Added Sobol matrices as builtins

Author: karimsayedre

examples_tests

@@ -0,0 +1,66 @@
+// Copyright (C) 2018-2026 - DevSH Graphics Programming Sp. z O.O.
+// This file is part of the "Nabla Engine".
+// For conditions of distribution and use, see copyright notice in nabla.h
+#ifndef _NBL_BUILTIN_HLSL_SAMPLING_SOBOL_INCLUDED_
+#define _NBL_BUILTIN_HLSL_SAMPLING_SOBOL_INCLUDED_
+
+#include <nbl/builtin/hlsl/cpp_compat.hlsl>
+#include <nbl/builtin/hlsl/macros.h>
+
+namespace nbl
+{
+namespace hlsl
+{
+namespace sampling
+{
+
+// without acceleration
+struct RowMajorSobolMatrix
+{
+   inline uint16_t operator()(const uint16_t sampleIx)
+   {
+      // max number bits set is 16, if want to mask then need to be 5 apart
+      const uint16_t mask = 0b10000100001u;
+      uint16_t       val  = _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[0] & sampleIx));
+      val |= _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[5] & sampleIx)) << 5;
+      val |= _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[10] & sampleIx)) << 10;
+      val |= _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[15] & sampleIx)) << 15;
+      val &= mask;
+      NBL_UNROLL
+      for (uint16_t i = 1; i < 5; i++)
+      {
+         uint16_t tmp = _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[i] & sampleIx));
+         tmp |= _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[5 + i] & sampleIx)) << 5;
+         tmp |= _static_cast<uint16_t>(spirv::bitCount<uint32_t>(rows[10 + i] & sampleIx)) << 10;
+         val |= (tmp & mask) << i;
+      }
+      return val;
+   }
+
+   uint16_t rows[16];
+};
+
+// bitcount is expensive, its full 32 bit and needs shifting and masking anyway
+struct ColMajorSobolMatrix
+{
+   inline uint16_t operator()(const uint16_t sampleIx)
+   {
+      // abuse 2s completement to get a 0xffffu mask when `sampleIx` bit is on
+      uint16_t val = cols[0] & ((sampleIx & _static_cast<uint16_t>(0x1u)) - _static_cast<uint16_t>(2));
+      NBL_UNROLL
+      for (uint16_t i = 1; i < 16; i++)
+      {
+         const uint16_t mask = _static_cast<uint16_t>(0x1u) << i;
+         val |= cols[i] & ((sampleIx & mask) - _static_cast<uint16_t>(mask + 1));
+      }
+      return val;
+   }
+
+   uint16_t cols[16];
+};
+
+} // namespace sampling
+} // namespace hlsl
+} // namespace nbl
+
+#endif

include/nbl/builtin/hlsl/sampling/sobol.hlsl

@@ -290,6 +290,7 @@ LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/sampling/concepts.hlsl")
 LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/sampling/uniform_spheres.hlsl")
 LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/sampling/alias_table.hlsl")
 LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/sampling/cumulative_probability.hlsl")
+LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/sampling/sobol.hlsl")
 #
 LIST_BUILTIN_RESOURCE(NBL_RESOURCES_TO_EMBED "hlsl/ndarray_addressing.hlsl")
 #