Bias shadow rays to fix noise in image

src/camera.rs

@@ -2,7 +2,7 @@ use nalgebra::{convert, RealField, Vector3};
 
 use super::colour::{ColourRgbF, NamedColour};
 use super::image::ImageRgbF;
-use super::integrators::{DirectionalLight, Integrator, PhongIntegrator};
+use super::integrators::{DirectionalLight, Integrator, WhittedIntegrator};
 use super::raycasting::Ray;
 use super::sampler::Sampler;
 use super::scene::Scene;
@@ -69,13 +69,20 @@ pub fn render_scene<T: RealField>(output_image: &mut ImageRgbF<T>, scene: &Scene
         scene.camera_location,
     );
     let ambient_intensity: T = convert(0.0);
-    let directional_intensity: T = convert(0.9);
-    let integrator = PhongIntegrator::<T> {
+    let directional_intensity1: T = convert(0.7);
+    let directional_intensity2: T = convert(0.3);
+    let integrator = WhittedIntegrator::<T> {
         ambient_light: ColourRgbF::from_named(NamedColour::White) * ambient_intensity,
-        lights: vec![DirectionalLight {
+        lights: vec![
+            DirectionalLight {
                 direction: Vector3::new(convert(1.0), convert(1.0), convert(-1.0)).normalize(),
-            colour: ColourRgbF::from_named(NamedColour::White) * directional_intensity,
-        }],
+                colour: ColourRgbF::from_named(NamedColour::White) * directional_intensity1,
+            },
+            DirectionalLight {
+                direction: Vector3::new(convert(-0.5), convert(2.0), convert(-0.5)).normalize(),
+                colour: ColourRgbF::from_named(NamedColour::White) * directional_intensity2,
+            },
+        ],
     };
     let sampler = Sampler { scene };
     for column in 0..output_image.get_width() {

src/integrators.rs

@@ -1,4 +1,4 @@
-use nalgebra::{RealField, Vector3};
+use nalgebra::{convert, RealField, Vector3};
 
 use super::colour::ColourRgbF;
 use super::raycasting::{IntersectionInfo, Ray};
@@ -13,24 +13,28 @@ pub struct DirectionalLight<T: RealField> {
     pub colour: ColourRgbF<T>,
 }
 
-pub struct PhongIntegrator<T: RealField> {
+pub struct WhittedIntegrator<T: RealField> {
     pub ambient_light: ColourRgbF<T>,
     pub lights: Vec<DirectionalLight<T>>,
 }
 
-impl<T: RealField> Integrator<T> for PhongIntegrator<T> {
+// TODO: Get rid of the magic bias number, which should be calculated base on expected error
+// bounds and tangent direction
+impl<T: RealField> Integrator<T> for WhittedIntegrator<T> {
     fn integrate(&self, sampler: &Sampler<T>, info: &IntersectionInfo<T>) -> ColourRgbF<T> {
         self.lights
             .iter()
-            .map(
-                |light| match sampler.sample(&Ray::new(info.location, light.direction)) {
+            .map(|light| {
+                match sampler
+                    .sample(&Ray::new(info.location, light.direction).bias(convert(0.000000001)))
+                {
                     Some(_) => self.ambient_light,
                     None => {
                         info.material.bsdf()(info.retro, light.direction, light.colour)
                             * light.direction.dot(&info.normal)
                     }
-                },
-            )
+                }
+            })
             .fold(self.ambient_light, |a, b| a + b)
     }
 }

src/raycasting.rs

@@ -21,6 +21,10 @@ impl<T: RealField> Ray<T> {
     pub fn point_at(&self, t: T) -> Vector3<T> {
         return self.origin + self.direction * t;
     }
+
+    pub fn bias(&self, amount: T) -> Ray<T> {
+        Ray::new(self.origin + self.direction * amount, self.direction)
+    }
 }
 
 #[derive(Debug)]