Env map importance sampling #969

kevyuu · 2025-12-19T14:43:32Z

Description

Rework environment map importance sampling to vulkan and hlsl

Testing

Rework example 0 to use vulkan and hlsl

TODO list:

Implement Warpmap Generation in hlsl
Implement Warpmap hierarchical map sampling in hlsl

devshgraphicsprogramming · 2025-12-21T23:50:23Z

include/nbl/builtin/hlsl/concepts/warp.hlsl

+// not the greatest syntax but works
+#define NBL_CONCEPT_PARAM_0 (warp,U)
+#define NBL_CONCEPT_PARAM_1 (uv,float32_t2)
+#define NBL_CONCEPT_PARAM_2 (out,C)


out is a keyword

devshgraphicsprogramming · 2025-12-21T23:50:49Z

include/nbl/builtin/hlsl/concepts/warp.hlsl

+#ifndef _NBL_BUILTIN_HLSL_CONCEPTS_WARP_INCLUDED_
+#define _NBL_BUILTIN_HLSL_CONCEPTS_WARP_INCLUDED_
+
+#include "nbl/builtin/hlsl/concepts/accessors/generic_shared_data.hlsl"
+#include "nbl/builtin/hlsl/fft/common.hlsl"
+
+namespace nbl
+{
+namespace hlsl
+{
+namespace concepts
+{


sampling directory and namespace, then concepts

devshgraphicsprogramming · 2025-12-21T23:52:46Z

include/nbl/builtin/hlsl/concepts/warp.hlsl

+#define uv NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_1
+#define out NBL_CONCEPT_PARAM_T NBL_CONCEPT_PARAM_2
+NBL_CONCEPT_END(
+    ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((a.template warp(uv)) , ::nbl::hlsl::is_same_v, C))


might want to rename uv to xi instead and also require that U has typdefs for xi_type and codomain_type

this will allow you to keep the concept same for warps of cubemaps or 1D functions

also may want to make warp return pair<codomain_type,pdf_type> because there's usually useful data allowing for faster computation fo both quantities than

const auto _out = w.warp(xi); const float pdf = w.backwardDensity(_out);

devshgraphicsprogramming · 2025-12-21T23:53:32Z

include/nbl/builtin/hlsl/sampling/warps/spherical.hlsl

+namespace warp
+{


sampling namespace, anything to do with PDFs is sampling

devshgraphicsprogramming · 2025-12-21T23:54:52Z

include/nbl/builtin/hlsl/warp/spherical.hlsl

+      template <typename C NBL_FUNC_REQUIRES(is_same_v<C, codomain_type>)
+      static float32_t backwardDensity(const C out)
+      {
+        //TODO(kevinyu): Derive this density


1.f/sin(theta) == rsqrt(1.f-C.z*C.z) and you can subsitutre it into same equation as forwardDensity

devshgraphicsprogramming · 2025-12-22T00:00:04Z

include/nbl/builtin/hlsl/concepts/warp.hlsl

+    ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((a.template forwardDensity(uv)) , ::nbl::hlsl::is_same_v, float32_t))
+    ((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((a.template backwardDensity(out)) , ::nbl::hlsl::is_same_v, float32_t))


just thinking, since we'll rewrite our stuff from https://github.com/Devsh-Graphics-Programming/Nabla/blob/master/include/nbl/builtin/hlsl/sampling/cos_weighted_spheres.hlsl into this

we should also add methods called just forward and backward returning quotient_and_pdf each ~~(so we need quotient_type too)~~

Ah wait, this should be for a Sampler, a warp is also a Sampler but has exact quotients, so no RGB possible, the quotient is just the reciprocal of the density.

Sampler concept will be for things like cos_weighted_spheres.

devshgraphicsprogramming · 2025-12-22T00:00:57Z

include/nbl/builtin/hlsl/warp/spherical.hlsl

+      static float32_t forwardDensity(const UV uv)
+      {
+        const float32_t theta = uv.y * numbers::pi<float32_t>;
+        return 1.0f / (sin(theta) * 2 * PI * PI);


why are you using PI from a define!?

devshgraphicsprogramming · 2025-12-22T00:05:15Z

include/nbl/builtin/hlsl/sampling/hierarchical_image.hlsl

+
+class HierarchicalImage 
+{
+  private:


there's no private or public, if you want to indicate something is private, prefix the identifier with __

devshgraphicsprogramming · 2025-12-22T00:05:52Z

include/nbl/builtin/hlsl/sampling/hierarchical_image.hlsl

+    }
+
+  public:
+    template <typename LuminanceAccessor NBL_FUNC_REQUIRES (hierarchical_image::LuminanceReadAccessor<LuminanceAccessor>)


