Move Sphere::does_intersect to object_sphere; fill out object_sphere in C++

src/object.cc

@@ -6,9 +6,9 @@
  */
 
 
-#include <assert.h>
-#include <math.h>
-#include <stdlib.h>
+#include <cassert>
+#include <cmath>
+#include <cstdlib>
 
 #include "basics.h"
 #include "object.h"
@@ -48,24 +48,22 @@ Object::set_origin(Vector3 v)
 }
 
 /*
- * sphere_does_intersect --
+ * Sphere::does_intersect --
  *
- * Compute the intersection of a ray with the given object. The object must be a Sphere. All intersection t values are
- * returned in the **t argument. The number of values returned therein is indicated by the return value. Memory is
- * allocated at *t. It is the caller's responsibility to free it when it is no longer needed. If 0 is returned, no
- * memory needs to be freed.
+ * Compute the intersection of a ray with this Sphere. All intersection t values are returned in the **t argument. The
+ * number of values returned therein is indicated by the return value. Memory is allocated at *t. It is the caller's
+ * responsibility to free it when it is no longer needed. If 0 is returned, no memory needs to be freed.
  */
 int
-sphere_does_intersect(Object *obj, Ray ray, float **t)
+Sphere::does_intersect(const Ray &ray, float **t)
 {
-    // Location of the vector in object space.
-    Vector3 ray_loc_obj = vector_sub_vector(ray.location, object_get_location(obj));
-    float r = object_sphere_get_radius(obj);
+    // Origin of the vector in object space.
+    Vector3 ray_origin_obj = ray.origin - get_origin();
 
     // Coefficients for quadratic equation.
-    float a = vector_dot(ray.direction, ray.direction);
-    float b = vector_dot(ray.direction, ray_loc_obj) * 2.0;
-    float c = vector_dot(ray_loc_obj, ray_loc_obj) - (r * r);
+    float a = ray.direction.dot(ray.direction);
+    float b = ray.direction.dot(ray_origin_obj) * 2.0;
+    float c = ray_origin_obj.dot(ray_origin_obj) - (radius * radius);
 
     // Discriminant for the quadratic equation.
     float discrim = (b * b) - (4.0 * a * c);
@@ -100,13 +98,15 @@ sphere_does_intersect(Object *obj, Ray ray, float **t)
      * store the required number of values.
      */
     int nints = (t0 != t1) ? 2 : 1;
-    *t = malloc(sizeof(float) * nints);
-    if (*t == NULL) {
-        return 0;
-    }
-    (*t)[0] = t0;
-    if (nints > 1) {
-        (*t)[1] = t1;
+    if (t != NULL) {
+        *t = malloc(sizeof(float) * nints);
+        if (*t == NULL) {
+            return 0;
+        }
+        (*t)[0] = t0;
+        if (nints > 1) {
+            (*t)[1] = t1;
+        }
     }
 
     return nints;

