correct off-by-one error on face/line indices

obj2d.rb

@@ -29,9 +29,9 @@ def main(obj_fname, d_fname)
     elsif line =~ /^o\s+(.*)/
       raise "Do not know how to handle object #{$1.inspect}"
     elsif line =~ /^f\s+(\d+)\s+(\d+)\s+(\d+)/
-      cur_obj << [$1, $2, $3].map(&:to_i)
+      cur_obj << [$1, $2, $3].map {|v| v.to_i - 1}
     elsif line =~ /^l\s+(\d+)\s+(\d+)/
-      cur_obj << [$1, $2].map(&:to_i)
+      cur_obj << [$1, $2].map {|v| v.to_i - 1}
     end
   end
   File.open(d_fname, "w") do |fh|