/*
 * 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 "gltf.glsl"
#include "raycommon.glsl"
#include "sampling.glsl"
#include "host_device.h"

hitAttributeEXT vec2 attribs;

// clang-format off
layout(location = 0) rayPayloadInEXT hitPayload prd;
layout(location = 1) rayPayloadEXT bool isShadowed;

layout(set = 0, binding = 0 ) uniform accelerationStructureEXT topLevelAS;
layout(set = 0, binding = 2) readonly buffer _InstanceInfo {PrimMeshInfo primInfo[];};


layout(buffer_reference, scalar) readonly buffer Vertices  { vec3  v[]; };
layout(buffer_reference, scalar) readonly buffer Indices   { ivec3 i[]; };
layout(buffer_reference, scalar) readonly buffer Normals   { vec3  n[]; };
layout(buffer_reference, scalar) readonly buffer TexCoords { vec2  t[]; };
layout(buffer_reference, scalar) readonly buffer Materials { GltfShadeMaterial m[]; };

layout(set = 1, binding = eSceneDesc ) readonly buffer SceneDesc_ { SceneDesc sceneDesc; };
layout(set = 1, binding = eTextures) uniform sampler2D texturesMap[]; // all textures

layout(push_constant) uniform _PushConstantRay { PushConstantRay pcRay; };
// clang-format on


void main()
{
  // Retrieve the Primitive mesh buffer information
  PrimMeshInfo pinfo = primInfo[gl_InstanceCustomIndexEXT];

  // Getting the 'first index' for this mesh (offset of the mesh + offset of the triangle)
  uint indexOffset  = (pinfo.indexOffset / 3) + gl_PrimitiveID;
  uint vertexOffset = pinfo.vertexOffset;           // Vertex offset as defined in glTF
  uint matIndex     = max(0, pinfo.materialIndex);  // material of primitive mesh

  Materials gltfMat   = Materials(sceneDesc.materialAddress);
  Vertices  vertices  = Vertices(sceneDesc.vertexAddress);
  Indices   indices   = Indices(sceneDesc.indexAddress);
  Normals   normals   = Normals(sceneDesc.normalAddress);
  TexCoords texCoords = TexCoords(sceneDesc.uvAddress);
  Materials materials = Materials(sceneDesc.materialAddress);

  // Getting the 3 indices of the triangle (local)
  ivec3 triangleIndex = indices.i[indexOffset];
  triangleIndex += ivec3(vertexOffset);  // (global)

  const vec3 barycentrics = vec3(1.0 - attribs.x - attribs.y, attribs.x, attribs.y);

  // Vertex of the triangle
  const vec3 pos0           = vertices.v[triangleIndex.x];
  const vec3 pos1           = vertices.v[triangleIndex.y];
  const vec3 pos2           = vertices.v[triangleIndex.z];
  const vec3 position       = pos0 * barycentrics.x + pos1 * barycentrics.y + pos2 * barycentrics.z;
  const vec3 world_position = vec3(gl_ObjectToWorldEXT * vec4(position, 1.0));

  // Normal
  const vec3 nrm0         = normals.n[triangleIndex.x];
  const vec3 nrm1         = normals.n[triangleIndex.y];
  const vec3 nrm2         = normals.n[triangleIndex.z];
  vec3       normal       = normalize(nrm0 * barycentrics.x + nrm1 * barycentrics.y + nrm2 * barycentrics.z);
  const vec3 world_normal = normalize(vec3(normal * gl_WorldToObjectEXT));
  const vec3 geom_normal  = normalize(cross(pos1 - pos0, pos2 - pos0));

  // TexCoord
  const vec2 uv0       = texCoords.t[triangleIndex.x];
  const vec2 uv1       = texCoords.t[triangleIndex.y];
  const vec2 uv2       = texCoords.t[triangleIndex.z];
  const vec2 texcoord0 = uv0 * barycentrics.x + uv1 * barycentrics.y + uv2 * barycentrics.z;

  // https://en.wikipedia.org/wiki/Path_tracing
  // Material of the object
  GltfShadeMaterial mat       = materials.m[matIndex];
  vec3              emittance = mat.emissiveFactor;

  // Pick a random direction from here and keep going.
  vec3 tangent, bitangent;
  createCoordinateSystem(world_normal, tangent, bitangent);
  vec3 rayOrigin    = world_position;
  vec3 rayDirection = samplingHemisphere(prd.seed, tangent, bitangent, world_normal);

  const float cos_theta = dot(rayDirection, world_normal);
  // Probability density function of samplingHemisphere choosing this rayDirection
  const float p = cos_theta / M_PI;

  // Compute the BRDF for this ray (assuming Lambertian reflection)
  vec3 albedo = mat.pbrBaseColorFactor.xyz;
  if(mat.pbrBaseColorTexture > -1)
  {
    uint txtId = mat.pbrBaseColorTexture;
    albedo *= texture(texturesMap[nonuniformEXT(txtId)], texcoord0).xyz;
  }
  vec3 BRDF = albedo / M_PI;

  prd.rayOrigin    = rayOrigin;
  prd.rayDirection = rayDirection;
  prd.hitValue     = emittance;
  prd.weight       = BRDF * cos_theta / p;
  return;

  // Recursively trace reflected light sources.
  if(prd.depth < 10)
  {
    prd.depth++;
    float tMin  = 0.001;
    float tMax  = 100000000.0;
    uint  flags = gl_RayFlagsOpaqueEXT;
    traceRayEXT(topLevelAS,    // acceleration structure
                flags,         // rayFlags
                0xFF,          // cullMask
                0,             // sbtRecordOffset
                0,             // sbtRecordStride
                0,             // missIndex
                rayOrigin,     // ray origin
                tMin,          // ray min range
                rayDirection,  // ray direction
                tMax,          // ray max range
                0              // payload (location = 0)
    );
  }
  vec3 incoming = prd.hitValue;

  // Apply the Rendering Equation here.
  prd.hitValue = emittance + (BRDF * incoming * cos_theta / p);
}