rtiow: add dragon scene, tune stltest to compare with cuboid.

Refactor enum Model to use strum.

rtiow/tracer/Cargo.toml

@@ -11,3 +11,4 @@ log = "0.4.17"
 renderer = { path = "../renderer" }
 stderrlog = "0.4.3"
 structopt = "0.2.18"
+strum = "0.24.1"

rtiow/tracer/src/main.rs

@@ -6,7 +6,8 @@ use cpuprofiler::PROFILER;
 use log::info;
 use structopt::StructOpt;
 
-use renderer::renderer::{render, Opt};
+use renderer::renderer::{render, Model, Opt};
+use strum::VariantNames;
 
 #[cfg(not(feature = "profile"))]
 struct MockTimer;
@@ -41,8 +42,12 @@ fn main() -> Result<(), std::io::Error> {
         .init()
         .unwrap();
     let opt = Opt::from_args();
+    if opt.model.is_none() {
+        eprintln!("--model should be one of {:?}", Model::VARIANTS);
+        return Ok(());
+    }
     info!("{:?}", opt);
-    let scene = opt.model.scene(&opt);
+    let scene = opt.model.as_ref().unwrap().scene(&opt);
     fs::create_dir_all(&opt.output)?;
     if opt.pprof.is_some() && !cfg!(feature = "profile") {
         panic!("profiling disabled at compile time, but -pprof specified");