LuminanceAccessor and requires clause goes on HierarchicalImage

devshgraphicsprogramming · 2025-12-22T00:06:59Z

include/nbl/builtin/hlsl/sampling/hierarchical_image.hlsl

+{
+  private:
+
+    static float32_t3 calculateSampleAndPdf(float32_t4 dirsX, float32_t4 dirsY, float32_t2 unnormCoord, uint32_t2 lastWarpmapPixel, NBL_REF_ARG(float32_t) pdf)


things like lastWarpmapPixel go into members, basically you want to store everything that is "constant"/common in members were you to "draw" multiple samples from the same hierarhical image but with different xi

devshgraphicsprogramming · 2025-12-22T00:08:33Z

include/nbl/builtin/hlsl/sampling/hierarchical_image.hlsl

+    template <typename WarpmapAccessor, typename PostWarp NBL_FUNC_REQUIRES(hierarchical_image::WarpmapReadAccessor<WarpmapAccessor>&& Warp<PostWarp, float32_t3>)
+    static float32_t3 sampleWarpmap(NBL_CONST_REF_ARG(WarpmapAccessor) warpmap, const uint32_t2 warpmapSize, const float32_t2 xi, NBL_REF_ARG(float32_t) pdf) {
+
+      // TODO(kevinyu): Add some comment why we substract by 1
+      const uint32_t3 lastWarpmapPixel = warpmapSize - uint32_t3(1, 1, 1);
+
+      const float32_t2 unnormCoord = xi * lastWarpmapPixel;
+      const float32_t2 interpolant = frac(unnormCoord);
+      const float32_t2 warpSampleCoord = (unnormCoord + float32_t2(0.5f, 0.5f)) / float32_t2(warpmapSize.x, warpmapSize.y);
+      const float32_t4 dirsX = warpmap.gatherU(warpSampleCoord);
+      const float32_t4 dirsY = warpmap.gatherV(warpSampleCoord);
+
+      return calculateSampleAndPdf(dirsX, dirsY, unnormCoord, lastWarpmapPixel, pdf);
+
+    }
+
+    template <typename LuminanceAccessor, typename PostWarp NBL_FUNC_REQUIRES(hierarchical_image::LuminanceReadAccessor<LuminanceAccessor>&& Warp<PostWarp, float32_t3>)
+    static float32_t3 sample(NBL_CONST_REF_ARG(LuminanceReadAccessor) luminanceMap, const uint32_t2 lumaMapSize, const bool lumaAspect2x1, const uint32_t2 warpmapSize, const float32_t2 xi, NBL_REF_ARG(float32_t) pdf) {
+
+      const uint32_t3 lastWarpmapPixel = warpmapSize - uint32_t3(1, 1, 1);
+      const float32_t2 unnormCoord = xi * lastWarpmapPixel;
+      const float32_t2 warpSampleCoord = (unnormCoord + float32_t2(0.5f, 0.5f)) / float32_t2(warpmapSize.x, warpmapSize.y);
+      const float32_t2 dir0 = binarySearch(luminanceMap, lumaMapSize, warpSampleCoord + float32_t2(0, 1), lumaAspect2x1);
+      const float32_t2 dir1 = binarySearch(luminanceMap, lumaMapSize, warpSampleCoord + float32_t2(1, 1), lumaAspect2x1);
+      const float32_t2 dir2 = binarySearch(luminanceMap, lumaMapSize, warpSampleCoord + float32_t2(1, 0), lumaAspect2x1);
+      const float32_t2 dir3 = binarySearch(luminanceMap, lumaMapSize, warpSampleCoord, lumaAspect2x1);
+
+      const float32_t4 dirsX = float32_t4(dir0.x, dir1.x, dir2.x, dir3.x);
+      const float32_t4 dirsY = float32_t4(dir1.y, dir1.y, dir2.y, dir3.y);
+
+      return calculateSampleAndPdf(dirsX, dirsY, unnormCoord, lastWarpmapPixel, pdf);
+
+    }


split the ground truth binary search hierarchical image sampler and the approximate warp map hierarchical image sampler into two separate classes

kevyuu added 9 commits November 11, 2025 15:50

Fix small bug in GenericDataAccessor definition

b99ae6e

First draft of Warpmap Generation workgroup implementation

b9537ea

Add warp concept

a737173

Add spherical warp

64349db

Remove envmap accessors.hlsl

e44fcf4

Hierarchical image sampling implementation

9b29dfd

Merge branch 'master' into env_map_importance_sampling

06ae3e4

Merge branch 'master' into env_map_importance_sampling

16ecb52

Remove envmap.hlsl

8d682b9

devshgraphicsprogramming reviewed Dec 21, 2025

View reviewed changes

devshgraphicsprogramming reviewed Dec 22, 2025

View reviewed changes

kevyuu added 3 commits December 22, 2025 23:59

Move to sampling namespace and implement backward density

890f7c6

Remove private, public from hierarchical_image

f99c63b

Refactor hierarchical image to keep accessor and common data as member

3ff2791

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Env map importance sampling #969

Env map importance sampling #969

kevyuu commented Dec 19, 2025

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		((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((a.template forwardDensity(uv)) , ::nbl::hlsl::is_same_v, float32_t))
		((NBL_CONCEPT_REQ_EXPR_RET_TYPE)((a.template backwardDensity(out)) , ::nbl::hlsl::is_same_v, float32_t))

Env map importance sampling #969

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Env map importance sampling #969

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kevyuu commented Dec 19, 2025

Description

Testing

TODO list:

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