On 6/1/10 1:26 AM, "David Kastrup" <d...@gnu.org> wrote: > Carl Sorensen <c_soren...@byu.edu> writes: > > Properties. There are tweaks, overrides, sets. Some of them work on > some properties, and there is no user level coherence to what you need > to do on what and why. Yes, I had some fits about that already, and > some people repeatedly told me I am an awful child for keeping up the > "why, why" questions and that things were just so. But I am arrogant > enough to say that something that can't be explained to me in a way that > I understand it is a mistake in a programmer interface. And we are > talking about a _user_ interface, one you can't avoid using.
I can't answer the *why* question, but I can answer the what: 1) \set: Used to apply a setting that belongs to a context, and will in general affect all grobs in the context. \set properties agre generally established once per piece, and define how the context will respond throughout the piece. 2) \override: Used to modify the settings for a type of grob, to change the default behavior in the context. \override values apply to all grobs at a given moment in the named context. \override can apply from this time forward, or can be used with \once to apply only at a given time interval. 3) \tweak: Used to modify the appearance of a particular grob. This is used when \override won't work, because we don't want to affect all the grobs at that time step. Now, as to *why* we can't \override context properties, I don't know. I don't know if this is strictly a design decision, or if it's a technical limitation of some kind (although I can't imagine why it would be so). I suspect that discussions about this topic constitute bikeshedding. I suspect that patches that allowed \override to be applied to context properties might be accepted. As I wrote the previous paragraph, I think I finally got some clarity. The way \override is currently implemented is that a copy of the alist is made, and then the new property is prepended, and the new alist is prepended to the old alist-chain. So if we were \overriding context properties, we'd have very large alist-chains hanging around unnecessarily. Also, \set works on a hash-table (which is how context properties are stored) and \override works on an alist-chain (which is how grob properties are stored). The user shouldn't have to know these details, but that may be part of the why. I hope this has been a bit helpful, Carl _______________________________________________ lilypond-devel mailing list lilypond-devel@gnu.org http://lists.gnu.org/mailman/listinfo/lilypond-devel
