Add unit tests for PdfSampler

Author: otto-link

tests/src/test_pdf_sampler.cpp

@@ -0,0 +1,148 @@
+#include <gtest/gtest.h>
+
+#include "highmap.hpp"
+
+using namespace hmap;
+
+TEST(PdfSampler, SampleReturnsValueInUnitInterval)
+{
+  std::vector<float> pdf = {1.f, 1.f, 1.f, 1.f};
+
+  PdfSampler sampler(pdf, 42);
+
+  for (int i = 0; i < 1000; ++i)
+  {
+    float s = sampler.sample();
+
+    EXPECT_GE(s, 0.f);
+    EXPECT_LT(s, 1.f);
+  }
+}
+
+TEST(PdfSampler, SampleVectorSize)
+{
+  std::vector<float> pdf = {1.f, 2.f, 3.f};
+
+  PdfSampler sampler(pdf, 42);
+
+  std::vector<float> samples = sampler.sample(128);
+
+  EXPECT_EQ(samples.size(), 128);
+}
+
+TEST(PdfSampler, DeterministicWithSameSeed)
+{
+  std::vector<float> pdf = {1.f, 2.f, 3.f, 4.f};
+
+  PdfSampler s0(pdf, 1234);
+  PdfSampler s1(pdf, 1234);
+
+  for (int i = 0; i < 100; ++i)
+  {
+    float a = s0.sample();
+    float b = s1.sample();
+
+    EXPECT_FLOAT_EQ(a, b);
+  }
+}
+
+TEST(PdfSampler, DifferentSeedsProduceDifferentSequences)
+{
+  std::vector<float> pdf = {1.f, 2.f, 3.f, 4.f};
+
+  PdfSampler s0(pdf, 1);
+  PdfSampler s1(pdf, 2);
+
+  bool different = false;
+
+  for (int i = 0; i < 50; ++i)
+  {
+    if (s0.sample() != s1.sample())
+    {
+      different = true;
+      break;
+    }
+  }
+
+  EXPECT_TRUE(different);
+}
+
+TEST(PdfSampler, UniformPdfProducesUniformBins)
+{
+  std::vector<float> pdf = {1.f, 1.f, 1.f, 1.f};
+
+  PdfSampler sampler(pdf, 42);
+
+  const int nsamples = 20000;
+
+  std::vector<int> bins(4, 0);
+
+  for (int i = 0; i < nsamples; ++i)
+  {
+    float s = sampler.sample();
+
+    int k = std::min(3, static_cast<int>(s * 4.f));
+
+    bins[k]++;
+  }
+
+  float expected = static_cast<float>(nsamples) / 4.f;
+
+  for (int c : bins)
+    EXPECT_NEAR(static_cast<float>(c), expected, 0.1f * expected);
+}
+
+TEST(PdfSampler, WeightedPdfFavorsLargerBins)
+{
+  std::vector<float> pdf = {1.f, 1.f, 10.f, 1.f};
+
+  PdfSampler sampler(pdf, 42);
+
+  const int nsamples = 20000;
+
+  std::vector<int> bins(4, 0);
+
+  for (int i = 0; i < nsamples; ++i)
+  {
+    float s = sampler.sample();
+
+    int k = std::min(3, static_cast<int>(s * 4.f));
+
+    bins[k]++;
+  }
+
+  EXPECT_GT(bins[2], bins[0]);
+  EXPECT_GT(bins[2], bins[1]);
+  EXPECT_GT(bins[2], bins[3]);
+}
+
+TEST(PdfSampler, SingleBinAlwaysSamplesInsideBin)
+{
+  std::vector<float> pdf = {1.f};
+
+  PdfSampler sampler(pdf, 42);
+
+  for (int i = 0; i < 100; ++i)
+  {
+    float s = sampler.sample();
+
+    EXPECT_GE(s, 0.f);
+    EXPECT_LT(s, 1.f);
+  }
+}
+
+TEST(PdfSampler, SampleVectorDeterministic)
+{
+  std::vector<float> pdf = {1.f, 2.f, 3.f};
+
+  PdfSampler s0(pdf, 99);
+  PdfSampler s1(pdf, 99);
+
+  std::vector<float> v0 = s0.sample(256);
+  std::vector<float> v1 = s1.sample(256);
+
+  ASSERT_EQ(v0.size(), v1.size());
+
+  for (size_t i = 0; i < v0.size(); ++i)
+    EXPECT_FLOAT_EQ(v0[i], v1[i]);
+}