Added DistantDiskLight (a.k.a. sun light) parsing and data structures.

Also created a proper World struct in the process, to store all
infinite-extent type stuff.

Note that I goofed and did a new rustfmt pass but forgot to
commit before making these changes, so there's a lot of
formatting changes in this too.  *sigh*

src/algorithm.rs

@@ -191,8 +191,9 @@ pub fn merge_slices_to<T: Lerp + Copy, F>(slice1: &[T],
     if slice1.len() == 0 || slice2.len() == 0 {
         return;
     } else if slice1.len() == slice2.len() {
-        for (xfo, (xf1, xf2)) in Iterator::zip(slice_out.iter_mut(),
+        for (xfo, (xf1, xf2)) in
-                                               Iterator::zip(slice1.iter(), slice2.iter())) {
+            Iterator::zip(slice_out.iter_mut(),
+                          Iterator::zip(slice1.iter(), slice2.iter())) {
             *xfo = merge(xf1, xf2);
         }
     } else if slice1.len() > slice2.len() {
@@ -216,14 +217,12 @@ mod tests {
     use super::*;
 
     fn quick_select_ints(list: &mut [i32], i: usize) {
-        quick_select(list, i, |a, b| {
+        quick_select(list, i, |a, b| if a < b {
-            if a < b {
+            Ordering::Less
-                Ordering::Less
+        } else if a == b {
-            } else if a == b {
+            Ordering::Equal
-                Ordering::Equal
+        } else {
-            } else {
+            Ordering::Greater
-                Ordering::Greater
-            }
         });
     }
 

src/assembly.rs

@@ -48,13 +48,14 @@ impl Assembly {
             } else {
                 Matrix4x4::new()
             };
-            if let Some((light_i, sel_pdf, whittled_n)) = self.light_accel
+            if let Some((light_i, sel_pdf, whittled_n)) =
-                .select(incoming * sel_xform,
+                self.light_accel
-                        pos * sel_xform,
+                    .select(incoming * sel_xform,
-                        nor * sel_xform,
+                            pos * sel_xform,
-                        closure.as_surface_closure(),
+                            nor * sel_xform,
-                        time,
+                            closure.as_surface_closure(),
-                        n) {
+                            time,
+                            n) {
                 let inst = self.light_instances[light_i];
                 match inst.instance_type {
 
@@ -239,19 +240,17 @@ impl AssemblyBuilder {
         // sources.
         let mut light_instances: Vec<_> = self.instances
             .iter()
-            .filter(|inst| {
+            .filter(|inst| match inst.instance_type {
-                match inst.instance_type {
+                InstanceType::Object => {
-                    InstanceType::Object => {
+                    if let Object::Light(_) = self.objects[inst.data_index] {
-                        if let Object::Light(_) = self.objects[inst.data_index] {
+                        true
-                            true
+                    } else {
-                        } else {
+                        false
-                            false
-                        }
                     }
+                }
 
-                    InstanceType::Assembly => {
+                InstanceType::Assembly => {
-                        self.assemblies[inst.data_index].light_accel.approximate_energy() > 0.0
+                    self.assemblies[inst.data_index].light_accel.approximate_energy() > 0.0
-                    }
                 }
             })
             .map(|&a| a)

