Re: More questions on beam properties

[Paul]

Hi Andrew,

On 07/15/2016 10:48 AM, Andrew Bernard wrote:

What does the property Beam.positions actually represent? I have seen code that treats it as the y position coordinates of the end points of the beam, but I cannot make sense of this. Nor can I make sense of the manual page for Beam, which gives, as far as I can see, negative information! -

positions (pair of numbers):

beam::place-broken-parts-individually

Pair of staff coordinates (left . right), where both left and right are in staff-space units of the current staff. For slurs, this value selects which slur candidate to use; if extreme positions are requested, the closest one is taken.

How anybody can read that and understand what it says about beams is somewhat beyond me. This makes it difficult to program with the properties in question.

One factor is that the doc strings for these properties are not specific to one grob.  The positions property is (re-)used for many grobs and so the doc string is very general and often doesn't speak to their use by particular grobs.  The mention of slurs is because of this.

What on earth is ‘beam::place-broken-parts-individually’ in the context of beam start end vertical positioning? Dear me.

It's a callback function that is called to calculate the value of that property for this grob.  So you have to look at the code in this case to learn more. 

Maybe that helps explain what's going on with the documentation at least.

-Paul