Envmap sampling test by kevyuu · Pull Request #257 · Devsh-Graphics-Programming/Nabla-Examples-and-Tests

kevyuu · 2026-02-23T15:07:30Z

This is pull request for testing environment map sampling

devshgraphicsprogramming · 2026-02-25T13:53:52Z

75_EnvmapImportanceSamplingTest/app_resources/common.hlsl

+using namespace nbl;
+using namespace nbl::hlsl;
+
+NBL_CONSTEXPR uint32_t WorkgroupSize = 128;


64 to be more representative of path tracing workloads

devshgraphicsprogramming · 2026-02-25T13:55:07Z

75_EnvmapImportanceSamplingTest/CMakeLists.txt

+include(common RESULT_VARIABLE RES)
+if(NOT RES)
+	message(FATAL_ERROR "common.cmake not found. Should be in {repo_root}/cmake directory")
+endif()
+
+nbl_create_executable_project("" "" "" "" "${NBL_EXECUTABLE_PROJECT_CREATION_PCH_TARGET}")
+
+if(NBL_EMBED_BUILTIN_RESOURCES)
+	set(_BR_TARGET_ ${EXECUTABLE_NAME}_builtinResourceData)
+	set(RESOURCE_DIR "app_resources")
+
+	get_filename_component(_SEARCH_DIRECTORIES_ "${CMAKE_CURRENT_SOURCE_DIR}" ABSOLUTE)
+	get_filename_component(_OUTPUT_DIRECTORY_SOURCE_ "${CMAKE_CURRENT_BINARY_DIR}/src" ABSOLUTE)
+	get_filename_component(_OUTPUT_DIRECTORY_HEADER_ "${CMAKE_CURRENT_BINARY_DIR}/include" ABSOLUTE)
+
+    file(GLOB_RECURSE BUILTIN_RESOURCE_FILES RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}/${RESOURCE_DIR}" CONFIGURE_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/${RESOURCE_DIR}/*")
+    foreach(RES_FILE ${BUILTIN_RESOURCE_FILES})
+      LIST_BUILTIN_RESOURCE(RESOURCES_TO_EMBED "${RES_FILE}")
+    endforeach()
+
+	ADD_CUSTOM_BUILTIN_RESOURCES(${_BR_TARGET_} RESOURCES_TO_EMBED "${_SEARCH_DIRECTORIES_}" "${RESOURCE_DIR}" "nbl::this_example::builtin" "${_OUTPUT_DIRECTORY_HEADER_}" "${_OUTPUT_DIRECTORY_SOURCE_}")
+
+	LINK_BUILTIN_RESOURCES_TO_TARGET(${EXECUTABLE_NAME} ${_BR_TARGET_})
+endif() 
+
+add_dependencies(${EXECUTABLE_NAME} argparse)
+target_include_directories(${EXECUTABLE_NAME} PUBLIC $<TARGET_PROPERTY:argparse,INTERFACE_INCLUDE_DIRECTORIES>)
+


@AnastaZIuk review and okay the CMake

devshgraphicsprogramming · 2026-03-25T16:33:46Z

75_EnvmapImportanceSamplingTest/app_resources/test.comp.hlsl

+    uint32_t2 uv = texelCoord / float32_t2(pc.warpWidth, pc.warpHeight);
+    const float32_t4 reds = warpMap.GatherRed(warpSampler, uv);
+    const float32_t4 greens = warpMap.GatherGreen(warpSampler, uv);
+


youre corner sampling, so you need to add half a pixel to texelCoord when you make texelCoord out of it before the frac

Right now you're gathering the wrong pixels - for the same floor(texelCoord) you're getting different values from your gather

it would actually make sense to pull this logic out of the warpmap accessor, and have the warpmap accessor just report the size of the warpmap and let the Warpmap sampler deal with corner sampling and computing the interpolant while this function would just take uint16_t coord instead of xi and interpolant arguments

devshgraphicsprogramming · 2026-03-25T17:18:31Z

75_EnvmapImportanceSamplingTest/main.cpp

+	template<typename T>
+	bool checkEq(T a, T b, float32_t eps = 1e-4)
+	{
+		if constexpr (!is_vector_v<T>)
+		{
+			return abs(a - b) <= eps;
+		}
+		else
+		{
+			T _a = hlsl::max(hlsl::abs(a), hlsl::promote<T>(1e-5));
+			T _b = hlsl::max(hlsl::abs(b), hlsl::promote<T>(1e-5));
+			return nbl::hlsl::all<hlsl::vector<bool, vector_traits<T>::Dimension> >(nbl::hlsl::max<T>(_a / _b, _b / _a) <= hlsl::promote<T>(1 + eps));
+		}
+	}


master has a good version of this

devshgraphicsprogramming · 2026-03-25T17:21:32Z

75_EnvmapImportanceSamplingTest/main.cpp

+
+		auto shader = IAsset::castDown<IShader>(assets[0]);
+		return shader;
+	};


@AnastaZIuk do we have a nice thing for this in the example commons ?

