Re: Doc: NR 4.1.2: Reorganize vertical dimensions. (issue2316042)

[markpolesky]

On 2010/10/02 16:32:06, Carl wrote:
> When laying out a page, LilyPond makes a stack of the
> layout items (staves, lyrics lines, chordnames, etc.)
> on the page, with a variable spacing item between each
> pair of layout items.  When calculating the desired
> location of each layout item, the code treats the page
> as if the layout items were rigid blocks and the
> spacing items were springs, and the whole assembly of
> blocks and springs is made to fit in the space of the
> page.  In order to make it fit, the springs will be
> stretched or compressed.

> The spacing variables affect the size and strength of
> the springs, as well as the size of the rigid blocks.
> 'padding is added to the rigid block above.  'space
> determines the size of the spring -- it's the space
> that would be used if no squeezing or stretching would
> be required to fit the systems together.
> 'stretchability determines the strengths of the
> springs.  Higher values of 'stretchability make the
> spring weaker; lower values of stretchability make the
> spring stronger.  'minimum-space is the
> shortest-possible length of the spring.  When the
> space between the two layout items reaches
> 'minimum-space, the two layout items can be placed no
> closer together.

I like this a lot.  But I think it's misleading to say
that 'padding is added to the "rigid block" above,
because this implies that 'space is measured from the
bottom of the 'padding block, whereas 'space should be
measured (IIUC) from what I called the "reference
point" of the upper item, and when the upper item is a
title or markup, that reference point is the lowest
point of the title/markup.  So at least in that case,
the upper Y-coordinates of 'padding and 'space would
be the same.  Is that right?

These 2 paragraphs still leave 'stretchability somewhat
abstract, but this other line from Carl so far is the
most promising explanation:

penalty = [(proposed actual space) - (space)]/stretchability

I think we're a lot closer to a suitable explanation.
We still need to go through and agree what the most
natural "reference points" are, and then make sure the
code agrees with that.

- Mark

http://codereview.appspot.com/2316042/