public Stream Generate(string dotSource, LayoutEngine engine, OutputFormat fmt)
{
var res = processRunner.Run(dotExe, new MemoryStream(Encoding.ASCII.GetBytes(dotSource)), engine.AsCmdLineParam(), fmt.AsCmdLineParam());
if (res.ExitCode!=0)
throw new Exception(
string.Format("Process [{4}] finished with non-zero code:[{0}] \nwhile generating data format: [{1}] using layout engine: [{2}]\nsrc={3}",
res.ExitCode, fmt, engine, dotSource.Shorter(), dotExe));
return res.StdOut;
}