Add hittable interface and hit infos on hit

1 files changed, 37 insertions, 0 deletions

diff --git a/src/sphere.cpp b/src/sphere.cpp
new file mode 100644
index 0000000..31915a2
--- /dev/null
+++ b/src/sphere.cpp
@@ -0,0 +1,37 @@
+#include "sphere.hpp"
+
+sphere::sphere(point3 center, double radius) : center(center), radius(radius)
+{}
+
+bool sphere::hit(const ray& r, double t_min, double t_max, struct hit_info& info) const {
+    // Vector from the ray origin to sphere position
+    vec3 origin_center = r.origin - center;
+
+    double a = r.direction.dot(r.direction);
+    double half_b = r.direction.dot(origin_center);
+    double c = origin_center.dot(origin_center) - radius * radius;
+    double discriminant = half_b * half_b - a * c;
+
+    if (discriminant < 0) {
+        return false;
+    }
+
+    double sq_discriminant = sqrt(discriminant);
+    double t = (-half_b - sq_discriminant) / a ;
+
+    if (t_min > t || t_max < t) {
+        t = (-half_b + sq_discriminant) / a ;
+
+        if (t_min > t || t_max < t) {
+            return false;
+        }
+    }
+
+    info.t = t;
+    info.point = r.at(t);
+
+    vec3 out_normal = (info.point - center).unit();
+    info.set_face_normal(r, out_normal);
+
+    return true;
+}