Adding rays, origin and horizon.

Makefile

@@ -2,7 +2,7 @@ CXX = g++
 
 CXXFLAGS  = -Wall -Wextra -O2 -std=c++14
 
-DEPS = vec3.h color.h
+DEPS = vec3.h color.h ray.h
 OBJ = wtracer.o
 
 TARGET = wtracer

ray.h

@@ -0,0 +1,24 @@
+#ifndef RAY_H
+#define RAY_H
+
+#include "vec3.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;
+    }
+
+   private:
+    Point3 orig;
+    Vec3 dir;
+};
+
+#endif //RAY_H

wtracer.cpp

@@ -2,19 +2,37 @@
 
 #include "color.h"
 #include "vec3.h"
+#include "ray.h"
+
+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() {
-    const int image_width = 256;
-    const int image_height = 256;
+    const auto aspect_ratio = 16.0 / 9.0;
+    const int image_width = 1280;
+    const int image_height = static_cast<int>(image_width / aspect_ratio);
 
     std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";
 
+    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);
+
     for (int j = image_height - 1; j >= 0; --j) {
         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);
         }
     }