Add diagram generation with graphviz

* configure.ac (TWOPI, HAS_TWOPI): Add variables.
  Check for towpi.
* doc/.gitignore (diagrams/*.svg): Add output file ignore.
* doc/Makefile.am: Add svg diagram building.

configure.ac

@@ -34,6 +34,11 @@ AC_CHECK_PROGS(NODE, [node nodejs])
 
 test -n "$NODE" || AC_MSG_ERROR([missing Node.js])
 
+# graphviz
+AC_ARG_VAR([TWOPI], [Graphviz twopi layout])
+AC_CHECK_PROGS(TWOPI, [twopi])
+AM_CONDITIONAL(HAS_TWOPI, [test "$TWOPI"])
+
 # only needed for older versions of Node
 AC_MSG_CHECKING([node --harmony_destructuring])
 AS_IF([node --harmony_destructuring >/dev/null 2>/dev/null],

doc/.gitignore

@@ -13,6 +13,7 @@
 *.pdf
 *.dvi
 *.html
+diagrams/*.svg
 
 # generated by configure/autotools
 Makefile

doc/Makefile.am

@@ -21,4 +21,14 @@
 MAKEINFOHTML = $(MAKEINFO) --html --css-include liza.css
 
 info_TEXINFOS = liza.texi
-liza_TEXINFOS = design.texi macros.texi config.texi liza.css
+liza_TEXINFOS = design.texi macros.texi config.texi liza.css \
+                diagram/event-graph.svg
+
+diagram/%.svg: diagram/%.dot
+if HAS_TWOPI
+	$(TWOPI) -Tsvg "$<" > "$@"
+else
+	@echo "cannot build $<;" >&2
+	@echo "install graphviz package and re-configure" >&2
+endif
+