Hi Mike, On Thu, Jul 22, 2010 at 7:24 AM, Mike Solomon <mike...@ufl.edu> wrote:
> Hey all, > I'm almost finished w/ a vector-graphic-spanner project I've been > working on in Lilypond (that I'm planning on using during the International > Composers Pyramid in Kent tomorrow...crosses fingers...), and to make it > work 100%, I have to make it so that the Y-extent of the spanner is > correctly taken into account every time the spanner breaks lines. The > problem is that sometimes this extent is factored into the layout, and > sometimes it is disregarded. You can see this on: > > http://www.apollinemike.com/lilypond/vector1.pdf > http://www.apollinemike.com/lilypond/vector5.pdf > > As the amount of code I've produced to make this happen is too big to > meaningfully summarize in an email, I'd rather solicit your help by asking: > how are spanners' (or just grobs' in general) y-extents found and taken > into > account in the layout process? Is there one place where lilypond's > vertically-oriented engraver(s) consult(s) grobs/spanners to find their > heights, and if so, where? That depends on the Y-parent of your grob. If it is a VerticalAlignment, then you should look at Align_interface to see how children of VerticalAlignment are laid out. Otherwise, the Y-offset property of your grob is very important, since it gives the offset between your grob and its Y-parent. How the Y-extent affects the layout depends on what Y-offset is. That is, there are some callbacks for Y-offset that depend on the extent and there are others that don't. > For example, how does lilypond know to take a > hairpin's height into account for every staff over which said hairpin is > split? We split the hairpin into multiple hairpins, one for each staff. See Spanner::do_break_processing. > I see some candidates in the source code, but not knowing how any of > them really work, I'm not sure if any of the following are promising leads: > > 1) pure-height: if I created a callback with the correct extent, would that > do anything? > Pure height is used to doing page breaking, but not for the actual layout. > 2) axis-group-interface: I am currently not using this interface. Should I > be? Does that help the correct heights to be factored into the layout? > Probably not, Y-offset is more important. > 3) are there multiple grob parameters that, when set in conjunction, sorta > cancel each other out and make lilypond disregard the Y-extent? > 4) the unknown... > > Currently, a slew of pacifier prints using `format' confirm that I'm using > the correct extents for the stencil and that the 'Y-extent property is > always correct when the print statement is called. Furthermore, when I > print the grob properties (via ly:grob-properties) to the command line, the > correctly and incorrectly laid-out grobs all have the same properties. So, > it's hard for me to track down the source of this inconsistent behavior. > Any thoughts would be appreciated! > The current extent and offsets aren't actually stored in ly:grob-properties. For performance reasons, they are in grob->dim_cache_ (only accessible from C++). Cheers, Joe
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