Created a new example to test the compilation and concepts of samplers by karimsayedre · Pull Request #252 · Devsh-Graphics-Programming/Nabla-Examples-and-Tests

karimsayedre · 2026-02-18T20:09:58Z

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37_HLSLSamplingTests/app_resources/test_compile.comp.hlsl

CMakeLists.txt

…hader permutation), configurable work group size in `ITester`

…omplete tests

devshgraphicsprogramming · 2026-03-23T13:12:02Z

Everything looks good, although it would be nice to try the CDF and Alias table samples at several different PoT sizes from 8 to 128*1024^2 to find the perf crossover point across sizes

Also do a 1 Reservoir sampling from size of 2 to 32 because that will likely be faster than CDF and Alias at really small sizes (same way linear search is vs binary and hashmap due to caching effects)

devshgraphicsprogramming · 2026-03-23T13:20:44Z

Also see if you can address any of the open comments in the BxDF testing PR
#236

devshgraphicsprogramming · 2026-03-27T21:31:33Z

31_HLSLPathTracer/app_resources/hlsl/next_event_estimator.hlsl


-        pdf = rcpPdf > numeric_limits<scalar_type>::min ? (1.0 / rcpPdf) : numeric_limits<scalar_type>::max;
+        const scalar_type fwdPdf = pst.forwardPdf(pstCache);
+        pdf = fwdPdf < numeric_limits<scalar_type>::max ? fwdPdf : numeric_limits<scalar_type>::max;


this does nothing

devshgraphicsprogramming · 2026-03-27T21:32:20Z

37_HLSLSamplingTests/app_resources/common/array_accessor.hlsl

+	using value_type = T;
+	template<typename V, typename I>
+	void get(I i, NBL_REF_ARG(V) val) NBL_CONST_MEMBER_FUNC { val = V(data[i]); }
+	T operator[](uint32_t i) NBL_CONST_MEMBER_FUNC { return data[i]; }


what do you need operator[] for ?

devshgraphicsprogramming · 2026-03-27T21:34:26Z

37_HLSLSamplingTests/app_resources/common/bilinear.hlsl

-
-		float32_t2 diff = input.u - output.inverted;
-		output.roundtripError = nbl::hlsl::length(diff);
-		output.jacobianProduct = (float32_t(1.0) / output.forwardPdf) * output.backwardPdf;


even if you're no longer 100% bijective in all cases, you can perturb input.u by epsillon and work out the Jacobian * forwardPdf and compare against 1

devshgraphicsprogramming · 2026-03-27T21:35:42Z

37_HLSLSamplingTests/app_resources/common/linear.hlsl

-			sampling::Linear<float32_t>::cache_type cache;
-			output.generateInversed = _sampler.generateInverse(output.generated);
 			output.backwardPdf = _sampler.backwardPdf(output.generated);
 		}
-		output.roundtripError = abs(input.u - output.generateInversed);
-		output.jacobianProduct = (float32_t(1.0) / output.forwardPdf) * output.backwardPdf;


same as bilinear

devshgraphicsprogramming · 2026-03-27T21:36:21Z

37_HLSLSamplingTests/app_resources/common/projected_sphere.hlsl

-		{
-			sampling::ProjectedSphere<float32_t>::cache_type cache;
-			output.inverted = sampler.generateInverse(output.generated);
-			output.backwardPdf = sampler.backwardPdf(output.generated);
-		}
-		float32_t2 xyDiff = output.modifiedU.xy - output.inverted.xy;
-		output.roundtripError = nbl::hlsl::length(xyDiff);
-		output.jacobianProduct = (float32_t(1.0) / output.forwardPdf) * output.backwardPdf;


you can still work out a Jacobian from perturbing u

only for the hemisphere I guess

devshgraphicsprogramming · 2026-03-27T21:37:42Z

37_HLSLSamplingTests/app_resources/common/projected_spherical_triangle.hlsl

 			sampling::ProjectedSphericalTriangle<float32_t>::cache_type cache;
 			output.generated = sampler.generate(input.u, cache);
-			output.cachedPdf = cache.pdf;
 			output.forwardPdf = sampler.forwardPdf(cache);