src/light/distant_disk_light.rs

@@ -0,0 +1,82 @@
+use std::f64::consts::PI as PI_64;
+
+use color::{XYZ, SpectralSample, Color};
+use lerp::lerp_slice;
+use math::{Vector, coordinate_system_from_vector};
+use sampling::{uniform_sample_cone, uniform_sample_cone_pdf};
+
+use super::WorldLightSource;
+
+// TODO: handle case where radius = 0.0.
+
+#[derive(Debug)]
+pub struct DistantDiskLight {
+    radii: Vec<f32>,
+    directions: Vec<Vector>,
+    colors: Vec<XYZ>,
+}
+
+impl DistantDiskLight {
+    pub fn new(radii: Vec<f32>, directions: Vec<Vector>, colors: Vec<XYZ>) -> DistantDiskLight {
+        DistantDiskLight {
+            radii: radii,
+            directions: directions,
+            colors: colors,
+        }
+    }
+}
+
+impl WorldLightSource for DistantDiskLight {
+    fn sample(&self, u: f32, v: f32, wavelength: f32, time: f32) -> (SpectralSample, Vector, f32) {
+        // Calculate time interpolated values
+        let radius: f64 = lerp_slice(&self.radii, time) as f64;
+        let direction = lerp_slice(&self.directions, time);
+        let col = lerp_slice(&self.colors, time);
+        let solid_angle_inv = 1.0 / (2.0 * PI_64 * (1.0 - radius.cos()));
+
+        // Create a coordinate system from the vector pointing at the center of
+        // of the light.
+        let (z, x, y) = coordinate_system_from_vector(-direction);
+        let (x, y, z) = (x.normalized(), y.normalized(), z.normalized());
+
+        // Calculate the radius in terms of cosine
+        let cos_theta_max: f64 = radius.cos();
+
+        // Sample the cone subtended by the light.
+        let sample = uniform_sample_cone(u, v, cos_theta_max).normalized();
+
+        // Calculate the final values and return everything.
+        let shadow_vec = (x * sample.x()) + (y * sample.y()) + (z * sample.z());
+        let pdf = uniform_sample_cone_pdf(cos_theta_max);
+        let spectral_sample = (col * solid_angle_inv as f32).to_spectral_sample(wavelength);
+        return (spectral_sample, shadow_vec, pdf as f32);
+    }
+
+    fn sample_pdf(&self, sample_dir: Vector, wavelength: f32, time: f32) -> f32 {
+        // We're not using these, silence warnings
+        let _ = (sample_dir, wavelength);
+
+        let radius: f64 = lerp_slice(&self.radii, time) as f64;
+        return uniform_sample_cone_pdf(radius.cos()) as f32;
+    }
+
+    fn outgoing(&self, dir: Vector, wavelength: f32, time: f32) -> SpectralSample {
+        // We're not using this, silence warning
+        let _ = dir;
+
+        let radius = lerp_slice(&self.radii, time) as f64;
+        let col = lerp_slice(&self.colors, time);
+        let solid_angle = 2.0 * PI_64 * (1.0 - radius.cos());
+        (col / solid_angle as f32).to_spectral_sample(wavelength)
+    }
+
+    fn is_delta(&self) -> bool {
+        false
+    }
+
+    fn approximate_energy(&self) -> f32 {
+        let color: XYZ = self.colors.iter().fold(XYZ::new(0.0, 0.0, 0.0), |a, &b| a + b) /
+                         self.colors.len() as f32;
+        color.y
+    }
+}

src/light/mod.rs

@@ -1,3 +1,4 @@
+mod distant_disk_light;
 mod rectangle_light;
 mod sphere_light;
 
@@ -7,14 +8,17 @@ use boundable::Boundable;
 use color::SpectralSample;
 use math::{Vector, Point, Matrix4x4};
 
+pub use self::distant_disk_light::DistantDiskLight;
 pub use self::rectangle_light::RectangleLight;
 pub use self::sphere_light::SphereLight;
 
 
+/// A finite light source that can be bounded in space.
 pub trait LightSource: Boundable + Debug + Sync {
     /// Samples the light source for a given point to be illuminated.
     ///
-    ///     - arr: The point to be illuminated.
+    ///     - space: The world-to-object space transform of the light.
+    ///     - arr: The point to be illuminated (in world space).
     ///     - u: Random parameter U.
     ///     - v: Random parameter V.
     ///     - wavelength: The wavelength of light to sample at.
@@ -77,6 +81,54 @@ pub trait LightSource: Boundable + Debug + Sync {
     fn is_delta(&self) -> bool;
 
