/*
 * Copyright (c) 2022, 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) 2014-2022 NVIDIA CORPORATION
 * SPDX-License-Identifier: Apache-2.0
 */

#ifndef RANDOM_GLSL
#define RANDOM_GLSL 1

precision highp float;

// Generate a seed for the random generator.
// Input - pixel.x, pixel.y, frame_nb
// From https://github.com/Cyan4973/xxHash, https://www.shadertoy.com/view/XlGcRh
uint xxhash32(uvec3 p)
{
  const uvec4 primes = uvec4(2246822519U, 3266489917U, 668265263U, 374761393U);
  uint        h32;
  h32 = p.z + primes.w + p.x * primes.y;
  h32 = primes.z * ((h32 << 17) | (h32 >> (32 - 17)));
  h32 += p.y * primes.y;
  h32 = primes.z * ((h32 << 17) | (h32 >> (32 - 17)));
  h32 = primes.x * (h32 ^ (h32 >> 15));
  h32 = primes.y * (h32 ^ (h32 >> 13));
  return h32 ^ (h32 >> 16);
}

//-----------------------------------------------------------------------
// https://www.pcg-random.org/
//-----------------------------------------------------------------------
uint pcg(inout uint state)
{
  uint prev = state * 747796405u + 2891336453u;
  uint word = ((prev >> ((prev >> 28u) + 4u)) ^ prev) * 277803737u;
  state     = prev;
  return (word >> 22u) ^ word;
}

//-----------------------------------------------------------------------
// Generate a random float in [0, 1) given the previous RNG state
//-----------------------------------------------------------------------
float rand(inout uint seed)
{
  uint r = pcg(seed);
  return float(r) * (1.F / float(0xffffffffu));
}


#endif  // RANDOM_GLSL