you can do a JAcobian test, since its bijective if you wanted to

devshgraphicsprogramming · 2026-03-27T21:39:25Z

37_HLSLSamplingTests/app_resources/common/spherical_triangle.hlsl

 			output.inverted = sampler.generateInverse(output.generated);
 			// Backward: evaluate pdf at generated point (no cache needed)
 			output.backwardPdf = sampler.backwardPdf(output.generated);


differentiated generateInverse Jacobian determinant should equal the PDF I think

while differentiated generate multiplied with PDF comes out to 1

devshgraphicsprogramming · 2026-03-27T21:40:37Z

37_HLSLSamplingTests/app_resources/common/box_muller_transform.hlsl

 		}

 		output.backwardPdf = sampler.backwardPdf(output.generated);
 		output.separateBackwardPdf = sampler.separateBackwardPdf(output.generated);


you can test a lot of things, like:

separate/independent PDF multiplying together to give the scalar PDF
2 Jacobian test follows PDF

devshgraphicsprogramming · 2026-03-27T21:44:04Z

37_HLSLSamplingTests/app_resources/spherical_rectangle_test.comp.hlsl

+   const float32_t toFloat = asfloat(0x2f800004u);
+   uint32_t2 acc = (uint32_t2)0;
+   uint32_t accPdf = 0;
+   for (uint32_t i = 0u; i < uint32_t(BENCH_ITERS); i++)
+   {
+      float32_t2 u = float32_t2(rng(), rng()) * toFloat;
+      sampling::SphericalRectangle<float32_t>::cache_type cache;
+      acc ^= asuint(sampler.generate(u, cache));
+      accPdf ^= asuint(sampler.forwardPdf(cache));
+   }


you need two benchmark modes, multiple samples from same create and multiple samples with create (to measure set-up overhead)

first one matters only for rejection sampling or multisampling, second one is more real use case when you only draw 1 NEE sample per path vertex so the create to generate ratio is 1:1

# Conflicts: # common/include/nbl/examples/Tester/ITester.h

Created an new example to test the compilation and concepts of samplers

ebf25f4

karimsayedre mentioned this pull request Feb 18, 2026

Created concepts for samplers, added quotient_and_pdf variants to satisfy the concepts Devsh-Graphics-Programming/Nabla#1001

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devshgraphicsprogramming reviewed Feb 19, 2026

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devshgraphicsprogramming requested a review from AnastaZIuk February 19, 2026 14:12

devshgraphicsprogramming reviewed Feb 19, 2026

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karimsayedre added 11 commits February 25, 2026 09:14

changed example number to 37

18fe5eb

Tests using ITester, Benchmarking using the same testing shaders (s…

d1fa476

…hader permutation), configurable work group size in `ITester`

Merge branch 'master' into sampler-concepts

d8a6e9b

Merge branch 'master' into sampler-concepts

6740883

fixes after merge

4a45531

Samplers now conform to concepts, benchmarks for all samplers, more c…

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…omplete tests

added alias table and cumulative probablility testing and benchmarks

d9f4907

Merge branch 'master' into sampler-concepts

69fe759

minor formatting changes

8f3c1c9

addressed comments in concepts.hlsl, making sure 37 and 66 work

24baa87

renamed InvertableSampler to BackwardTracableSampler

54acb0c

karimsayedre added 3 commits March 23, 2026 17:36

Merge branch 'master' into sampler-concepts-upd

f94133f

formatting to 3 spaces, added pipeline info report

60e0a35

addressed more comments, made benchmarks more fair

b33f66a

devshgraphicsprogramming reviewed Mar 27, 2026

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karimsayedre added 5 commits March 28, 2026 18:00

Merge branch 'master' into sampler-concepts

f76b427

# Conflicts: # common/include/nbl/examples/Tester/ITester.h

changed forwardPdf to take the codomain as an arg

ff397d0

test code reduction in main.cpp

cfefa02

Merge branch 'master' into sampler-concepts

d93a0f8

forwardPdf should take domain not codomain, also corrected some comments

eb10cf2

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devshgraphicsprogramming commented Mar 23, 2026 •

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