diff --git a/wtracer.cpp b/wtracer.cpp
index 6aa422f..5f7e7c5 100644
--- a/wtracer.cpp
+++ b/wtracer.cpp
@@ -4,7 +4,18 @@
 #include "vec3.h"
 #include "ray.h"
 
+bool hit_sphere(const Point3& center, double radius, const Ray& r) {
+    Vec3 oc = r.origin() - center;
+    auto a = dot(r.direction(), r.direction());
+    auto b = 2.0 * dot(oc, r.direction());
+    auto c = dot(oc, oc) - radius * radius;
+    auto disciminant = b*b - 4*a*c;
+    return disciminant > 0;
+}
+
 Color ray_color(const Ray& r) {
+    if (hit_sphere(Point3(0, 0, -1), 0.5, r))
+        return Color(1, 0, 0);
     Vec3 unit_direction = unit_vector(r.direction());
     auto t = 0.5 * (unit_direction.y() + 1.0);
     return (1.0 - t) * Color(1.0, 1.0, 1.0) + t * Color(0.5, 0.7, 1.0);