Esp if it could also use the driver to compile shaders that aren't yet compiled

devshgraphicsprogramming · 2026-03-25T17:24:21Z

75_EnvmapImportanceSamplingTest/app_resources/test.comp.hlsl

+  const sample_type sample = hImage.generate(xi);
+  const float3 L = sample.value();
+
+  float eps_x = pc.eps;
+  float eps_y = pc.eps;
+
+  const sample_type sample_plus_du = hImage.generate(xi + float32_t2(0.5f * eps_x, 0));
+  const float3 L_plus_du = sample_plus_du.value();
+  const sample_type sample_plus_dv = hImage.generate(xi + float32_t2(0, 0.5f * eps_y));
+  const float3 L_plus_dv = sample_plus_dv.value();
+
+  const sample_type sample_minus_du = hImage.generate(xi - float32_t2(0.5f * eps_x, 0));
+  const float3 L_minus_du = sample_minus_du.value();
+  const sample_type sample_minus_dv = hImage.generate(xi - float32_t2(0, 0.5f * eps_y));
+  const float3 L_minus_dv = sample_minus_dv.value();
+
+  float jacobian = length(cross(L_plus_du - L_minus_du, L_plus_dv - L_minus_dv)) / (eps_x * eps_y);
+
+  TestOutput testOutput;
+  testOutput.L = L;
+  testOutput.jacobian = jacobian;
+  testOutput.pdf = sample.pdf();


sample is a HLSL keyword, use _sample instead

devshgraphicsprogramming · 2026-03-25T22:47:38Z

75_EnvmapImportanceSamplingTest/app_resources/test.comp.hlsl

+  float eps_y = pc.eps;
+
+  const sample_type sample_plus_du = hImage.generate(xi + float32_t2(0.5f * eps_x, 0));
+  const float3 L_plus_du = sample_plus_du.value();


when PR 1001 comes, you'll be getting these via forwardPdf then it will be useful to test that backwardPdf matches if the WarpSamplerT is BackwardTractableSampler

In either case you'll want to test that forwardWeight == backwardWeight

devshgraphicsprogramming · 2026-03-26T00:12:26Z

75_EnvmapImportanceSamplingTest/app_resources/test.comp.hlsl

+  using direct_hierarchical_image_type = sampling::HierarchicalWarpSampler<float, LuminanceAccessor, sampling::warp::Spherical<float> >;
+
+  float32_t eps = pc.eps;
+
+  random::PCG32 pcg = random::PCG32::construct(threadID.x);
+  uint32_t2 xi_uint = random::DimAdaptorRecursive<random::PCG32, 2>::__call(pcg);
+
+  float32_t2 xi = convertToFloat01(xi_uint);
+
+  xi.x = hlsl::clamp(xi.x, eps, 1.f - eps);
+  xi.y = hlsl::clamp(xi.y, eps, 1.f - eps);
+
+  test_sample_t testSample;
+  testSample.xi = xi;
+
+  uint32_t2 warpResolution = { pc.warpWidth, pc.warpHeight };
+  const direct_hierarchical_image_type directHImage = direct_hierarchical_image_type::create(luminanceAccessor, pc.avgLuma, warpResolution, warpResolution.x != warpResolution.y);
+
+  testSample.directOutput = GenerateTestOutput(directHImage, xi);
+
+  using cached_hierarchical_image_type = sampling::WarpmapSampler<float, LuminanceAccessor, WarpmapAccessor, sampling::warp::Spherical<float> >;


the Spherical warp you're using, is not aware of the corner sampling, so the hierarchical sampler outputs uv for corner sampling and you're warping them like regular UVs

see https://github.com/Devsh-Graphics-Programming/Nabla/pull/969/changes#r2991772100

ok as long as you make the HierarchicalWarpGenerator (to be renamed HierarchicalSampler) handle all the corner sampling for you transparently and return and accept corner sampled as [0,1]^2 relative to the corners, this can stay as is in the examples

devshgraphicsprogramming · 2026-03-26T00:32:02Z

75_EnvmapImportanceSamplingTest/app_resources/test.comp.hlsl

+    const float32_t4 reds = warpMap.GatherRed(warpSampler, uv);
+    const float32_t4 greens = warpMap.GatherGreen(warpSampler, uv);


how does this even compile? HLSL GatherRed takes a sampler object and then a floating point coordinate

so the / float32_t2(pc.warpWidth, pc.warpHeight) division shouldn't be there

kevyuu added 2 commits February 23, 2026 21:07

Add example 75

766d965

Fix filename logging

b3e27cb

kevyuu mentioned this pull request Feb 23, 2026

Env map importance sampling Devsh-Graphics-Programming/Nabla#969

Open

devshgraphicsprogramming reviewed Feb 25, 2026

View reviewed changes

Update unit test to comply with latest envmap pr

b474907

devshgraphicsprogramming reviewed Mar 25, 2026

View reviewed changes

devshgraphicsprogramming reviewed Mar 26, 2026

View reviewed changes

		const float32_t4 reds = warpMap.GatherRed(warpSampler, uv);
		const float32_t4 greens = warpMap.GatherGreen(warpSampler, uv);

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kevyuu commented Feb 23, 2026

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devshgraphicsprogramming Mar 25, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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devshgraphicsprogramming Mar 25, 2026 •

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