feat: add sphere

main.cc

@@ -1,20 +1,60 @@
 #include "color.h"
+#include "ray.h"
 #include "vec3.h"
 
 #include <iostream>
 
+double hit_sphere(const point3& center, double radius, const ray& r) {
+	vec3 oc = r.origin() - center;
+	auto a = r.direction().length_squared();
+	auto half_b = dot(oc, r.direction());
+	auto c = oc.length_squared() - radius*radius;
+	auto discriminant = half_b*half_b - a*c;
+
+	if (discriminant < 0) {
+		return -1.0;
+	} else {
+		return (-half_b - sqrt(discriminant)) / a;
+	}
+}
+
+color ray_color(const ray& r) {
+	auto t = hit_sphere(point3(0, 0, -1), 0.5, r);
+	if (t > 0.0) {
+		vec3 N = unit_vector(r.at(t) - vec3(0, 0, -1));
+		return 0.5*color(N.x()+1, N.y()+1, N.z()+1);
+	}
+
+	vec3 unit_direction = unit_vector(r.direction());
+	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";
 	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);
 		}
 	}

ray.h

@@ -0,0 +1,25 @@
+#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;
+		}
+
+	public:
+		point3 orig;
+		vec3 dir;
+};
+
+#endif