

\time 2/4
#(override-auto-beam-setting '(end 1 16 * *) 1 16)
a16 a a a a a a a |
a32 a a a a16 a a a a a |
#(override-auto-beam-setting '(end 1 32 * *) 1 16)
a32 a a a a16 a a a a a |

You can force the beam settings to only take effect in certain time

\time 5/8
#(override-auto-beam-setting '(end * * 5 8) 2 8)
c8 c d d d
\time 4/4
e8 e f f e e d d
\time 5/8
c8 c d d d

You can also remove a previously set beam-ending rule by using
#(revert-auto-beam-setting '(be p q n m) a b [context])

be, p, q, n, m, a, b and context are the same as above. Note that the
rules are specified in scm/auto-beam.scm so you can revert rules that you
didn't explicitly create.

\time 4/4
a16 a a a a a a a a a a a a a a a
#(revert-auto-beam-setting '(end 1 16 4 4) 1 4)
a16 a a a a a a a a a a a a a a a

The rule in a revert-auto-beam-setting statement must exactly match the
original rule.
That is, no wildcard expansion is taken into account.

\time 1/4
#(override-auto-beam-setting '(end 1 16 1 4) 1 8)
a16 a a a
#(revert-auto-beam-setting '(end 1 16 * *) 1 8) % this won't revert it!
a a a a
#(revert-auto-beam-setting '(end 1 16 1 4) 1 8) % this will
a a a a

You can turn off automatic beaming altogether with \autoBeamOff.

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