diff --git a/src/camera.h b/src/camera.h
index 462a3df..79c1fad 100644
--- a/src/camera.h
+++ b/src/camera.h
@@ -1,7 +1,11 @@
 #pragma once
 
+#include <iostream>
+
+#include "image.h"
 #include "ray.h"
 #include "raytracer.h"
+#include "renderobject.h"
 #include "vec3.h"
 
 class Camera {
@@ -27,6 +31,19 @@ class Camera {
 
     constexpr Vec3 centre() const { return centre_; }
 
+    constexpr void Render(Image& img, const RenderObject& world) const {
+        for (u32 j = 0; j < img.height(); j++) {
+            std::clog << "\rWriting line " << j << " of " << img.height() << std::flush;
+
+            for (u32 i = 0; i < img.width(); i++) {
+                auto ray = CastRay(i, j);
+
+                img[i, j] = Cast(ray, world);
+            }
+        }
+    }
+
+   private:
     constexpr Vec3 Image2World(u32 i, u32 j) const {
         return pixel_00_ + i * d_u_pixel_ + j * d_v_pixel_;
     }
@@ -39,7 +56,6 @@ class Camera {
         return Ray{centre(), ray_direction};
     }
 
-   private:
     Vec3 centre_;
 
     // position of pixel 0, 0
diff --git a/src/main.cc b/src/main.cc
index 1d1c406..26e5699 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -2,40 +2,13 @@
 #include <memory>
 
 #include "camera.h"
-#include "colour.h"
 #include "image.h"
-#include "interval.h"
-#include "ray.h"
 #include "raytracer.h"
 #include "renderobject.h"
 #include "renderobjectlist.h"
 #include "sphere.h"
 #include "vec3.h"
 
-Colour RayColour(const Ray& ray, const RenderObject& world) {
-    auto hit_record = world.hit(ray, Interval::kPositive);
-    // auto hit_record = world.hit(ray, Interval{0.505, kInf});
-
-    if (hit_record.has_value()) {
-        // assert(hit_record.front_face);
-
-        Vec3 n = hit_record->normal;
-
-        if (!hit_record->front_face) {
-            // return Colour{0.0, 0.0, 0.0};
-            return Colour::kBlack;
-        }
-
-        return Colour{0.5 * (n + Vec3{1, 1, 1})};
-    }
-
-    auto unit_dir = ray.direction().normed();
-
-    double a = 0.5 * (unit_dir.y() + 1.0);
-
-    return (1.0 - a) * Colour{1.0, 1.0, 1.0} + a * Colour{0.5, 0.7, 1.0};
-}
-
 int main(int /* argc */, char* /* argv */[]) {
     // image
 
@@ -66,15 +39,7 @@ int main(int /* argc */, char* /* argv */[]) {
 
     // render
 
-    for (u32 j = 0; j < img.height(); j++) {
-        std::clog << "\rWriting line " << j << " of " << img.height() << std::flush;
-
-        for (u32 i = 0; i < img.width(); i++) {
-            auto ray = camera.CastRay(i, j);
-
-            img[i, j] = RayColour(ray, world);
-        }
-    }
+    camera.Render(img, world);
 
     std::cout << img;
 
diff --git a/src/renderobject.h b/src/renderobject.h
index f57cfb3..bbbec7b 100644
--- a/src/renderobject.h
+++ b/src/renderobject.h
@@ -3,6 +3,7 @@
 #include <memory>
 #include <optional>
 
+#include "colour.h"
 #include "interval.h"
 #include "ray.h"
 #include "vec3.h"
@@ -30,3 +31,27 @@ class RenderObject {
 };
 
 using SharedRenderObject = std::shared_ptr<RenderObject>;
+
+constexpr Colour Cast(const Ray& ray, const RenderObject& world) {
+    auto hit_record = world.hit(ray, Interval::kPositive);
+    // auto hit_record = world.hit(ray, Interval{0.505, kInf});
+
+    if (hit_record.has_value()) {
+        // assert(hit_record.front_face);
+
+        Vec3 n = hit_record->normal;
+
+        if (!hit_record->front_face) {
+            // return Colour{0.0, 0.0, 0.0};
+            return Colour::kBlack;
+        }
+
+        return Colour{0.5 * (n + Vec3{1, 1, 1})};
+    }
+
+    auto unit_dir = ray.direction().normed();
+
+    double a = 0.5 * (unit_dir.y() + 1.0);
+
+    return (1.0 - a) * Colour{1.0, 1.0, 1.0} + a * Colour{0.5, 0.7, 1.0};
+}