 
+    /// Returns an approximation of the total energy emitted by the light
+    /// source.  Note that this does not need to be exact: it is used for
+    /// importance sampling.
+    fn approximate_energy(&self) -> f32;
+}
+
+
+/// An infinite light source that cannot be bounded in space.  E.g.
+/// a sun light source.
+pub trait WorldLightSource: Debug + Sync {
+    /// Samples the light source for a given point to be illuminated.
+    ///
+    ///     - u: Random parameter U.
+    ///     - v: Random parameter V.
+    ///     - wavelength: The wavelength of light to sample at.
+    ///     - time: The time to sample at.
+    ///
+    /// Returns: The light arriving from the shadow-testing direction, the
+    /// vector to use for shadow testing, and the pdf of the sample.
+    fn sample(&self, u: f32, v: f32, wavelength: f32, time: f32) -> (SpectralSample, Vector, f32);
+
+
+    /// Calculates the pdf of sampling the given sample_dir.  This is used
+    /// primarily to calculate probabilities for multiple importance sampling.
+    ///
+    /// NOTE: this function CAN assume that sample_dir is a valid sample for
+    /// the light source (i.e. hits/lies on the light source).  No guarantees
+    /// are made about the correctness of the return value if it isn't valid.
+    fn sample_pdf(&self, sample_dir: Vector, wavelength: f32, time: f32) -> f32;
+
+
+    /// Returns the color emitted in the given direction from the
+    /// given parameters on the light.
+    ///
+    ///     - dir: The direction of the outgoing light.
+    ///     - wavelength: The hero wavelength of light to sample at.
+    ///     - time: The time to sample at.
+    fn outgoing(&self, dir: Vector, wavelength: f32, time: f32) -> SpectralSample;
+
+
+    /// Returns whether the light has a delta distribution.
+    ///
+    /// If a light has no chance of a ray hitting it through random process
+    /// then it is a delta light source.  For example, point light sources,
+    /// lights that only emit in a single direction, etc.
+    fn is_delta(&self) -> bool;
+
+
     /// Returns an approximation of the total energy emitted by the light
     /// source.  Note that this does not need to be exact: it is used for
     /// importance sampling.

src/light/sphere_light.rs

@@ -9,6 +9,7 @@ use sampling::{uniform_sample_cone, uniform_sample_cone_pdf, uniform_sample_sphe
 
 use super::LightSource;
 
+// TODO: handle case where radius = 0.0.
 
 #[derive(Debug)]
 pub struct SphereLight {
@@ -57,7 +58,7 @@ impl LightSource for SphereLight {
         // Create a coordinate system from the vector between the
         // point and the center of the light
         let z = pos - arr;
-        let d2: f64 = z.length2() as f64;  // Distance from center of sphere squared
+        let d2: f64 = z.length2() as f64; // Distance from center of sphere squared
         let d = d2.sqrt(); // Distance from center of sphere
         let (z, x, y) = coordinate_system_from_vector(z);
         let (x, y, z) = (x.normalized(), y.normalized(), z.normalized());
@@ -125,7 +126,7 @@ impl LightSource for SphereLight {
         let pos = Point::new(0.0, 0.0, 0.0);
         let radius: f64 = lerp_slice(&self.radii, time) as f64;
 
-        let d2: f64 = (pos - arr).length2() as f64;  // Distance from center of sphere squared
+        let d2: f64 = (pos - arr).length2() as f64; // Distance from center of sphere squared
         let d: f64 = d2.sqrt(); // Distance from center of sphere
 
         if d > radius {

src/main.rs

@@ -41,6 +41,7 @@ mod timer;
 mod tracer;
 mod transform_stack;
 mod triangle;
+mod world;
 
 use std::fs::File;
 use std::io;

src/math/mod.rs

@@ -48,8 +48,8 @@ pub fn fast_pow2(p: f32) -> f32 {
     let z: f32 = clipp - w as f32 + offset;
 
     let i: u32 = ((1 << 23) as f32 *
-                  (clipp + 121.2740575 + 27.7280233 / (4.84252568 - z) -
+                  (clipp + 121.2740575 + 27.7280233 / (4.84252568 - z) - 1.49012907 * z)) as
-                   1.49012907 * z)) as u32;
+                 u32;
 
     unsafe { transmute_copy::<u32, f32>(&i) }
 }

src/objects_split.rs

@@ -64,8 +64,8 @@ pub fn free_sah_split<'a, T, F>(seed: u32, objects: &mut [T], bounder: &F) -> (u
 
