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Re: music function to be included somewhere in scm/*

From: Alexander Kobel
Subject: Re: music function to be included somewhere in scm/*
Date: Fri, 16 Dec 2016 17:38:57 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.4.0

Hi Paul.

On 2016-12-16 16:02, Paul wrote:
Hi Knut and everyone,

Great to see your work which seems like a nice improvement.  I just have
some thoughts on the implementation / use of properties.

We are just talking about grob properties and not context properties
right?  In that case no need to also create context properties as you do
in your patch, since the grob properties are sufficient.

Yes, I think that's a general agreement now. AFAICS, the idea of context properties quickly vanished after we recognized that we can get rid of __ (or ExtenderEvents) entirely, at least as far as the user is concerned. They are now more like an implementation detail for no-extender.

What about a way to do this with fewer than 3 separate grob properties?


If I understand correctly, only 1 of 3 kinds of behavior can be in
effect at a given point:

1. no extensions
2. forced extensions
3. automatically added extension depending on a 'minimum-length' number

Not quite. I can imagine that no-extender and force-extender could be combined. E.g., as create-extender = { one of #'auto, #'never, #'always }:

#'auto means the default: create extenders on melismata and nowhere else.
#'never means: create no extenders, period.
#'always means that extenders are enforced even on non-melismata (where, by definition, there should not be an extender; but there are situations where it makes sense to overwrite it; e.g., for a continuation of an extender in a second volta repeat, or in divisi lyrics).

Minimum-length [2] is orthogonal - it is more concerned with the layout. With some reasonable minimum-length, extenders that reduce to mere flyspecks are hidden. This happens often in somewhat dense choral settings: the extender is not printed if the syllable text is almost as wide (or even wider) than the distance between the respective noteheads. It's a threshold value that tells which existing extenders will be printed and visible. [1] But this decision entirely depends on horizontal spacing, and will vary with line breaks, other voices, etc. IMHO, that's a whole different quality of a variable than the previous one (existence vs. appearance). And the general design principle throughout Lilypond is to separate semantics from layout as much as possible.

[1] One exception: on forced extenders on non-melismata (which do not have any natural length, obviously), minimum-length will not serve as a threshold, but to /set/ the length.

[2] Side Note: other proposed names for minimum-length so far:

(1) minimum-space
(2) show-length
(3) hide-below-length
(4) hide-if-shorter-than
(5) minimum-visibility
(6) visibility-threshold
(7) printing-threshold
(8) extender-threshold

So why not one grob property (name to be determined) that can be a
boolean or a number:

LyricExtender.extenders = ##f   % no extensions
LyricExtender.extenders = ##t   % forced extensions
LyricExtender.extenders = 2        % a number, auto extensions

For example, it could be set to a number and then use \once to set it to
##t to force (or ##f to suppress) a given extender.

See [1] above; we need to be able to specify a length for forced extenders (that do not have a natural length because there's only one note). Yes, something like extenders = #'(forced? length) with a boolean for forced? and a number for length would be sufficient (note that #'(#f +inf.0) amounts to #'never...), but that's quite opaque.

Another possibility (2 properties) might be:

LyricExtender.stencil = ##f                % no extensions
LyricExtender.force-extender = ##t  % forced extensions
LyricExtender.minimum-length = 2    % auto extensions (if force-extender
is not ##t and stencil is not ##f)

Yes, that'll work: stencil = ##f means #'never; stencil = ##t and force-extender = ##t means #'always; and stencil = ##t and force-extender = ##f means #'auto. However, I personally dislike to touch stencil. That's my last resort, but it feels hacky; IMHO stencil is a more or less internal layout procedure, and I should not have to abuse it for semantic purposes (i.e., #'never).


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