//SPDX-License-Identifier: MIT
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

#version 460
#extension GL_EXT_ray_tracing : enable

// RTVolume intersection shader — runs once per AABB the ray enters
// (VK_RAY_TRACING_SHADER_GROUP_TYPE_PROCEDURAL_HIT_GROUP_KHR). Analytic
// ray-sphere test: the unit box [-1,1]^3 built by Mesh::BuildProcedural
// is treated as the bounding volume of a radius-1 sphere centred at the
// object origin. The object-space ray is NOT normalised (it is
// worldToObject * worldRay), so the reported t is directly comparable to
// the world-space ray parameter — solve the quadratic with the general
// a = dot(d,d) form rather than assuming |d| == 1. Mirrors
// intersection.wgsl on the WebGPU path.

hitAttributeEXT vec2 attribs;

void main() {
    vec3  oc = gl_ObjectRayOriginEXT;          // sphere centre is the origin
    vec3  d  = gl_ObjectRayDirectionEXT;
    float a  = dot(d, d);
    float b  = 2.0 * dot(oc, d);
    float c  = dot(oc, oc) - 1.0;              // radius 1
    float disc = b * b - 4.0 * a * c;
    if (disc < 0.0) return;

    float sq = sqrt(disc);
    float t  = (-b - sq) / (2.0 * a);                       // near root
    if (t < gl_RayTminEXT) t = (-b + sq) / (2.0 * a);       // fall back to far root
    if (t < gl_RayTminEXT || t > gl_RayTmaxEXT) return;

    attribs = vec2(0.0);
    reportIntersectionEXT(t, 0u);
}