eic-opticks/CSG/csg_intersect_leaf_plane.h

0001 #pragma once
0002
0003 LEAF_FUNC
0004 float distance_leaf_plane( const float3& pos, const quad& q0 )
0005 {
0006     const float3 n = make_float3(q0.f.x, q0.f.y, q0.f.z) ;   // plane normal direction
0007     const float d = q0.f.w ;                                 // distance to origin
0008     float pn = dot(pos, n );
0009     float sd = pn - d ;
0010     return sd ;
0011 }
0012
0013
0014 /**
0015 intersect_leaf_plane
0016 -----------------------
0017
0018 * https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-plane-and-ray-disk-intersection
0019
0020 Equation for points p that are in the plane::
0021
0022    (p - p0).n = 0
0023
0024    p0   : point in plane which is pointed to by normal n vector from origin,
0025    p-p0 : vector that lies within the plane, and hence is perpendicular to the normal direction
0026    p0.n : d, distance from plane to origin
0027
0028
0029    p = o + t v   : parametric ray equation
0030
0031    (o + t v - p0).n = 0
0032
0033    (p0-o).n  = t v.n
0034
0035             (p0 - o).n        d - o.n
0036        t  = -----------  =   -----------
0037                v.n              v.n
0038
0039
0040 Special case example :
0041
0042 * for rays within XZ plane what is the z-coordinate at which rays cross the x=0 "line" ?
0043
0044
0045                 :
0046                 :    Z
0047                 :    |
0048                 p0   +--X
0049                /:
0050               / :
0051              /  :
0052             /   :
0053            /    :
0054           +     :
0055          o     x=0
0056
0057
0058          plane normal  [-1, 0, 0]
0059
0060     t0 = -o.x/v.x
0061     z0 =  o.z + t0*v.z
0062
0063 **/
0064
0065 LEAF_FUNC
0066 void intersect_leaf_plane( bool& valid_isect, float4& isect, const quad& q0, const float t_min, const float3& ray_origin, const float3& ray_direction )
0067 {
0068    const float3 n = make_float3(q0.f.x, q0.f.y, q0.f.z) ;   // plane normal direction
0069    const float d = q0.f.w ;                                 // distance to origin
0070
0071    float idn = 1.f/dot(ray_direction, n );
0072    float on = dot(ray_origin, n );
0073
0074    float t_cand = (d - on)*idn ;
0075
0076    bool valid_isect = t_cand > t_min ;
0077    if( valid_isect )
0078    {
0079        isect.x = n.x ;
0080        isect.y = n.y ;
0081        isect.z = n.z ;
0082        isect.w = t_cand ;
0083    }
0084 }
0085
0086
0087