Add 3 new type of object: Sphere, Object and Intersect.

Add Intersect object as a way to report where a ray intersect another object and which one it is.
Add an Object base class for all object that can be rendered.
Add the Sphere object.

tests/sphere_test.cpp

@@ -0,0 +1,65 @@
+/*
+ *  DoRayMe - a quick and dirty Raytracer
+ *  Sphere unit tests
+ *
+ *  Created by Manoël Trapier
+ *  Copyright (c) 2020 986-Studio.
+ *
+ */
+#include <ray.h>
+#include <sphere.h>
+#include <gtest/gtest.h>
+
+
+TEST(SphereTest, A_ray_intersect_a_sphere_at_two_points)
+{
+    Ray r = Ray(Point(0, 0, -5), Vector(0, 0, 1));
+    Sphere s = Sphere();
+    Intersect xs = s.intersect(r);
+
+    ASSERT_EQ(xs.count(), 2);
+    ASSERT_EQ(xs[0]->t, 4.0);
+    ASSERT_EQ(xs[1]->t, 6.0);
+}
+
+TEST(SphereTest, A_ray_intersect_a_sphere_at_a_tangent)
+{
+    Ray r = Ray(Point(0, 1, -5), Vector(0, 0, 1));
+    Sphere s = Sphere();
+    Intersect xs = s.intersect(r);
+
+    ASSERT_EQ(xs.count(), 2);
+    ASSERT_EQ(xs[0]->t, 5.0);
+    ASSERT_EQ(xs[1]->t, 5.0);
+}
+
+TEST(SphereTest, A_ray_miss_a_sphere)
+{
+    Ray r = Ray(Point(0, 2, -5), Vector(0, 0, 1));
+    Sphere s = Sphere();
+    Intersect xs = s.intersect(r);
+
+    ASSERT_EQ(xs.count(), 0);
+}
+
+TEST(SphereTest, A_ray_originate_inside_a_sphere)
+{
+    Ray r = Ray(Point(0, 0, 0), Vector(0, 0, 1));
+    Sphere s = Sphere();
+    Intersect xs = s.intersect(r);
+
+    ASSERT_EQ(xs.count(), 2);
+    ASSERT_EQ(xs[0]->t, -1.0);
+    ASSERT_EQ(xs[1]->t, 1.0);
+}
+
+TEST(SphereTest, A_sphere_is_behind_a_ray)
+{
+    Ray r = Ray(Point(0, 0, 5), Vector(0, 0, 1));
+    Sphere s = Sphere();
+    Intersect xs = s.intersect(r);
+
+    ASSERT_EQ(xs.count(), 2);
+    ASSERT_EQ(xs[0]->t, -6.0);
+    ASSERT_EQ(xs[1]->t, -4.0);
+}