cleanup and refactoring

raytracer/ray_tracing_gltf/shaders/sampling.glsl

@@ -0,0 +1,84 @@
+/*
+ * 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
+ */
+
+// Generate a random unsigned int from two unsigned int values, using 16 pairs
+// of rounds of the Tiny Encryption Algorithm. See Zafar, Olano, and Curtis,
+// "GPU Random Numbers via the Tiny Encryption Algorithm"
+uint tea(uint val0, uint val1)
+{
+  uint v0 = val0;
+  uint v1 = val1;
+  uint s0 = 0;
+
+  for(uint n = 0; n < 16; n++)
+  {
+    s0 += 0x9e3779b9;
+    v0 += ((v1 << 4) + 0xa341316c) ^ (v1 + s0) ^ ((v1 >> 5) + 0xc8013ea4);
+    v1 += ((v0 << 4) + 0xad90777d) ^ (v0 + s0) ^ ((v0 >> 5) + 0x7e95761e);
+  }
+
+  return v0;
+}
+
+// Generate a random unsigned int in [0, 2^24) given the previous RNG state
+// using the Numerical Recipes linear congruential generator
+uint lcg(inout uint prev)
+{
+  uint LCG_A = 1664525u;
+  uint LCG_C = 1013904223u;
+  prev       = (LCG_A * prev + LCG_C);
+  return prev & 0x00FFFFFF;
+}
+
+// Generate a random float in [0, 1) given the previous RNG state
+float rnd(inout uint prev)
+{
+  return (float(lcg(prev)) / float(0x01000000));
+}
+
+
+//-------------------------------------------------------------------------------------------------
+// Sampling
+//-------------------------------------------------------------------------------------------------
+
+// Randomly samples from a cosine-weighted hemisphere oriented in the `z` direction.
+// From Ray Tracing Gems section 16.6.1, "Cosine-Weighted Hemisphere Oriented to the Z-Axis"
+vec3 samplingHemisphere(inout uint seed, in vec3 x, in vec3 y, in vec3 z)
+{
+#define M_PI 3.14159265
+
+  float r1 = rnd(seed);
+  float r2 = rnd(seed);
+  float sq = sqrt(r1);
+
+  vec3 direction = vec3(cos(2 * M_PI * r2) * sq, sin(2 * M_PI * r2) * sq, sqrt(1. - r1));
+  direction      = direction.x * x + direction.y * y + direction.z * z;
+
+  return direction;
+}
+
+// Return the tangent and binormal from the incoming normal
+void createCoordinateSystem(in vec3 N, out vec3 Nt, out vec3 Nb)
+{
+  if(abs(N.x) > abs(N.y))
+    Nt = vec3(N.z, 0, -N.x) / sqrt(N.x * N.x + N.z * N.z);
+  else
+    Nt = vec3(0, -N.z, N.y) / sqrt(N.y * N.y + N.z * N.z);
+  Nb = cross(N, Nt);
+}