Generate and color a sphere based on surface normal

Author: neerajsamtani

.gitignore

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+learning_log.txt

.gitignore~

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-# Ray Tracer
-
-Building a fully functional ray tracer from scratch based on the "Ray Tracing" series by Peter Shirley.
-
-### In Progress
-
-- Simple brute-force path tracer. 
-
-### TODO
-
-- Textures
-- Volumes (like fog)
-- Rectangles
-- Instances
-- Lights
+# Ray Tracer
+
+Building a fully functional ray tracer from scratch based on the "Ray Tracing" series by Peter Shirley.
+
+### In Progress
+
+- Simple brute-force path tracer. 
+
+### TODO
+
+- Textures
+- Volumes (like fog)
+- Rectangles
+- Instances
+- Lights
 - Bounding Volume Hierarchy (BVH).

README.md

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+#include <iostream>
+#include "ray.h"
+// #include "vec.h"
+
+vec3 color(const ray& r)
+{
+	vec3 unit_direction = unit_vector(r.direction());
+	float t = 0.5*(unit_direction.y() + 1.0);
+	return (1.0-t)*vec3(1.0, 1.0, 1.0) + t*vec3(0.5, 0.7, 1.0);
+}
+
+int main()
+{
+	int nx = 200;
+	int ny = 100;
+	std::cout << "P3\n" << nx << " " << ny << "\n255\n";
+	vec3 lower_left_corner(-2.0, -1.0, -1.0);
+	vec3 horizontal(4.0, 0.0, 0.0);
+	vec3 vertical(0.0, 2.0, 0.0);
+	vec3 origin(0.0, 0.0, 0.0);
+	for (int j = ny-1; j >= 0; j--)
+	{
+		for (int i = 0; i < nx; i++)
+		{
+			float u = float(i) / float(nx);
+			float v = float(j) / float(ny);
+			ray r(origin, lower_left_corner + u*horizontal + v*vertical);
+			vec3 col = color(r);
+			int ir = int(255.99*col[0]);
+			int ig = int(255.99*col[1]);
+			int ib = int(255.99*col[2]);
+
+			std::cout << ir << " " << ig << " " << ib << "\n";
+		}
+	}
+}

gen-background

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+#include <iostream>
+#include "vec3.h"
+
+int main()
+{
+	int nx = 200;
+	int ny = 100;
+	std::cout << "P3\n" << nx << " " << ny << "\n255\n";
+	for (int j = ny-1; j >= 0; j--)
+	{
+		for (int i = 0; i < nx; i++)
+		{
+			vec3 col(float(i) / float(nx), float(j) / float(ny), 0.2);
+			int ir = int(255.99*col[0]);
+			int ig = int(255.99*col[1]);
+			int ib = int(255.99*col[2]);
+			std::cout << ir << " " << ig << " " << ib << "\n";
+		}
+	}
+}

gen-background.cpp

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+#include <iostream>
+#include "vec3.h"
+#include "ray.h"
+
+// Find where the ray hit the sphere
+float hit_sphere(const vec3& center, float radius, const ray& r)
+{
+	// Form a quadratic equation to check if the ray satisfies
+	// x*x + y*y + z*z = R*R
+	// which in vector mathematics is
+	// dot((p(t)-c),(p(t)-c))=R*R
+	vec3 oc = r.origin() - center;
+	float a = dot(r.direction(), r.direction());
+	float b = 2.0 * dot(oc, r.direction());
+	float c = dot(oc, oc) - radius*radius;
+	float discriminant = b*b - 4*a*c;
+	// Return the intersection of the ray and the sphere
+	if (discriminant < 0)
+	{
+		return -1.0;
+	}
+	else
+	{
+		return (-b - sqrt(discriminant)) / (2.0*a);
+	}
+}
+
+// Determine the color of the pixel
+vec3 color(const ray& r)
+{
+	// If the ray hits the sphere, find the normal to the sphere
+	// and assign a color according to its direction
+	float t = hit_sphere(vec3(0,0,-1), 0.5, r);
+	if (t > 0.0)
+	{
+		vec3 N = unit_vector(r.point_at_parameter(t) - vec3(0,0,-1));
+		return 0.5*vec3(N.x()+1, N.y()+1, N.z()+1);
+	}
+	// Calculate a blue-white linear interpolation (gradient)
+	// Color the background based on this lerp
+	vec3 unit_direction = unit_vector(r.direction());
+	t = 0.5*(unit_direction.y() + 1.0);
+	return (1.0-t)*vec3(1.0, 1.0, 1.0) + t*vec3(0.5, 0.7, 1.0);
+}
+
+// Print PPM to stdout
+// Pipe to a .ppm file in the terminal to save and view the output
+int main()
+{
+	// Image is 200x100 pixels
+	int nx = 200;
+	int ny = 100;
+	// Standard formatting of a .ppm file
+	std::cout << "P3\n" << nx << " " << ny << "\n255\n";
+	// Start calculations from lower_left_corner
+	vec3 lower_left_corner(-2.0, -1.0, -1.0);
+	// Directional vectors
+	vec3 horizontal(4.0, 0.0, 0.0);
+	vec3 vertical(0.0, 2.0, 0.0);
+	vec3 origin(0.0, 0.0, 0.0);
+	// Color x axis from left to right using index i
+	// Color y axis from top to bottom using index j
+	for (int j = ny-1; j >= 0; j--)
+	{
+		for (int i = 0; i < nx; i++)
+		{
+			float u = float(i) / float(nx);
+			float v = float(j) / float(ny);
+			ray r(origin, lower_left_corner + u*horizontal + v*vertical);
+			vec3 col = color(r);
+			int ir = int(255.99*col[0]);
+			int ig = int(255.99*col[1]);
+			int ib = int(255.99*col[2]);
+
+			std::cout << ir << " " << ig << " " << ib << "\n";
+		}
+	}
+}