Re: Create different pdf layers

[Jan-Peter Voigt]

Hi Urs,

isn't the layer grob property what you want?
This is what I use to interrupt ties (or slurs) if they collide with a 
time signature:
% to have the time sig behind the staff symbol
\override Staff.TimeSignature #'layer = #-5
% whiteout anything behind the time sig
\override Staff.TimeSignature #'whiteout = ##t
% ties are behind the time sig
\override Tie #'layer = #-10

Now you can listen for the grob-interface and look, if its set to a 
specific number and then do anything whith the grob (color it or set the 
stencil to #f)
The layer may be a procedure, so it may be set conditionally by some 
other method.

Best, Jan-Peter

On 01.08.2013 10:15, Urs Liska wrote:
> I have brought this up before without success. But as my interest 
> reappeared I'll try it again with a slightly more specific question.
>
> When LilyPond finally renders its objects 'on paper' how complicated 
> would it be to allow it to print on layers that show up as separate 
> layers in the final pdf?
> I would consider this a very useful enhancement.
>
> As a first step this could and should be done without any layout 
> considerations, i.e. without changing anything in the layout engine. 
> Simply put grobs on the default or a dedicated layer with a syntax 
> something like
>
> \new Layer = "Annotations"
> \change Layer = "Annotations"
> \change Layer = "Default"
>
> Instead of the \new Layer command I also could imagine defining layers 
> in the \paper block
>
> There is much more potential in this, but just to show what I mean 
> (with a known construct):
> If I could print the result of annotate-spacing on a different layer I 
> could simply switch that layer on and off in a pdf viewer.
> Or if I have layout-indifferent additions like the control-points 
> visualization in
> http://lilypondblog.org/wp-content/uploads/2013/07/chopin-beams-5.preview.png 
>
> it would be nice to be able to switch them on and off without having 
> to recompile the file.
>
> Any ideas?
>
> Urs
>
> PS: As a first step it already would be nice to know
> - where (in the code) LilyPond actually 'prints' its objects (and 
> where to)
> - where I can find concise and understandable information about how 
> PDF layers are created
>   (in the sense of creating them when writing a file, not how to 
> create them in Acrobat or the like)
>
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