Sphere (#8)

Author: karnkaul

tray/CMakeLists.txt

@@ -1,13 +1,16 @@
 add_executable(${PROJECT_NAME})
 target_include_directories(${PROJECT_NAME} PRIVATE src)
 target_sources(${PROJECT_NAME} PRIVATE
+  src/tray/hit.cpp
+  src/tray/hit.hpp
   src/tray/image.cpp
   src/tray/image.hpp
   src/tray/io.cpp
   src/tray/io.hpp
   src/tray/nvec3.hpp
   src/tray/ray.hpp
   src/tray/rgb.hpp
+  src/tray/sphere.hpp
   src/tray/vec.hpp
   src/tray/viewport.hpp
 

tray/src/main.cpp

@@ -1,3 +1,4 @@
+#include <tray/hit.hpp>
 #include <tray/image.hpp>
 #include <tray/io.hpp>
 #include <tray/ray.hpp>
@@ -18,13 +19,19 @@ int main() {
 
 	static constexpr fvec3 gradient[] = {Rgb::from_hex(0xffffff).to_f32(), Rgb::from_hex(0x002277).to_f32()};
 	auto image = Image{extent};
+	auto const sphere = Sphere{.centre = {0.0f, 0.0f, -5.0f}, .radius = 1.0f};
 
 	for (std::uint32_t row = 0; row < image.extent().y(); ++row) {
 		auto const yt = static_cast<float>(row) / static_cast<float>(image.extent().y() - 1);
 		for (std::uint32_t col = 0; col < image.extent().x(); ++col) {
 			auto const xt = static_cast<float>(col) / static_cast<float>(image.extent().x() - 1);
 			auto const dir = top_left + xt * horizontal - yt * vertical - origin;
 			auto const ray = Ray{origin, dir};
+			auto hit = Hit{};
+			if (hit(ray, sphere)) {
+				image[{row, col}] = Rgb::from_f32(0.5f * (hit.normal.vec() + 1.0f));
+				continue;
+			}
 			auto const t = 0.5f * (ray.direction.vec().y() + 1.0f);
 			image[{row, col}] = Rgb::from_f32(lerp(gradient[0], gradient[1], t));
 		}

tray/src/tray/hit.cpp

@@ -0,0 +1,29 @@
+#include <tray/hit.hpp>
+#include <span>
+
+namespace tray {
+namespace {
+constexpr float smallet_positive_root(std::span<float const, 2> roots) {
+	if (roots[0] < 0.0f) { return roots[1]; }
+	if (roots[1] < 0.0f) { return roots[0]; }
+	return std::min(roots[0], roots[1]);
+}
+} // namespace
+
+bool Hit::operator()(Ray const& ray, Sphere const& sphere) {
+	auto const co = ray.origin - sphere.centre;
+	float const b = 2.0f * dot(ray.direction.vec(), co);
+	float const c = dot(co, co) - sphere.radius * sphere.radius;
+	float const discriminant = b * b - 4 * c;
+	if (discriminant < 0.0f) { return false; }
+
+	auto const sqd = std::sqrt(discriminant);
+	float const roots[] = {0.5f * (-b - sqd), 0.5f * (-b + sqd)};
+	auto const t = smallet_positive_root(roots);
+	if (t < 0.0f) { return false; }
+
+	point = ray.at(t);
+	normal = point - sphere.centre;
+	return true;
+}
+} // namespace tray

tray/src/tray/hit.hpp

@@ -0,0 +1,13 @@
+#pragma once
+#include <tray/nvec3.hpp>
+#include <tray/ray.hpp>
+#include <tray/sphere.hpp>
+
+namespace tray {
+struct Hit {
+	fvec3 point{};
+	nvec3 normal{};
+
+	bool operator()(Ray const& ray, Sphere const& sphere);
+};
+} // namespace tray

tray/src/tray/sphere.hpp

@@ -0,0 +1,9 @@
+#pragma once
+#include <tray/vec.hpp>
+
+namespace tray {
+struct Sphere {
+	fvec3 centre{};
+	float radius{};
+};
+} // namespace tray