Add cornell scene

This includes a bunch of variants on the standard cornell box, uploaded at https://github.com/jvm-graphics-labs/awesome-3d-meshes/tree/master/McGuire. I had to add a hack to the obj loader to start supporting reflective surfaces.

scenes/cornell.cry

@@ -0,0 +1,33 @@
+{
+    num_samples: 16,
+    max_depth: 8,
+    camera: Perspective {
+        origin: Point(0, 1, -2.8),
+        target: Point(0, 1, 0),
+        up: Vector(0, 1, 0),
+        fov: 60,
+        film: {
+            width: 400,
+            height: 400,
+        }
+    },
+    lights: [
+    ],
+    materials: {
+        default: Matte { reflectance: Color(1, 1, 1), sigma: 0 }
+    },
+    shapes: {
+    },
+    primitives: [
+        // Source: https://github.com/jvm-graphics-labs/awesome-3d-meshes/
+        Mesh { file_name: 'objs/local/cornell/CornellBox-Original.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Sphere.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Empty-CO.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Empty-RG.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Empty-White.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Glossy-Floor.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Glossy.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Mirror.obj', fallback_material: 'default' },
+        // Mesh { file_name: 'objs/local/cornell/CornellBox-Water.obj', fallback_material: 'default' },
+    ]
+}

src/obj.rs

@@ -74,7 +74,12 @@ pub fn load_obj(file_name: &str, fallback_material: Arc<Material>) -> Vec<Arc<Pr
             let eta = m.optical_density.unwrap_or(1.0);
             Arc::new(Material::new_glass(reflectance, transmittance, eta))
         } else {
-            Arc::new(Material::new_plastic(diffuse, specular, roughness))
+            // This is a hacky way to support reflective surfaces. We should
+            // likely switch to glTF or something
+            match m.illumination_model {
+                Some(3 | 4 | 5 | 6 | 7 | 8 | 9) => Arc::new(Material::new_metal(diffuse, specular)),
+                _ => Arc::new(Material::new_plastic(diffuse, specular, roughness)),
+            }
         };
         debug!("\t{:?}", material);
         materials.push(material);