bool intersectRay( const Box3f& box,
const Vector3f& rayOrigin, const Vector3f& rayDirection,
float& tIntersect, float tMin )
{
assert( box.isStandard() );
assert( !box.isEmpty() );
float tNear;
float tFar;
bool intersect = intersectLine( box, rayOrigin, rayDirection,
tNear, tFar );
if( intersect )
{
if( tNear >= tMin )
{
tIntersect = tNear;
}
else if( tFar >= tMin )
{
tIntersect = tFar;
}
else
{
intersect = false;
}
}
return intersect;
}
bool intersectLine( const Box3f& box,
const Vector3f& rayOrigin, const Vector3f& rayDirection,
float& tNear, float& tFar )
{
assert( box.isStandard() );
assert( !box.isEmpty() );
// Compute t to each face.
Vector3f rcpDir = 1.0f / rayDirection;
// Three "bottom" faces (min of the box).
Vector3f tBottom = rcpDir * ( box.origin - rayOrigin );
// three "top" faces (max of the box)
Vector3f tTop = rcpDir * ( box.rightTopFront() - rayOrigin );
// find the smallest and largest distances along each axis
Vector3f tMin = libcgt::core::math::minimum( tBottom, tTop );
Vector3f tMax = libcgt::core::math::maximum( tBottom, tTop );
// tNear is the largest tMin
tNear = libcgt::core::math::maximum( tMin );
// tFar is the smallest tMax
tFar = libcgt::core::math::minimum( tMax );
return tFar > tNear;
}
bool carefulIntersectBoxRay( const Box3f& box,
const Vector3f& rayOrigin, const Vector3f& rayDirection,
float& t0, float& t1, int& t0Face, int& t1Face,
float rayTMin, float rayTMax )
{
assert( box.isStandard() );
assert( !box.isEmpty() );
t0 = rayTMin;
t1 = rayTMax;
t0Face = -1;
t1Face = -1;
// Compute t to each face.
Vector3f rcpDir = 1.0f / rayDirection;
Vector3f boxMax = box.rightTopFront();
for( int i = 0; i < 3; ++i )
{
// Compute the intersection between the line and the slabs along the
// i-th axis, parameterized as [tNear, tFar].
float rcpDir = 1.0f / rayDirection[ i ];
float tNear = rcpDir * ( box.origin[ i ] - rayOrigin[ i ] );
float tFar = rcpDir * ( boxMax[ i ] - rayOrigin[ i ] );
// Which face we're testing against.
int nearFace = 2 * i;
int farFace = 2 * i + 1;
// Swap such that tNear < tFAr.
if( tNear > tFar )
{
std::swap( tNear, tFar );
std::swap( nearFace, farFace );
}
// Compute the set intersection between [tNear, tFar] and [t0, t1].
if( tNear > t0 )
{
t0 = tNear;
t0Face = nearFace;
}
if( tFar < t1 )
{
t1 = tFar;
t1Face = farFace;
}
// Early abort if the range is empty.
if( t0 > t1 )
{
return false;
}
}
return true;
}
Vector3f clamp( const Vector3f& v, const Box3f& box )
{
assert( box.isStandard() );
return
{
clampToRangeInclusive( v.x, box.left(), box.right() ),
clampToRangeInclusive( v.y, box.bottom(), box.top() ),
clampToRangeInclusive( v.z, box.back(), box.front() )
};
}