BansheeEngine/CamelotUtility/Source/CmSphere.cpp

#include "CmSphere.h"
#include "CmRay.h"
#include "CmPlane.h"
#include "CmAABox.h"

namespace CamelotFramework
{
	std::pair<bool, float> Sphere::intersects(const Ray& ray, bool discardInside) const
	{
		const Vector3& raydir = ray.getDirection();
		// Adjust ray origin relative to sphere center
		const Vector3& rayorig = ray.getOrigin() - getCenter();
		float radius = getRadius();

		// Check origin inside first
		if (rayorig.squaredLength() <= radius*radius && discardInside)
		{
			return std::pair<bool, float>(true, 0.0f);
		}

		// Mmm, quadratics
		// Build coeffs which can be used with std quadratic solver
		// ie t = (-b +/- sqrt(b*b + 4ac)) / 2a
		float a = raydir.dot(raydir);
		float b = 2 * rayorig.dot(raydir);
		float c = rayorig.dot(rayorig) - radius*radius;

		// Calc determinant
		float d = (b*b) - (4 * a * c);
		if (d < 0)
		{
			// No intersection
			return std::pair<bool, float>(false, 0.0f);
		}
		else
		{
			// BTW, if d=0 there is one intersection, if d > 0 there are 2
			// But we only want the closest one, so that's ok, just use the 
			// '-' version of the solver
			float t = ( -b - Math::sqrt(d) ) / (2 * a);
			if (t < 0)
				t = ( -b + Math::sqrt(d) ) / (2 * a);
			return std::pair<bool, float>(true, t);
		}
	}

	bool Sphere::intersects(const Plane& plane) const
	{
		return (Math::abs(plane.getDistance(getCenter())) <= getRadius());
	}

	bool Sphere::intersects(const AABox& box) const
	{
		return box.intersects(*this);
	}
}