     // Build SAH bins
     let sah_bins = {
-        let mut sah_bins =
+        let mut sah_bins = [[(BBox::new(), BBox::new(), 0, 0); SAH_BIN_COUNT - 1];
-            [[(BBox::new(), BBox::new(), 0, 0); SAH_BIN_COUNT - 1]; SPLIT_PLANE_COUNT];
+                            SPLIT_PLANE_COUNT];
         for obj in objects.iter() {
             let tb = lerp_slice(bounder(obj), 0.5);
             let centroid = tb.center().into_vector();

src/parse/data_tree.rs

@@ -287,10 +287,10 @@ fn parse_node<'a>(source_text: (usize, &'a str)) -> ParseResult<'a> {
                     }
                     if let (Token::CloseInner, text4) = next_token(text_remaining) {
                         return Ok(Some((DataTree::Internal {
-                            type_name: type_name,
+                                            type_name: type_name,
-                            ident: Some(n),
+                                            ident: Some(n),
-                            children: children,
+                                            children: children,
-                        },
+                                        },
                                         text4)));
                     } else {
                         return Err(ParseError::MissingCloseInternal(text_remaining.0));
@@ -311,10 +311,10 @@ fn parse_node<'a>(source_text: (usize, &'a str)) -> ParseResult<'a> {
 
                 if let (Token::CloseInner, text3) = next_token(text_remaining) {
                     return Ok(Some((DataTree::Internal {
-                        type_name: type_name,
+                                        type_name: type_name,
-                        ident: None,
+                                        ident: None,
-                        children: children,
+                                        children: children,
-                    },
+                                    },
                                     text3)));
                 } else {
                     return Err(ParseError::MissingCloseInternal(text_remaining.0));
@@ -326,9 +326,9 @@ fn parse_node<'a>(source_text: (usize, &'a str)) -> ParseResult<'a> {
                 let (contents, text3) = parse_leaf_content(text2);
                 if let (Token::CloseLeaf, text4) = next_token(text3) {
                     return Ok(Some((DataTree::Leaf {
-                        type_name: type_name,
+                                        type_name: type_name,
-                        contents: contents,
+                                        contents: contents,
-                    },
+                                    },
                                     text4)));
                 } else {
                     return Err(ParseError::MissingCloseLeaf(text3.0));

src/parse/psy.rs

@@ -9,11 +9,14 @@ use camera::Camera;
 use color::{XYZ, rec709e_to_xyz};
 use math::Matrix4x4;
 use renderer::Renderer;
+use world::World;
 use scene::Scene;
+use light::WorldLightSource;
 
 use super::basics::{ws_u32, ws_f32};
 use super::DataTree;
 use super::psy_assembly::parse_assembly;
+use super::psy_light::parse_distant_disk_light;
 
 
 #[derive(Copy, Clone, Debug)]
@@ -24,7 +27,6 @@ pub enum PsyParseError {
 
 
 /// Takes in a DataTree representing a Scene node and returns
-/// a renderer.
 pub fn parse_scene(tree: &DataTree) -> Result<Renderer, PsyParseError> {
     // Verify we have the right number of each section
     if tree.iter_children_with_type("Output").count() != 1 {
@@ -79,8 +81,8 @@ pub fn parse_scene(tree: &DataTree) -> Result<Renderer, PsyParseError> {
     };
     let scene = Scene {
         name: scene_name,
-        background_color: world,
         camera: camera,
+        world: world,
         root: assembly,
     };
 
@@ -266,9 +268,10 @@ fn parse_camera(tree: &DataTree) -> Result<Camera, PsyParseError> {
 
 
 
-fn parse_world(tree: &DataTree) -> Result<XYZ, PsyParseError> {
+fn parse_world(tree: &DataTree) -> Result<World, PsyParseError> {
     if tree.is_internal() {
         let background_color;
+        let mut lights: Vec<Box<WorldLightSource>> = Vec::new();
 
