Sending rays into an empty scene! Hooray!

src/program.cpp

@@ -1,14 +1,33 @@
 #include "color.h"
+#include "ray.h"
 #include "vector3.h"
 
 #include <iostream>
 
+color ray_color(const ray& r){
+    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);
+}
+
 
 int main ()
 {
     // Image 
-    const int image_width = 256;
-    const int image_height = 256;
+    const auto aspect_ratio = 16.0 /9.0;
+    const int image_width = 400;
+    const int image_height = static_cast<int>(image_width /aspect_ratio);
+
+
+    // Camera
+    auto viewport_height = 2.0;
+    auto viewport_width = aspect_ratio * viewport_height;
+    auto focal_length = 1.0;
+
+    auto origin = point3(0,0,0);
+    auto horizontal = vec3(viewport_width, 0, 0);
+    auto vertical = vec3(0, viewport_height, 0);
+    auto lower_left_corner = origin - horizontal/2 - vertical/2 - vec3(0,0,focal_length);
 
     // Render
     std::cout<< "P3\n" << image_width << ' ' << image_height << "\n255\n";
@@ -17,7 +36,10 @@ int main ()
         std::cerr << "\rScanlines remaining: " << j << ' ' << std::flush;
         for(int i = 0; i < image_width; ++i)
         {
-           color pixel_color(double(i)/(image_width-1), double(j)/(image_height-1), 0.25);
+            auto u = double(i) / (image_width-1);
+            auto v = double(j) / (image_height-1);
+            ray r(origin, lower_left_corner+u*horizontal + v* vertical -origin);
+           color pixel_color = ray_color(r);
            write_color(std::cout , pixel_color);
         }
     }

src/ray.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "vector3.h"
+
+class ray{
+    public:
+    ray(){}
+    ray(const point3& origin ,const vec3& direction): orig(origin), dir(direction){}
+
+    point3 origin() const {return orig;}
+    vec3 direction() const {return dir;}
+
+    point3 at(double t) const {
+        return orig + t*dir;
+    }
+
+    public:
+        point3 orig;
+        vec3 dir;
+
+};