Ray-AABB (Axis Aligned Bounding Box) intersection.

intersectAABB.glsl

// adapted from intersectCube in https://github.com/evanw/webgl-path-tracing/blob/master/webgl-path-tracing.js

// compute the near and far intersections of the cube (stored in the x and y components) using the slab method
// no intersection means vec.x > vec.y (really tNear > tFar)
vec2 intersectAABB(vec3 rayOrigin, vec3 rayDir, vec3 boxMin, vec3 boxMax) {
    vec3 tMin = (boxMin - rayOrigin) / rayDir;
    vec3 tMax = (boxMax - rayOrigin) / rayDir;
    vec3 t1 = min(tMin, tMax);
    vec3 t2 = max(tMin, tMax);
    float tNear = max(max(t1.x, t1.y), t1.z);
    float tFar = min(min(t2.x, t2.y), t2.z);
    return vec2(tNear, tFar);
};

That type name is absurdly long.