Add light attenuation

assignment-1b/examples/attenuation-demo.txt

@@ -0,0 +1,15 @@
+imsize 600 200
+eye 0 0 15
+viewdir 0 0 -1
+hfov 90
+updir 0 1 0
+bkgcolor 0.4 0.4 0.4
+
+attlight -15 10 5 1 1 1 1 0 0.25 0.03
+
+mtlcolor 0.6 1 0.8 1 1 1 0.4 1 0.5 15
+sphere -10 0 0 2
+sphere -5 0 0 2
+sphere 0 0 0 2
+sphere 5 0 0 2
+sphere 10 0 0 2

assignment-1b/src/scene/data.rs

@@ -66,7 +66,12 @@ pub struct Material {
 #[derive(Debug)]
 pub enum LightKind {
   /// A point light source exists at a point and emits light in all directions
-  Point { location: Vector3<f64> },
+  Point {
+    location: Vector3<f64>,
+
+    /// Whether light attenuation is enabled for this light
+    attenuation: Option<Attenuation>,
+  },
 
   /// A directional light source exists at an infinitely far location but emits
   /// light in a specific direction
@@ -87,7 +92,7 @@ impl Light {
   /// light source
   pub fn direction_from(&self, point: Vector3<f64>) -> Vector3<f64> {
     match self.kind {
-      LightKind::Point { location } => location - point,
+      LightKind::Point { location, .. } => location - point,
       LightKind::Directional { direction } => -direction,
     }
     .normalize()
@@ -131,6 +136,28 @@ impl Default for DepthCueing {
   }
 }
 
+/// Light attenuation dropoff coefficients
+#[derive(Debug)]
+pub struct Attenuation {
+  pub c1: f64,
+  pub c2: f64,
+  pub c3: f64,
+}
+
+/// A default implementation here needs to simulate what would happen if there
+/// was no light attenuation specified. In this case, c1 would just be a
+/// constant of 1 and all the coefficients for anything involving distance would
+/// be zeroed out
+impl Default for Attenuation {
+  fn default() -> Self {
+    Self {
+      c1: 1.0,
+      c2: 0.0,
+      c3: 0.0,
+    }
+  }
+}
+
 impl Scene {
   /// Determine the boundaries of the viewing window in world coordinates
   pub fn compute_viewing_window(&self, distance: f64) -> Rect {

assignment-1b/src/scene/illumination.rs

@@ -61,14 +61,37 @@ impl Scene {
             .max(0.0)
             .powf(material.exponent);
 
+        // Shadow coefficient between 0 and 1 to control how bright this pixel
+        // should be from being in the shadow of another object (could be
+        // between 0 and 1 when applying soft shadows)
         let shadow_coefficient = self.compute_shadow_coefficient(
           obj_idx,
           intersection_context.point,
           light,
         );
 
+        let attenuation_coefficient = match &light.kind {
+          LightKind::Point {
+            location,
+            attenuation: Some(att),
+          } => {
+            let dist = (location - intersection_context.point).norm();
+            let denom = att.c1 + att.c2 * dist + att.c3 * dist.powi(2);
+            if denom == 0.0 {
+              warn!("Light attenuation coefficients produced a denominator of 0. Check your inputs...");
+              1.0 // Some kind of graceful fallback here
+            } else {
+              1.0 / denom
+            }
+          }
+          _ => 1.0,
+        };
+
         let diffuse_and_specular = diffuse_component + specular_component;
-        shadow_coefficient * light.color.component_mul(&diffuse_and_specular)
+
+        attenuation_coefficient
+          * shadow_coefficient
+          * light.color.component_mul(&diffuse_and_specular)
       })
       .sum();
 
@@ -141,7 +164,7 @@ impl Scene {
         match light.kind {
           // In the case of point lights, we must check to see if both t > 0 and
           // t is less than the time it took to even get to the light.
-          LightKind::Point { location } => {
+          LightKind::Point { location, .. } => {
             let light_time = (location - ray.origin).norm();
 
             if intersection_time <= 0.0 || intersection_time >= light_time {

assignment-1b/src/scene/input_file.rs

@@ -5,7 +5,7 @@ use nalgebra::Vector3;
 
