lib/rgl/dot.rb in rgl-0.5.2 vs lib/rgl/dot.rb in rgl-0.5.3

@@ -3,10 +3,13 @@
 # $Id$
 #
 # Minimal Dot support, based on Dave Thomas's dot module (included in rdoc).
 # rdot.rb is a modified version which also contains support for undirected
 # graphs.
+#
+# You need to have [GraphViz](http://www.graphviz.org) installed, because the
+# functions in this modul execute the GraphViz executables _dot_ or _dotty_.
 
 require 'rgl/rdot'
 
 module RGL
 
@@ -62,11 +65,13 @@
     def dotty(params = {})
       dotfile = "graph.dot"
       File.open(dotfile, "w") do |f|
         print_dotted_on(params, f)
       end
-      system("dotty", dotfile)
+      unless system("dotty", dotfile)
+        raise "Error executing dotty. Did you install GraphViz?"
+      end
     end
 
     # Use dot[http://www.graphviz.org] to create a graphical representation of
     # the graph. Returns the filename of the graphics file.
     #
@@ -76,10 +81,12 @@
 
       File.open(src, 'w') do |f|
         f << self.to_dot_graph.to_s << "\n"
       end
 
-      system("dot -T#{fmt} #{src} -o #{dot}")
+      unless system("dot -T#{fmt} #{src} -o #{dot}")
+        raise "Error executing dot. Did you install GraphViz?"
+      end
       dot
     end
 
   end # module Graph