         // Parse background shader
         let bgs = {
@@ -281,9 +284,10 @@ fn parse_world(tree: &DataTree) -> Result<XYZ, PsyParseError> {
             if bgs.iter_children_with_type("Type").count() != 1 {
                 return Err(PsyParseError::UnknownError);
             }
-            if let &DataTree::Leaf { contents, .. } = bgs.iter_children_with_type("Type")
+            if let &DataTree::Leaf { contents, .. } =
-                .nth(0)
+                bgs.iter_children_with_type("Type")
-                .unwrap() {
+                    .nth(0)
+                    .unwrap() {
                 contents.trim()
             } else {
                 return Err(PsyParseError::UnknownError);
@@ -291,12 +295,12 @@ fn parse_world(tree: &DataTree) -> Result<XYZ, PsyParseError> {
         };
         match bgs_type {
             "Color" => {
-                if let Some(&DataTree::Leaf { contents, .. }) = bgs.iter_children_with_type("Color")
+                if let Some(&DataTree::Leaf { contents, .. }) =
-                    .nth(0) {
+                    bgs.iter_children_with_type("Color")
-                    if let IResult::Done(_, color) = closure!(tuple!(ws_f32,
+                        .nth(0) {
-                                                                     ws_f32,
+                    if let IResult::Done(_, color) =
-                                                                     ws_f32))(contents.trim()
+                        closure!(tuple!(ws_f32, ws_f32, ws_f32))(contents.trim()
-                        .as_bytes()) {
+                            .as_bytes()) {
                         // TODO: proper color space management, not just assuming
                         // rec.709.
                         background_color = XYZ::from_tuple(rec709e_to_xyz(color));
@@ -311,7 +315,22 @@ fn parse_world(tree: &DataTree) -> Result<XYZ, PsyParseError> {
             _ => return Err(PsyParseError::UnknownError),
         }
 
-        return Ok(background_color);
+        // Parse light sources
+        for child in tree.iter_children() {
+            match child {
+                &DataTree::Internal { type_name, .. } if type_name == "DistantDiskLight" => {
+                    lights.push(Box::new(parse_distant_disk_light(&child)?));
+                }
+
+                _ => {}
+            }
+        }
+
+        // Build and return the world
+        return Ok(World {
+            background_color: background_color,
+            lights: lights,
+        });
     } else {
         return Err(PsyParseError::UnknownError);
     }
@@ -321,23 +340,24 @@ fn parse_world(tree: &DataTree) -> Result<XYZ, PsyParseError> {
 
 
 pub fn parse_matrix(contents: &str) -> Result<Matrix4x4, PsyParseError> {
-    if let IResult::Done(_, ns) = closure!(terminated!(tuple!(ws_f32,
+    if let IResult::Done(_, ns) =
-                                                              ws_f32,
+        closure!(terminated!(tuple!(ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32,
+                                    ws_f32,
-                                                              ws_f32),
+                                    ws_f32,
-                                                       nom::eof))(contents.as_bytes()) {
+                                    ws_f32),
+                             nom::eof))(contents.as_bytes()) {
         return Ok(Matrix4x4::new_from_values(ns.0,
                                              ns.4,
                                              ns.8,

src/parse/psy_light.rs

@@ -4,14 +4,70 @@ use std::result::Result;
 
 use nom::IResult;
 
+use math::Vector;
 use color::{XYZ, rec709e_to_xyz};
-use light::{SphereLight, RectangleLight};
+use light::{DistantDiskLight, SphereLight, RectangleLight};
 
 use super::basics::ws_f32;
 use super::DataTree;
 use super::psy::PsyParseError;
 
