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// Copyright (c) 2004-2008 AGEIA Technologies, Inc. All rights reserved.
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#include "foundation/PxVec3.h"
#include "GuIntersectionRaySphere.h"
#include "GuIntersectionRay.h"

using namespace physx;

// Based on GD Mag code, but now works correctly when origin is inside the sphere.
// This version has limited accuracy.
bool Gu::intersectRaySphereBasic(const PxVec3& origin, const PxVec3& dir, PxReal length, const PxVec3& center, PxReal radius, PxReal& dist, PxVec3* hit_pos)
{
	// get the offset vector
	const PxVec3 offset = center - origin;

	// get the distance along the ray to the center point of the sphere
	const PxReal ray_dist = dir.dot(offset);

	// get the squared distances
	const PxReal off2 = offset.dot(offset);
	const PxReal rad_2 = radius * radius;
	if(off2 <= rad_2)
	{
		// we're in the sphere
		if(hit_pos)
			*hit_pos	= origin;
		dist	= 0.0f;
		return true;
	}

	if(ray_dist <= 0 || (ray_dist - length) > radius)
	{
		// moving away from object or too far away
		return false;
	}

	// find hit distance squared
	const PxReal d = rad_2 - (off2 - ray_dist * ray_dist);
	if(d<0.0f)
	{
		// ray passes by sphere without hitting
		return false;
	}

	// get the distance along the ray
	dist = ray_dist - PxSqrt(d);
	if(dist > length)
	{
		// hit point beyond length
		return false;
	}

	// sort out the details
	if(hit_pos)
		*hit_pos = origin + dir * dist;
	return true;
}

// PT: modified version calls the previous function, but moves the ray origin closer to the sphere. The test accuracy is
// greatly improved as a result. This is an idea proposed on the GD-Algorithms list by Eddie Edwards.
// See: http://www.codercorner.com/blog/?p=321
bool Gu::intersectRaySphere(const PxVec3& origin, const PxVec3& dir, PxReal length, const PxVec3& center, PxReal radius, PxReal& dist, PxVec3* hit_pos)
{
	const PxVec3 x = origin - center;
	PxReal l = PxSqrt(x.dot(x)) - radius - GU_RAY_SURFACE_OFFSET;

//	if(l<0.0f)
//		l=0.0f;
	l = physx::intrinsics::selectMax(l, 0.0f);

	bool status = intersectRaySphereBasic(origin + l*dir, dir, length - l, center, radius, dist, hit_pos);
	if(status)
	{
//		dist += l/length;
		dist += l;
	}
	return status;
}
