Handle random seed generation better for PerlinNoise
Before, the result of `time` was used for the RNG. This change uses `std::random_device` for a better seed when possible.
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@ -149,7 +149,26 @@ private:
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VTKM_CONT void GeneratePermutations()
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{
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std::mt19937_64 rng;
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rng.seed(this->Seed);
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if (this->Seed != 0)
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{
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rng.seed(this->Seed);
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}
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else
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{
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// If a seed has not been chosen, create a unique seed here. It is done here instead
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// of the `PerlinNoise` source constructor for 2 reasons. First, `std::random_device`
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// can be slow. If the user wants to specify a seed, it makes no sense to spend
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// time generating a random seed only to overwrite it. Second, creating the seed
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// here allows subsequent runs of the `PerlinNoise` source to have different random
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// results if a seed is not specified.
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//
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// It is also worth noting that the current time is added to the random number.
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// This is because the spec for std::random_device allows it to be deterministic
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// if nondeterministic hardware is unavailable and the deterministic numbers can
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// be the same for every execution of the program. Adding the current time is
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// a fallback for that case.
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rng.seed(std::random_device{}() + time(NULL));
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}
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std::uniform_int_distribution<vtkm::IdComponent> distribution(0, this->TableSize - 1);
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vtkm::cont::ArrayHandle<vtkm::Id> perms;
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@ -179,11 +198,6 @@ namespace vtkm
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namespace source
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{
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PerlinNoise::PerlinNoise()
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: Seed(static_cast<vtkm::IdComponent>(time(NULL)))
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{
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}
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PerlinNoise::PerlinNoise(vtkm::Id3 dims)
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: PerlinNoise()
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{
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@ -29,7 +29,7 @@ namespace source
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class VTKM_SOURCE_EXPORT PerlinNoise final : public vtkm::source::Source
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{
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public:
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VTKM_CONT PerlinNoise();
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VTKM_CONT PerlinNoise() = default;
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VTKM_CONT ~PerlinNoise() = default;
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VTKM_CONT PerlinNoise(const PerlinNoise&) = default;
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@ -55,6 +55,9 @@ public:
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VTKM_CONT vtkm::Vec3f GetOrigin() const { return this->Origin; }
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VTKM_CONT void SetOrigin(const vtkm::Vec3f& origin) { this->Origin = origin; }
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/// \brief The seed used for the pseudorandom number generation of the noise.
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///
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/// If the seed is set to 0, then a new, unique seed is picked each time `Execute` is run.
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VTKM_CONT vtkm::IdComponent GetSeed() const { return this->Seed; }
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VTKM_CONT void SetSeed(vtkm::IdComponent seed) { this->Seed = seed; }
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@ -63,7 +66,7 @@ private:
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vtkm::Id3 PointDimensions = { 16, 16, 16 };
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vtkm::Vec3f Origin = { 0, 0, 0 };
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vtkm::IdComponent Seed;
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vtkm::IdComponent Seed = 0;
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};
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} //namespace source
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} //namespace vtkm
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