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//
// Created by Keuin on 2022/4/11.
//
#include <cstdint>
#include <iostream>
#include <vector>
#include <limits>
#include <memory>
#include <cstdlib>
#include "vec.h"
#include "ray.h"
#include "bitmap.h"
#include "timer.h"
#define DEMO_BALL
class object {
public:
// Will the given ray hit. Returns time t if hits in range [t1, t2].
virtual bool hit(const ray3d &r, double &t, double t1, double t2) const = 0;
// With t2 = infinity
inline bool hit(const ray3d &r, double &t, double t1) const {
return hit(r, t, t1, std::numeric_limits<double>::infinity());
}
// Given a point on the surface, returns the normalized outer normal vector on that point.
virtual vec3d normal_vector(const vec3d &where) const = 0;
// object color, currently not parameterized
virtual pixel8b color() const = 0;
// subclasses must have virtual destructors
virtual ~object() = default;
};
class sphere : public object {
vec3d center;
double radius;
public:
sphere() = delete;
sphere(const vec3d ¢er, double radius) : center(center), radius(radius) {}
~sphere() override = default;
vec3d normal_vector(const vec3d &where) const override {
// We assume the point is on surface, speeding up the normalization
return (where - center) / radius;
}
bool hit(const ray3d &r, double &t, double t1, double t2) const override {
// Ray: {Source, Direction, time}
// Sphere: {Center, radius}
// sphere hit formula: |Source + Direction * time - Center| = radius
// |(Sx + Dx * t - Cx, Sy + Dy * t - Cy, Sz + Dz * t - Cz)| = radius
const auto c2s = r.source() - center; // center to source
// A = D dot D
const double a = r.direction().mod2();
// H = (S - C) dot D
const auto h = dot(c2s, r.direction());
// B = 2H ( not used in our optimized routine )
// C = (S - C) dot (S - C) - radius^2
const double c = c2s.mod2() - radius * radius;
// 4delta = H^2 - AC
// delta_q = H^2 - AC (quarter delta)
const double delta_q = h * h - a * c;
bool hit = false;
if (delta_q >= 0) {
// return the root in range [t1, t2]
// t = ( -H +- sqrt{ delta_q } ) / A
double root;
root = (-h - sqrt(delta_q)) / a;
if (root >= t1 && root <= t2) {
hit = true;
t = root;
} else {
root = (-h + sqrt(delta_q)) / a;
if (root >= t1 && root <= t2) {
hit = true;
t = root;
}
}
}
return hit;
}
pixel8b color() const override {
return pixel8b::from_normalized(1.0, 0.0, 0.0);
}
};
class viewport {
double half_width, half_height; // viewport size
vec3d center; // coordinate of the viewport center point
std::vector<std::shared_ptr<object>> objects; // TODO move to world class
// Given a ray from the camera, generate a color the camera seen on the viewport.
pixel8b color(const ray3d &r) {
// Detect hits
bool hit = false;
double hit_t = std::numeric_limits<double>::infinity();
std::shared_ptr<object> hit_obj;
// Check the nearest object we hit
for (const auto &obj: objects) {
double t_;
if (obj->hit(r, t_, 0.0) && t_ < hit_t) {
hit = true;
hit_t = t_;
hit_obj = obj;
}
}
if (hit) {
// normal vector on hit point
const auto nv = hit_obj->normal_vector(r.at(hit_t));
// return obj->color();
// visualize normal vector at hit point
return pixel8b::from_normalized(nv);
}
// Does not hit anything. Get background color (infinity)
const auto u = (r.direction().y + 1.0) * 0.5;
return mix(
pixel8b::from_normalized(1.0, 1.0, 1.0),
pixel8b::from_normalized(0.5, 0.7, 1.0),
1.0 - u,
u
);
}
public:
viewport() = delete;
viewport(double width, double height, vec3d viewport_center) :
half_width(width / 2.0), half_height(height / 2.0), center(viewport_center) {}
// Add an object to the world.
void add_object(std::shared_ptr<object> &&obj) {
objects.push_back(std::move(obj));
}
// Generate the image seen on given viewpoint.
bitmap8b render(vec3d viewpoint, uint16_t image_width, uint16_t image_height) {
bitmap8b image{image_width, image_height};
const auto r = center - viewpoint;
const int img_hw = image_width / 2, img_hh = image_height / 2;
// iterate over every pixel on the image
for (int j = -img_hh + 1; j <= img_hh; ++j) { // axis y, transformation is needed
for (int i = -img_hw; i < img_hw; ++i) { // axis x
const vec3d off{
.x=1.0 * i / img_hw * half_width,
.y=1.0 * j / img_hh * half_height,
.z=0.0
}; // offset on screen plane
const auto dir = r + off; // direction vector from camera to current pixel on screen
const ray3d ray{viewpoint, dir}; // from camera to pixel (on the viewport)
const auto pixel = color(ray);
image.set(i + img_hw, -j + img_hh, pixel);
}
}
return image;
}
};
void generate_image(uint16_t image_width, uint16_t image_height, double viewport_width, double focal_length,
double sphere_z, double sphere_r) {
double r = 1.0 * image_width / image_height;
viewport vp{viewport_width, viewport_width / r, vec3d{0, 0, -focal_length}};
vp.add_object(std::make_shared<sphere>(
vec3d{0, -100.5, -1},
100)); // the earth
vp.add_object(std::make_shared<sphere>(vec3d{0, 0, sphere_z}, sphere_r));
timer tm;
tm.start_measure();
const auto image = vp.render(vec3d::zero(), image_width, image_height); // camera position as the coordinate origin
tm.stop_measure();
if (!std::getenv("NOPRINT")) {
image.write_plain_ppm(std::cout);
} else {
std::cerr << "NOPRINT is defined. PPM Image won't be printed." << std::endl;
}
}
int main(int argc, char **argv) {
if (argc != 7) {
printf("Usage: %s <image_width> <image_height> <viewport_width> <focal_length> <sphere_z> <sphere_r>\n",
argv[0]);
return 0;
}
std::string iw{argv[1]}, ih{argv[2]}, vw{argv[3]}, fl{argv[4]}, sz{argv[5]}, sr{argv[6]};
generate_image(std::stoul(iw), std::stoul(ih),
std::stod(vw), std::stod(fl),
std::stod(sz), std::stod(sr));
}
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