raytrace.rint

/*
 * Copyright (c) 2019-2021, NVIDIA CORPORATION.  All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * SPDX-FileCopyrightText: Copyright (c) 2019-2021 NVIDIA CORPORATION
 * SPDX-License-Identifier: Apache-2.0
 */

#version 460
#extension GL_EXT_ray_tracing : require
#extension GL_EXT_nonuniform_qualifier : enable
#extension GL_EXT_scalar_block_layout : enable
#extension GL_GOOGLE_include_directive : enable
#extension GL_EXT_shader_explicit_arithmetic_types_int64 : require
#extension GL_EXT_buffer_reference2 : require
#include "raycommon.glsl"
#include "wavefront.glsl"


layout(set = 1, binding = eImplicit, scalar) buffer allSpheres_
{
  Sphere allSpheres[];
};


struct Ray
{
  vec3 origin;
  vec3 direction;
};

// Ray-Sphere intersection
// http://viclw17.github.io/2018/07/16/raytracing-ray-sphere-intersection/
float hitSphere(const Sphere s, const Ray r)
{
  vec3  oc           = r.origin - s.center;
  float a            = dot(r.direction, r.direction);
  float b            = 2.0 * dot(oc, r.direction);
  float c            = dot(oc, oc) - s.radius * s.radius;
  float discriminant = b * b - 4 * a * c;
  if(discriminant < 0)
  {
    return -1.0;
  }
  else
  {
    return (-b - sqrt(discriminant)) / (2.0 * a);
  }
}

// Ray-AABB intersection
float hitAabb(const Aabb aabb, const Ray r)
{
  vec3  invDir = 1.0 / r.direction;
  vec3  tbot   = invDir * (aabb.minimum - r.origin);
  vec3  ttop   = invDir * (aabb.maximum - r.origin);
  vec3  tmin   = min(ttop, tbot);
  vec3  tmax   = max(ttop, tbot);
  float t0     = max(tmin.x, max(tmin.y, tmin.z));
  float t1     = min(tmax.x, min(tmax.y, tmax.z));
  return t1 > max(t0, 0.0) ? t0 : -1.0;
}

void main()
{
  Ray ray;
  ray.origin    = gl_WorldRayOriginEXT;
  ray.direction = gl_WorldRayDirectionEXT;

  // Sphere data
  Sphere sphere = allSpheres[gl_PrimitiveID];

  float tHit    = -1;
  int   hitKind = gl_PrimitiveID % 2 == 0 ? KIND_SPHERE : KIND_CUBE;
  if(hitKind == KIND_SPHERE)
  {
    // Sphere intersection
    tHit = hitSphere(sphere, ray);
  }
  else
  {
    // AABB intersection
    Aabb aabb;
    aabb.minimum = sphere.center - vec3(sphere.radius);
    aabb.maximum = sphere.center + vec3(sphere.radius);
    tHit         = hitAabb(aabb, ray);
  }

  // Report hit point
  if(tHit > 0)
    reportIntersectionEXT(tHit, hitKind);
}