 use crate::scene::{
   cylinder::Cylinder,
-  data::{Light, LightKind, Material, Object},
+  data::{Light, LightKind, Material, Object, Attenuation},
   sphere::Sphere,
   Scene,
 };
@@ -79,6 +79,33 @@ impl Scene {
               },
               1 => LightKind::Point {
                 location: read_vec3(0)?,
+                attenuation: None,
+              },
+              _ => bail!("Invalid w; must be either 0 or 1"),
+            };
+            let light = Light {
+              kind,
+              color: read_vec3(4)?,
+            };
+            scene.lights.push(light);
+          }
+
+          // attlight x y z w r g b c1 c2 c3
+          "attlight" => {
+            ensure!(parts.len() == 10, "Attenuated light requires 10 params");
+
+            let kind = match parts[3] as usize {
+              // TODO: Is this even defined? Pending TA answer
+              0 => LightKind::Directional {
+                direction: read_vec3(0)?,
+              },
+              1 => LightKind::Point {
+                location: read_vec3(0)?,
+                attenuation: Some(Attenuation {
+                  c1: parts[7],
+                  c2: parts[8],
+                  c3: parts[9],
+                }),
               },
               _ => bail!("Invalid w; must be either 0 or 1"),
             };

assignment-1b/src/scene/mod.rs

@@ -8,7 +8,7 @@ use nalgebra::Vector3;
 
 use crate::image::Color;
 
-use self::data::{DepthCueing, Light, Material, Object};
+use self::data::{DepthCueing, Light, Material, Object, Attenuation};
 
 #[derive(Debug, Default)]
 pub struct Scene {
@@ -26,6 +26,7 @@ pub struct Scene {
   /// Background color
   pub bkg_color: Color,
   pub depth_cueing: DepthCueing,
+  pub attenuation: Attenuation,
 
   pub materials: Vec<Material>,
   pub lights: Vec<Light>,

assignment-1b/writeup.md

@@ -5,13 +5,15 @@ output: pdf_document
 
 # Raytracer part B
 
-This project implements a raytracer with Blinn-Phong illumination implemented.
-The primary formula that is used by this implementation is:
+This project implements a raytracer with Blinn-Phong illumination and shadows
+implemented. The primary formula that is used by this implementation is:
 
 \begin{equation}
 I_{\lambda} =
 k_a O_{d\lambda} +
 \sum_{i=1}^{n_\textrm{lights}} \left(
+f_\textrm{att} \cdot
+S_i \cdot
 IL_{i\lambda} \left[
 k_d O_{d\lambda} \max ( 0, \vec{N} \cdot \vec{L_i} ) +
 k_s O_{s\lambda} \max ( 0, \vec{N} \cdot \vec{H_i} )^n
@@ -26,6 +28,8 @@ Where:
 - $k_d$ is the material's diffuse reflectivity
 - $k_s$ is the material's specular reflectivity
 - $n_\textrm{lights}$ is the number of lights
+- $f_\textrm{att}$ is the light attenuation factor (1.0 if attenuation is not on)
+- $S_i$ is the shadow coefficient for light $i$
 - $IL_{i\lambda}$ is the intensity of light $i$
 - $O_{d\lambda}$ is the object's diffuse color
 - $O_{s\lambda}$ is the object's specular color
@@ -35,6 +39,11 @@ Where:
   direction to the viewer
 - $n$ is the exponent for the specular component
 
+In this report we will look through how these various factors influence the
+rendering of the scene. All the images along with their source `.txt` files,
+rendered `.ppm` files, and converted `.png` files can be found in the `examples`
+directory of this handin.
+
 ## Varying $k_a$
 
 $k_a$ is the strength of ambient light. It's used as a coefficient for the
@@ -99,6 +108,28 @@ we can get some soft shadow effects like this:
 ![Soft shadows](examples/soft-shadow-demo.png){width=360px}
 \
 
+## Light attenuation
+
+Light attenuation is when more of the light is applied for objects that are
+closer to a particular light source. The function that's applied is an inverse
+quadratic formula with respect to the distance the object is from the light:
+
+\begin{equation}
+f_\textrm{att}(d) = \frac{1}{c_1 + c_2 d + c_3 d^2}
+\end{equation}
+
+Where:
+
+- $f_\textrm{att}$ is the attenuation factor
+- $d$ is the distance the object is from the light
+- $c_1$, $c_2$, and $c_3$ are user-supplied coefficients
+
+As you can see below, the effect of the light drops off with the distance from
+the light (light coming from the left):
+
+![Light attenuation](examples/attenuation-demo.png){width=360px}
+\
+
 ## Depth Cueing
 
 Depth cueing is when the objects further from the viewer have a lower opacity to
@@ -117,4 +148,3 @@ The model cannot be used to represent TODO
 
 ![Objects in the scene](examples/objects.png){width=360px}
 \
-