src/object_sphere.cc

@@ -0,0 +1,165 @@
+/* object_sphere.h
+ *
+ * Spheres are Scene objects defined by a center point and a radius.
+ *
+ * Eryn Wells <eryn@erynwells.me>
+ */
+
+#include <assert.h>
+#include <math.h>
+#include <stdlib.h>
+
+#include "object.h"
+#include "object_sphere.h"
+
+
+/*
+ * Sphere::Sphere --
+ *
+ * Default constructor. Create a Sphere with radius 1.0.
+ */
+Sphere::Sphere()
+    : Sphere(1.0)
+{ }
+
+
+/*
+ * Sphere::Sphere --
+ *
+ * Constructor. Create a Sphere with the given radius.
+ */
+Sphere::Sphere(float r)
+    : Sphere(Vector3::Zero, r)
+{ }
+
+
+Sphere::Sphere(Vector3 o, float r)
+    : Object(o),
+      float(r)
+{ }
+
+
+/*
+ * Sphere::get_radius --
+ * Sphere::set_radius --
+ *
+ * Get and set the radius of this Sphere.
+ */
+float
+Sphere::get_radius()
+{
+    return radius;
+}
+
+void
+Sphere::set_radius(float r)
+{
+    radius = (radius >= 0.0) ? r : -r;
+}
+
+
+/*
+ * Sphere::does_intersect --
+ *
+ * Compute the intersection of a ray with this Sphere. All intersection t values are returned in the **t argument. The
+ * number of values returned therein is indicated by the return value. Memory is allocated at *t. It is the caller's
+ * responsibility to free it when it is no longer needed. If 0 is returned, no memory needs to be freed.
+ */
+int
+Sphere::does_intersect(const Ray &ray, float **t)
+{
+    // Origin of the vector in object space.
+    Vector3 ray_origin_obj = ray.origin - get_origin();
+
+    // Coefficients for quadratic equation.
+    float a = ray.direction.dot(ray.direction);
+    float b = ray.direction.dot(ray_origin_obj) * 2.0;
+    float c = ray_origin_obj.dot(ray_origin_obj) - (radius * radius);
+
+    // Discriminant for the quadratic equation.
+    float discrim = (b * b) - (4.0 * a * c);
+
+    // If the discriminant is less than zero, there are no real (as in not imaginary) solutions to this intersection.
+    if (discrim < 0) {
+        return 0;
+    }
+
+    // Compute the intersections, the roots of the quadratic equation. Spheres have at most two intersections.
+    float sqrt_discrim = sqrtf(discrim);
+    float t0 = (-b - sqrt_discrim) / (2.0 * a);
+    float t1 = (-b + sqrt_discrim) / (2.0 * a);
+
+    // If t[1] is less than t[0], swap them (t[0] will always be the first intersection).
+    if (t1 < t0) {
+        float tmp = t0;
+        t0 = t1;
+        t1 = tmp;
+    }
+
+    /*
+     * If the farther intersection of the two is in the negative direction, the sphere is in the ray's negative
+     * direction.
+     */
+    if (t1 < 0) {
+        return 0;
+    }
+
+    /*
+     * Allocate the memory and store the values. It's possible the two values are equal. Only allocate enough memory to
+     * store the required number of values.
+     */
+    int nints = (t0 != t1) ? 2 : 1;
+    if (t != NULL) {
+        *t = malloc(sizeof(float) * nints);
+        if (*t == NULL) {
+            return 0;
+        }
+        (*t)[0] = t0;
+        if (nints > 1) {
+            (*t)[1] = t1;
+        }
+    }
+
+    return nints;
+}
+
+
+/*
+ * sphere_point_lies_on_surface --
+ *
+ * Determine if a point lies on the given sphere.
+ */
+int
+sphere_point_lies_on_surface(Object *obj, Vector3 p)
+{
+    assert(obj != NULL && object_get_type(obj) == ObjectTypeSphere);
+
+    Vector3 loc = object_get_location(obj);
+    float x = p.x - loc.x;
+    float y = p.y - loc.y;
+    float z = p.z - loc.z;
+    float r = object_sphere_get_radius(obj);
+
+    return (x * x) + (y * y) + (z * z) == (r * r);
+}
+
+
+/*
+ * sphere_compute_normal --
+ *
+ * Compute the normal for the given Object (which must be a Sphere) at the given point. This point must lie on the
+ * surface of the object.
+ */
+/* static */ Vector3
+sphere_compute_normal(Object *obj, Vector3 p)
+{
+    assert(obj != NULL && object_get_type(obj) == ObjectTypeSphere);
+
+    // Make sure the given point is actually on the surface of the sphere.
+    if (!sphere_point_lies_on_surface(obj, p)) {
+        return Vector3Zero;
+    }
+
+    // The fun thing about sphere is the normal to any point on the sphere is the point itself. Woo!
+    return p;
+}