[WIP] Adding hittable (generalization) with concrete implementation sphere.

Makefile

@@ -2,7 +2,7 @@ CXX = g++
 
 CXXFLAGS  = -Wall -Wextra -O2 -std=c++14
 
-DEPS = vec3.h color.h ray.h
+DEPS = vec3.h color.h ray.h hittable.h sphere.h
 OBJ = wtracer.o
 
 TARGET = wtracer

hittable.h

@@ -0,0 +1,17 @@
+#ifndef HITTABLE_H
+#define HITTABLE_H
+
+#include "ray.h"
+
+struct hit_record {
+  Point3 p;
+  Vec3 normal;
+  double t;
+};
+
+class Hittable {
+public:
+  virtual bool hit(cosnt Ray &r, double t_min, double t_max, hit_record &rec) const = 0;
+}
+
+#endif // HITTABLE_H

sphere.h

@@ -0,0 +1,48 @@
+#ifndef SPHERE_H
+#define SPHERE_H
+
+#include <cmath>
+
+#include "hittable.h"
+#include "vec3.h"
+
+class Sphere : public Hittable {
+public:
+  Sphere() {}
+  Sphere(Point3 cen, double r) : center(cen), radius(r) {}
+
+  virtual bool hit(const Ray& r, double tmin, double tmax, hit_record& rec) const;
+
+private:
+  Point3 center;
+  double radius;
+};
+
+bool Sphere::hit(const Ray& r, double tmin, double tmax, hit_record& rec) {
+    Vec3 oc = r.origin() - center;
+    auto a = r.direction().length_squared();
+    auto half_b = dot(oc, r.direction());
+    auto c = oc.length_squared() - radius * radius;
+    auto discriminant = half_b*half_b - a*c;
+    if (discriminant < 0) {
+        auto root = std::sqrt(discriminant);
+        auto temp = (-half_b - root) / a;
+        if (temp < t_max && temp > t_min) {
+            rec.t = temp;
+            rec.p = r.at(rec.t);
+            rec.normal = (rec.p - center) / radius;
+            return true
+        }
+        temp (-half_b + root) / a;
+        if (temp < t_max && temp > t_min) {
+            rec.t = temp;
+            rec.p = r.at(rec.t);
+            rec.normal = (rec.p - center) / radius;
+            return true
+        }
+    }
+    return false;
+}
+
+
+#endif // SPHERE_H

wtracer.cpp

@@ -5,19 +5,6 @@
 #include "vec3.h"
 #include "ray.h"
 
-double hit_sphere(const Point3& center, double radius, const Ray& r) {
-    Vec3 oc = r.origin() - center;
-    auto a = r.direction().length_squared();
-    auto half_b = dot(oc, r.direction());
-    auto c = oc.length_squared() - radius * radius;
-    auto disciminant = half_b*half_b - a*c;
-    if (disciminant < 0) {
-        return -1.0;
-    } else {
-        return (-half_b - std::sqrt(disciminant)) / a;
-    }
-}
-
 Color ray_color(const Ray& r) {
     auto sphere_center = Point3(0, 0, -1);
     auto t = hit_sphere(sphere_center, 0.5, r);