calculate nearest hit

src/Geometry.cc

@@ -1,6 +1,7 @@
 #include "Geometry.h"
 
 #include <Eigen/Dense>
+#include <cmath>
 
 Vector3f Geometry::diffuse() const { return cd; }
 Vector3f Geometry::specular() const { return cs; }
@@ -10,13 +11,24 @@ void Geometry::setTransform(const Matrix4f &transform) {
   this->transform = transform;
 }
 
-bool Sphere::intersect(const Ray &r) const {
+Optional<float> Sphere::intersect(const Ray &r) const {
   Vector3f originCenter = r.getOrigin() - center;
   float a = r.getDirection().dot(r.getDirection());
   float b = 2.0f * originCenter.dot(r.getDirection());
   float c = originCenter.dot(originCenter) - radius * radius;
 
-  return b * b - 4 * a * c >= 0;
+  float delta = b * b - 4 * a * c;
+  if (delta >= 0) {
+    float t1 = (-b + sqrt(delta)) / 2.0f / a;
+    float t2 = (-b - sqrt(delta)) / 2.0f / a;
+    float mint = std::min(t1, t2);
+    float maxt = std::max(t1, t2);
+    return maxt <= 0
+               ? Optional<float>::nullopt
+               : (mint < 0 ? Optional<float>(maxt) : Optional<float>(mint));
+  }
+
+  return Optional<float>::nullopt;
 }
 
 bool isInRectangle(const Vector3f &p, const Vector3f &a, const Vector3f &b,
@@ -30,18 +42,19 @@ bool isInRectangle(const Vector3f &p, const Vector3f &a, const Vector3f &b,
          (s1 <= 0 && s2 <= 0 && s3 <= 0 && s4 <= 0);
 }
 
-bool Rectangle::intersect(const Ray &r) const {
+Optional<float> Rectangle::intersect(const Ray &r) const {
   Vector3f normal = (p2 - p1).cross(p3 - p1).normalized();
 
   float denom = normal.dot(r.getDirection());
   if (abs(denom) < 1e-6f)
-    return false;
+    return Optional<float>::nullopt;
 
   float t = -normal.dot(r.getOrigin() - p1) / denom;
   if (t <= 0)
-    return false;
+    return Optional<float>::nullopt;
 
   Vector3f p = r.getOrigin() + t * r.getDirection();
 
-  return isInRectangle(p, p1, p2, p3, p4, normal);
+  return isInRectangle(p, p1, p2, p3, p4, normal) ? Optional<float>(t)
+                                                  : Optional<float>::nullopt;
 }

src/Geometry.h

@@ -1,6 +1,7 @@
 #ifndef GEOMETRY_H_
 #define GEOMETRY_H_
 
+#include "Optional.h"
 #include "Ray.h"
 
 #include <Eigen/Core>
@@ -8,6 +9,7 @@
 using Eigen::Matrix;
 using Eigen::Matrix4f;
 using Eigen::Vector3f;
+using utils::Optional;
 
 // Abstract class for Geometries
 class Geometry {
@@ -15,7 +17,7 @@ public:
   enum class Type { SPHERE, RECTANGLE };
 
   virtual ~Geometry() = default;
-  virtual bool intersect(const Ray &) const = 0;
+  virtual Optional<float> intersect(const Ray &) const = 0;
 
 protected:
   Geometry(Type type, float ka, float kd, float ks, const Vector3f &ca,
@@ -42,7 +44,7 @@ public:
       : Geometry(Type::SPHERE, ka, kd, ks, ca, cd, cs, pc), radius(radius),
         center(center) {}
 
-  bool intersect(const Ray &) const override;
+  Optional<float> intersect(const Ray &) const override;
 
 private:
   float radius;
@@ -57,7 +59,7 @@ public:
       : Geometry(Type::RECTANGLE, ka, kd, ks, ca, cd, cs, pc), p1(p1), p2(p2),
         p3(p3), p4(p4) {}
 
-  bool intersect(const Ray &) const override;
+  Optional<float> intersect(const Ray &) const override;
 
 private:
   Vector3f p1, p2, p3, p4;

src/HitRecord.cc

@@ -0,0 +1,7 @@
+#include "HitRecord.h"
+
+bool HitRecord::operator<(const HitRecord &other) const {
+  return this->t > other.t; // to get the nearest t
+}
+
+Geometry *HitRecord::geometry() const { return g; }

src/HitRecord.h

@@ -0,0 +1,19 @@
+#ifndef HITRECORD_H_
+#define HITRECORD_H_
+
+#include "Geometry.h"
+
+class HitRecord {
+public:
+  HitRecord(float t, Geometry *g) : t(t), g(g) {}
+  bool operator<(const HitRecord &) const;
+
+private:
+  float t;
+  Geometry *g;
+
+public:
+  Geometry *geometry() const;
+};
+
+#endif // !HITRECORD_H_

src/Optional.h

@@ -0,0 +1,25 @@
+#ifndef OPTIONAL_H_
+
+namespace utils {
+
+// I write this class because we are using C++14
+// so std::optional is not available
+template <typename T> class Optional {
+public:
+  Optional() : hasValue_(false) {}
+  Optional(T value) : value_(value), hasValue_(true) {}
+
+  bool hasValue() const { return hasValue_; }
+  T value() const { return value_; }
+
+  static const Optional nullopt;
+
+private:
+  T value_;
+  bool hasValue_;
+};
+
+template <typename T> const Optional<T> Optional<T>::nullopt = Optional<T>();
+} // namespace utils
+
+#endif // !OPTIONAL_H_

src/RayTracer.cc

@@ -1,11 +1,15 @@
 #include "RayTracer.h"
 #include "../external/simpleppm.h"
+#include "HitRecord.h"
 #include "Output.h"
 #include "Parser.h"
 #include "Ray.h"
 
 #include <Eigen/Core>
 #include <cmath>
+#include <queue>
+
+using std::priority_queue;
 
 void RayTracer::parse() {
   for (auto i = json["output"].begin(); i != json["output"].end(); ++i)
@@ -46,15 +50,20 @@ void RayTracer::render(Scene *scene) {
   for (int y = 0; y < height; ++y)
     for (int x = 0; x < width; ++x) {
       Ray ray = getRay(x, y, cameraPos, pxUpperLeft, du, dv);
+      priority_queue<HitRecord> records;
+      for (auto g : geometries) {
+        Optional<float> t = g->intersect(ray);
+        if (t.hasValue())
+          records.push(HitRecord(t.value(), g));
+      }
 
-      for (auto g : geometries)
-        if (g->intersect(ray)) {
-          Vector3f diffuse = g->diffuse();
-          buffer->r(y * width + x, diffuse.x());
-          buffer->g(y * width + x, diffuse.y());
-          buffer->b(y * width + x, diffuse.z());
-          break;
-        }
+      if (!records.empty()) {
+        HitRecord hit = records.top();
+        Vector3f diffuse = hit.geometry()->diffuse();
+        buffer->r(y * width + x, diffuse.x());
+        buffer->g(y * width + x, diffuse.y());
+        buffer->b(y * width + x, diffuse.z());
+      }
     }
 
   outputs.push_back(buffer);