From 6267dce475c85424f297b5bca98f2781d324df79 Mon Sep 17 00:00:00 2001
From: Michael Zhang <mail@mzhang.io>
Date: Thu, 2 Feb 2023 19:06:04 -0600
Subject: [PATCH] Filter out t < 0

---
 assignment-1a/src/main.rs               |  2 +-
 assignment-1a/src/scene/cylinder.rs     | 16 +++++++++-------
 assignment-1a/src/scene/sphere.rs       | 11 +++++++++--
 assignment-1a/src/{math.rs => utils.rs} | 11 +++++++++++
 4 files changed, 30 insertions(+), 10 deletions(-)
 rename assignment-1a/src/{math.rs => utils.rs} (72%)

diff --git a/assignment-1a/src/main.rs b/assignment-1a/src/main.rs
index 588a297..08fcbe1 100644
--- a/assignment-1a/src/main.rs
+++ b/assignment-1a/src/main.rs
@@ -3,7 +3,7 @@ extern crate anyhow;
 
 mod image;
 mod input_file;
-mod math;
+mod utils;
 mod ray;
 mod scene;
 
diff --git a/assignment-1a/src/scene/cylinder.rs b/assignment-1a/src/scene/cylinder.rs
index 87b552a..90faac4 100644
--- a/assignment-1a/src/scene/cylinder.rs
+++ b/assignment-1a/src/scene/cylinder.rs
@@ -1,7 +1,7 @@
 use nalgebra::Vector3;
-use ordered_float::NotNan;
 
-use crate::{math::compute_rotation_matrix, ray::Ray};
+use crate::ray::Ray;
+use crate::utils::{compute_rotation_matrix, min_f64};
 
 use super::data::ObjectKind;
 
@@ -113,12 +113,14 @@ impl ObjectKind for Cylinder {
       ray_point.x.powi(2) + ray_point.y.powi(2) <= self.radius.powi(2)
     });
 
-    let solutions = side_solutions.into_iter().chain(end_solutions.into_iter());
+    let solutions = side_solutions
+      .into_iter()
+      .chain(end_solutions.into_iter())
+      // Remove any t < 0, since that means it's behind the viewer and we
+      // can't see it.
+      .filter(|t| *t >= 0.0);
 
     // Return the minimum solution
-    solutions
-      .filter_map(|t| NotNan::new(t).ok())
-      .min()
-      .map(|t| t.into_inner())
+    min_f64(solutions)
   }
 }
diff --git a/assignment-1a/src/scene/sphere.rs b/assignment-1a/src/scene/sphere.rs
index 0acd760..4e51043 100644
--- a/assignment-1a/src/scene/sphere.rs
+++ b/assignment-1a/src/scene/sphere.rs
@@ -1,6 +1,6 @@
 use nalgebra::Vector3;
 
-use crate::ray::Ray;
+use crate::{ray::Ray, utils::min_f64};
 
 use super::data::ObjectKind;
 
@@ -40,7 +40,14 @@ impl ObjectKind for Sphere {
         let solution_1 = (-b + discriminant.sqrt()) / (2.0 * a);
         let solution_2 = (-b - discriminant.sqrt()) / (2.0 * a);
 
-        Some(solution_1.min(solution_2))
+        let solutions = [solution_1, solution_2]
+          .into_iter()
+          // Remove any t < 0, since that means it's behind the viewer and we
+          // can't see it.
+          .filter(|t| *t >= 0.0);
+
+        // Return the minimum solution
+        min_f64(solutions)
       }
 
       // Probably hit some NaN or Infinity value due to faulty inputs...
diff --git a/assignment-1a/src/math.rs b/assignment-1a/src/utils.rs
similarity index 72%
rename from assignment-1a/src/math.rs
rename to assignment-1a/src/utils.rs
index e04f80b..73fe3db 100644
--- a/assignment-1a/src/math.rs
+++ b/assignment-1a/src/utils.rs
@@ -1,4 +1,15 @@
 use nalgebra::{Matrix3, Vector3};
+use ordered_float::NotNan;
+
+/// Finds the minimum of an iterator of f64s, ignoring any NaN values
+pub fn min_f64<I>(i: I) -> Option<f64>
+where
+  I: Iterator<Item = f64>,
+{
+  i.filter_map(|i| NotNan::new(i).ok())
+    .min()
+    .map(|i| i.into_inner())
+}
 
 /// Calculate the rotation matrix between the 2 given vectors
 /// Based on the method here: https://math.stackexchange.com/a/897677