 
+pub fn parse_distant_disk_light(tree: &DataTree) -> Result<DistantDiskLight, PsyParseError> {
+    if let &DataTree::Internal { ref children, .. } = tree {
+        let mut radii = Vec::new();
+        let mut directions = Vec::new();
+        let mut colors = Vec::new();
+
+        // Parse
+        for child in children.iter() {
+            match child {
+                // Radius
+                &DataTree::Leaf { type_name, contents } if type_name == "Radius" => {
+                    if let IResult::Done(_, radius) = ws_f32(contents.as_bytes()) {
+                        radii.push(radius);
+                    } else {
+                        // Found radius, but its contents is not in the right format
+                        return Err(PsyParseError::UnknownError);
+                    }
+                }
+
+                // Direction
+                &DataTree::Leaf { type_name, contents } if type_name == "Direction" => {
+                    if let IResult::Done(_, direction) =
+                        closure!(tuple!(ws_f32, ws_f32, ws_f32))(contents.as_bytes()) {
+                        directions.push(Vector::new(direction.0, direction.1, direction.2));
+                    } else {
+                        // Found color, but its contents is not in the right format
+                        return Err(PsyParseError::UnknownError);
+                    }
+                }
+
+                // Color
+                &DataTree::Leaf { type_name, contents } if type_name == "Color" => {
+                    if let IResult::Done(_, color) =
+                        closure!(tuple!(ws_f32, ws_f32, ws_f32))(contents.as_bytes()) {
+                        // TODO: handle color space conversions properly.
+                        // Probably will need a special color type with its
+                        // own parser...?
+                        colors.push(XYZ::from_tuple(rec709e_to_xyz(color)));
+                    } else {
+                        // Found color, but its contents is not in the right format
+                        return Err(PsyParseError::UnknownError);
+                    }
+                }
+
+                _ => {}
+            }
+        }
+
+        return Ok(DistantDiskLight::new(radii, directions, colors));
+    } else {
+        return Err(PsyParseError::UnknownError);
+    }
+}
+
+
 pub fn parse_sphere_light(tree: &DataTree) -> Result<SphereLight, PsyParseError> {
     if let &DataTree::Internal { ref children, .. } = tree {
         let mut radii = Vec::new();
@@ -32,9 +88,8 @@ pub fn parse_sphere_light(tree: &DataTree) -> Result<SphereLight, PsyParseError>
 
                 // Color
                 &DataTree::Leaf { type_name, contents } if type_name == "Color" => {
-                    if let IResult::Done(_, color) = closure!(tuple!(ws_f32,
+                    if let IResult::Done(_, color) =
-                                                                     ws_f32,
+                        closure!(tuple!(ws_f32, ws_f32, ws_f32))(contents.as_bytes()) {
-                                                                     ws_f32))(contents.as_bytes()) {
                         // TODO: handle color space conversions properly.
                         // Probably will need a special color type with its
                         // own parser...?
@@ -66,7 +121,7 @@ pub fn parse_rectangle_light(tree: &DataTree) -> Result<RectangleLight, PsyParse
                 // Dimensions
                 &DataTree::Leaf { type_name, contents } if type_name == "Dimensions" => {
                     if let IResult::Done(_, radius) =
-                           closure!(tuple!(ws_f32, ws_f32))(contents.as_bytes()) {
+                        closure!(tuple!(ws_f32, ws_f32))(contents.as_bytes()) {
                         dimensions.push(radius);
                     } else {
                         // Found dimensions, but its contents is not in the right format
@@ -76,9 +131,8 @@ pub fn parse_rectangle_light(tree: &DataTree) -> Result<RectangleLight, PsyParse
 
                 // Color
                 &DataTree::Leaf { type_name, contents } if type_name == "Color" => {
-                    if let IResult::Done(_, color) = closure!(tuple!(ws_f32,
+                    if let IResult::Done(_, color) =
-                                                                     ws_f32,
+                        closure!(tuple!(ws_f32, ws_f32, ws_f32))(contents.as_bytes()) {
-                                                                     ws_f32))(contents.as_bytes()) {
                         // TODO: handle color space conversions properly.
                         // Probably will need a special color type with its
                         // own parser...?

src/parse/psy_mesh_surface.rs

@@ -35,9 +35,8 @@ pub fn parse_mesh_surface(tree: &DataTree) -> Result<TriangleMesh, PsyParseError
 
