Geometric Tests - 3D Math Primer for Graphics and Game Development - page 741

Woo [72] describes a method that first determines which side of the
box would be intersected and then performs a ray-plane intersection test
against the plane containing that side. If the point of intersection with the
plane is within the box, then there is an intersection; otherwise, there is no
intersection. This is implemented in Listing A.6.

/ / R e t u r n p a r a m e t r i c p o i n t o f i n t e r s e c t i o n 0 . . . 1 , o r a r e a l l y huge

/ / number i f no i n t e r s e c t i o n i s found

f l o a t AABB3 : : r a y I n t e r s e c t (
c o n s t V e c t o r 3 &r a y O r g , / / o r g i n o f t h e r a y

c o n s t V e c t o r 3 &r a y D e l t a , / / l e n g t h and d i r e c t i o n o f t h e r a y

∗ r e t u r n N o r m a l

V e c t o r 3 / / o p t i o n a l l y , t h e normal i s r e t u r n e d

) c o n s t {

/ / We ' l l r e t u r n t h i s huge number i f no i n t e r s e c t i o n

c o n s t f l o a t k N o I n t e r s e c t i o n = FLT MAX ;

/ / Check f o r p o i n t i n s i d e box , t r i v i a l r e j e c t , and

/ / d e t e r m i n e p a r a m e t r i c d i s t a n c e t o each f r o n t f a c e

bool i n s i d e = t r u e ;

f l o a t x t , xn ;

i f ( r a y O r g . x < min . x ) {

x t = min . x − r a y O r g . x ;

i f ( x t > r a y D e l t a . x ) r e t u r n k N o I n t e r s e c t i o n ;

x t / = r a y D e l t a . x ;

i n s i d e = f a l s e ;

xn = − 1.0 f ;

} e l s e i f ( r a y O r g . x > max . x ) {

x t = max . x − r a y O r g . x ;

i f ( x t < r a y D e l t a . x ) r e t u r n k N o I n t e r s e c t i o n ;

x t / = r a y D e l t a . x ;

i n s i d e = f a l s e ;

xn = 1 . 0 f ;

} e l s e {

x t = − 1.0 f ;

}

f l o a t y t , yn ;

i f ( r a y O r g . y < min . y ) {

y t = min . y − r a y O r g . y ;

i f ( y t > r a y D e l t a . y ) r e t u r n k N o I n t e r s e c t i o n ;

y t / = r a y D e l t a . y ;

i n s i d e = f a l s e ;

− 1.0 f ;

yn =

}

( r a y O r g . y > max . y )

{

e l s e i f

y t = max . y − r a y O r g . y ;

i f ( y t < r a y D e l t a . y ) r e t u r n k N o I n t e r s e c t i o n ;

y t / = r a y D e l t a . y ;

i n s i d e = f a l s e ;

yn = 1 . 0 f ;

} e l s e {

y t = − 1.0 f ;

}

f l o a t z t , zn ;

i f ( r a y O r g . z < min . z ) {

z t = min . z − r a y O r g . z ;

i f ( z t > r a y D e l t a . z ) r e t u r n k N o I n t e r s e c t i o n ;

z t / = r a y D e l t a . z ;