Re: Proper Understanding of Y-extent sought

[Janek Warchoł]

On Sun, Apr 15, 2012 at 3:14 PM, Frank Steinmetzger <address@hidden> wrote:
> Dear list
>
> Preface (go down for actual question):
> ---------------------------------------
> I am still struggling with moving my dynamics around.  I want to get rid of
> all those extra-offsets, after you told me that it’s the wrong approach.  So I
> dug into the docs and lsr again, and found out about setting Y-extent so that
> lilypond thinks that the dynamic mark takes up no vertical space.
>
> However, that’s overshooting the target.  All I’m trying to achieve is to move
> the mark around and then let lilypond do the layouting again.  The goal is to
> minimise the staff’s extent by putting dynamic marks next to its note, so they
> don’t push out the lyrics so much.

Since half a year i'm thinking about adding this to LilyPond.  Eh...

> Actual question:
> ---------------------------------------
> So instead of hoping to find a snippet on the interwebs for each single case
> and playing with the numbers without knowing why they behave as they do, I
> would like to understand what they actually mean.  All the IR says about
> Y-extent is "hardcoded extent in Y direction".
>
> So what exactly do those two numbers denote?
> Is it minimum/maximum?  Extent below/above baseline?  Offset/size?

Y-extent is vertical size of the object. Take treble clef for example:
it's "reference point" is the middle of the main loop (on 2nd staff
line counting from the bottom).  It's Y-extent is something like
'(-2.5 . 4.5) meaning that it's bottom is 2.5 staffspace below that
reference point and it's top is 4.5 ss above it.
Y-offset is the distance between object's reference point and the
reference point to which it is attached, and it doesn't have to be 0
by default.  Compile these examples:
{ \override Staff.Clef #'Y-offset = #1  a'4 }
{ \override Staff.Clef #'Y-offset = #0  a'4 }
{ \override Staff.Clef #'Y-offset = #-1  a'4 }
As you can see, Y-offset = -1 gives the normal vertical position of
treble clef.  We can deduce from this that the reference point from
which the distance is measured is middle staff line.

> PS.: Is it correct that the stems of Elias’s tied halves are so long?

Yes.
However, after the cue notes end, the font-size is wrong (it's too small).

hope this helps,
Janek