The headings reflect questions from Doug or comments from Han-Wen;
the body text are Han-Wen's answers.
-@subsubsection Figuring out how things work.
+@unnumberedsubsubsec Figuring out how things work.
I must admit that when I want to know how a program works, I use grep
and emacs and dive into the source code. The comments and the code
itself are usually more revealing than technical documents.
-@subsubsection What's a grob, and how is one used?
+@unnumberedsubsubsec What's a grob, and how is one used?
Graphical object - they are created from within engravers, either as
Spanners (derived class) -slurs, beams- or Items (also a derived
contains all items that happen at the same moment). They are separate
classes because they play a special role in the linebreaking process.
-@subsubsection What's a smob, and how is one used?
+@unnumberedsubsubsec What's a smob, and how is one used?
A C(++) object that is encapsulated so it can be used as a Scheme
object. See GUILE info, "19.3 Defining New Types (Smobs)"
-@subsubsection When is each C++ class constructed and used
+@unnumberedsubsubsec When is each C++ class constructed and used
@itemize
@end itemize
-@subsubsection Can you get to Context properties from a Music object?
+@unnumberedsubsubsec Can you get to Context properties from a Music object?
You can create music object with a Scheme function that reads context
properties (the \applycontext syntax). However, that function is
properties from Music objects, since music objects are not directly
connected to Contexts. That connection is made by the Music_iterators
-@subsubsection Can you get to Music properties from a Context object?
+@unnumberedsubsubsec Can you get to Music properties from a Context object?
Yes, if you are given the music object within a Context
object. Normally, the music objects enter Contexts in synchronized
fashion, and the synchronization is done by Music_iterators.
-@subsubsection What is the relationship between C++ classes and Scheme objects?
+@unnumberedsubsubsec What is the relationship between C++ classes and Scheme objects?
Smobs are C++ objects in Scheme. Scheme objects (lists, functions) are
manipulated from C++ as well using the GUILE C function interface
(prefix: scm_)
-@subsubsection How do Scheme procedures get called from C++ functions?
+@unnumberedsubsubsec How do Scheme procedures get called from C++ functions?
scm_call_*, where * is an integer from 0 to 4.
Also scm_c_eval_string (), scm_eval ()
-@subsubsection How do C++ functions get called from Scheme procedures?
+@unnumberedsubsubsec How do C++ functions get called from Scheme procedures?
Export a C++ function to Scheme with LY_DEFINE.
-@subsubsection What is the flow of control in the program?
+@unnumberedsubsubsec What is the flow of control in the program?
Good question. Things used to be clear-cut, but we have Scheme
and SMOBs now, which means that interactions do not follow a very
rigid format anymore. See below for an overview, though.
-@subsubsection Does the parser make Scheme procedure calls or C++ function
-calls?
+@unnumberedsubsubsec Does the parser make Scheme procedure calls or C++ function calls?
Both. And the Scheme calls can call C++ and vice versa. It's nested,
with the SCM datatype as lubrication between the interactions
(I think the word "lubrication" describes the process better than the
traditional word "glue")
-@subsubsection How do the front-end and back-end get started?
+@unnumberedsubsubsec How do the front-end and back-end get started?
Front-end: a file is parsed, the rest follows from that. Specifically,
Paper_lines and other things. This area is still heavily in flux, and
perhaps not something you should want to look at.
-@subsubsection How do the front-end and back-end communicate?
+@unnumberedsubsubsec How do the front-end and back-end communicate?
There is no communication from backend to front-end. From front-end to
backend is simply the program flow: music + definitions gives
contexts, contexts yield output, after processing, output is written
to disk.
-@subsubsection Where is the functionality associated with KEYWORDs?
+@unnumberedsubsubsec Where is the functionality associated with KEYWORDs?
See my-lily-lexer.cc (keywords, there aren't that many) and ly/*.ly
(most of the other backslashed \words are identifiers)
-@subsubsection What Contexts/Properties/Music/etc. are available when they are processed?
+@unnumberedsubsubsec What Contexts/Properties/Music/etc. are available when they are processed?
What do you mean exactly with this question?
See ly/engraver-init.ly for contexts, see scm/define-*.scm for other
objects.
-@subsubsection How do you decide if something is a Music, Context, or Grob property?
+@unnumberedsubsubsec How do you decide if something is a Music, Context, or Grob property?
Why is part-combine-status a Music property when it seems (IMO)
to be related to the Staff context?
Part_combine_iterator to communicate with Part_combine_engraver.
-@subsubsection I'm adding a property to affect how \autochange works. It seems to
+@unnumberedsubsubsec I'm adding a property to affect how \autochange works. It seems to
me that it should be a context property, but the Scheme autochange
procecure has a Music argument. Does this mean I should use
a Music property?
where around-central-C is some function that is called from
make-autochange-music.
-@subsubsection Also, I get lost figuring out what environment the code I'm looking at is in
-when it executes. I found both the C++ and Scheme autochange code. Then I was
+@unnumberedsubsubsec I get lost figuring out what environment the code I'm looking at is in when it executes.
+I found both the C++ and Scheme autochange code. Then I was
trying to figure out where the code got called from. I finally figured out that
the Scheme procedure was called before the C++ iterator code, but it took me a
while to figure that out, and I still didn't know who did the calling in the
first place. I only know a little bit about Flex and Bison, so reading those
files helped only a little bit.
-GDB can be of help here. Set a breakpoint in C++, and run. When you
+@emph{Han-Wen:} GDB can be of help here. Set a breakpoint in C++, and run. When you
hit the breakpoint, do a backtrace. You can inspect Scheme objects
along the way by doing
projects / lilypond.git / commitdiff