1 files changed, 81 insertions, 0 deletions
diff --git a/sphere.h b/sphere.h
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+++ b/sphere.h
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+//
+// Created by Keuin on 2022/4/12.
+//
+
+#ifndef RT_SPHERE_H
+#define RT_SPHERE_H
+
+#include "object.h"
+#include "hitlist.h"
+#include "viewport.h"
+#include "timer.h"
+#include "bitmap.h"
+#include "ray.h"
+#include "vec.h"
+#include <cstdlib>
+#include <memory>
+#include <limits>
+#include <vector>
+#include <iostream>
+#include <cstdint>
+
+class sphere : public object {
+    vec3d center;
+    double radius;
+
+public:
+    sphere() = delete;
+
+    sphere(const vec3d &center, 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);
+    }
+};
+
+#endif //RT_SPHERE_H