udQuad.glsl

float dot2( in vec3 v ) { return dot(v,v); }
float udQuad( vec3 p, vec3 a, vec3 b, vec3 c, vec3 d )
{
    vec3 ba = b - a; vec3 pa = p - a;
    vec3 cb = c - b; vec3 pb = p - b;
    vec3 dc = d - c; vec3 pc = p - c;
    vec3 ad = a - d; vec3 pd = p - d;
    vec3 nor = cross( ba, ad );

    return sqrt(
    (sign(dot(cross(ba,nor),pa)) +
     sign(dot(cross(cb,nor),pb)) +
     sign(dot(cross(dc,nor),pc)) +
     sign(dot(cross(ad,nor),pd))<3.0)
     ?
     min( min( min(
     dot2(ba*clamp(dot(ba,pa)/dot2(ba),0.0,1.0)-pa),
     dot2(cb*clamp(dot(cb,pb)/dot2(cb),0.0,1.0)-pb) ),
     dot2(dc*clamp(dot(dc,pc)/dot2(dc),0.0,1.0)-pc) ),
     dot2(ad*clamp(dot(ad,pd)/dot2(ad),0.0,1.0)-pd) )
     :
     dot(nor,pa)*dot(nor,pa)/dot2(nor) );
}

#pragma glslify: export(udQuad)