         // Collect verts for this time sample
         let mut vert_count = 0;
-        while let IResult::Done(remaining, vert) = closure!(tuple!(ws_f32,
+        while let IResult::Done(remaining, vert) =
-                                                                   ws_f32,
+            closure!(tuple!(ws_f32, ws_f32, ws_f32))(raw_text) {
-                                                                   ws_f32))(raw_text) {
             raw_text = remaining;
 
             verts.push(Point::new(vert.0, vert.1, vert.2));

src/renderer.rs

@@ -113,9 +113,10 @@ impl Renderer {
                                                        (halton::sample(0, offset + si as u32),
                                                         halton::sample(1, offset + si as u32)),
                                                        halton::sample(2, offset + si as u32),
-                                                       map_0_1_to_wavelength(
+                                                       map_0_1_to_wavelength(halton::sample(3,
-                                                           halton::sample(3, offset + si as u32)
+                                                                                            offset +
-                                                       ),
+                                                                                            si as
+                                                                                            u32)),
                                                        offset + si as u32);
                                     paths.push(path);
                                     rays.push(ray);
@@ -249,17 +250,17 @@ impl LightPath {
            lds_offset: u32)
            -> (LightPath, Ray) {
         (LightPath {
-            pixel_co: pixel_co,
+             pixel_co: pixel_co,
-            lds_offset: lds_offset,
+             lds_offset: lds_offset,
-            dim_offset: 6,
+             dim_offset: 6,
-            round: 0,
+             round: 0,
-            time: time,
+             time: time,
-            wavelength: wavelength,
+             wavelength: wavelength,
-            interaction: surface::SurfaceIntersection::Miss,
+             interaction: surface::SurfaceIntersection::Miss,
-            light_attenuation: SpectralSample::from_value(1.0, wavelength),
+             light_attenuation: SpectralSample::from_value(1.0, wavelength),
-            pending_color_addition: SpectralSample::new(wavelength),
+             pending_color_addition: SpectralSample::new(wavelength),
-            color: SpectralSample::new(wavelength),
+             color: SpectralSample::new(wavelength),
-        },
+         },
 
          scene.camera.generate_ray(image_plane_co.0,
                                    image_plane_co.1,
@@ -297,13 +298,14 @@ impl LightPath {
                 let light_n = self.next_lds_samp();
                 let light_uvw = (self.next_lds_samp(), self.next_lds_samp(), self.next_lds_samp());
                 xform_stack.clear();
-                if let Some((light_color, shadow_vec, light_pdf, light_sel_pdf)) = scene.root
+                if let Some((light_color, shadow_vec, light_pdf, light_sel_pdf)) =
-                    .sample_lights(xform_stack,
+                    scene.root
-                                   light_n,
+                        .sample_lights(xform_stack,
-                                   light_uvw,
+                                       light_n,
-                                   self.wavelength,
+                                       light_uvw,
-                                   self.time,
+                                       self.wavelength,
-                                   isect) {
+                                       self.time,
+                                       isect) {
                     // Calculate and store the light that will be contributed
                     // to the film plane if the light is not in shadow.
                     self.pending_color_addition = {
@@ -327,7 +329,7 @@ impl LightPath {
                 }
             } else {
                 // Didn't hit anything, so background color
-                self.color += scene.background_color.to_spectral_sample(self.wavelength) *
+                self.color += scene.world.background_color.to_spectral_sample(self.wavelength) *
                               self.light_attenuation;
                 return false;
             }

src/scene.rs

@@ -1,12 +1,13 @@
 use assembly::Assembly;
 use camera::Camera;
-use color::XYZ;
+use world::World;
+
 
 
 #[derive(Debug)]
 pub struct Scene {
     pub name: Option<String>,
-    pub background_color: XYZ,
     pub camera: Camera,
+    pub world: World,
     pub root: Assembly,
 }

src/world.rs

@@ -0,0 +1,8 @@
+use color::XYZ;
+use light::WorldLightSource;
+
+#[derive(Debug)]
+pub struct World {
+    pub background_color: XYZ,
+    pub lights: Vec<Box<WorldLightSource>>,
+}