Add vector on sphere generation

libs/pcg/include/psemek/pcg/random/vector_sphere.hpp

@@ -0,0 +1,101 @@
+#pragma once
+
+#include <psemek/geom/vector.hpp>
+#include <psemek/geom/constants.hpp>
+
+#include <random>
+
+namespace psemek::pcg
+{
+
+	template <typename T, std::size_t N>
+	struct uniform_sphere_vector_distribution
+	{
+		std::normal_distribution<T> d;
+		T r;
+
+		uniform_sphere_vector_distribution(T r = T{1})
+			: r{r}
+		{}
+
+		template <typename RNG>
+		auto operator()(RNG && rng)
+		{
+			geom::vector<T, N> v;
+			while (true)
+			{
+				for (std::size_t i = 0; i < N; ++i)
+					v[i] = d(rng);
+
+				T l = length(v);
+				if (l != T{})
+					return v / l * r;
+			}
+		}
+	};
+
+	template <typename T>
+	struct uniform_sphere_vector_distribution<T, 1>
+	{
+		std::uniform_int_distribution<int> d{0, 1};
+		T r;
+
+		uniform_sphere_vector_distribution(T r = T{1})
+			: r{r}
+		{}
+
+		template <typename RNG>
+		geom::vector<T, 1> operator()(RNG && rng)
+		{
+			if (d(rng) == 0)
+				return {r};
+			return {-r};
+		}
+	};
+
+	template <typename T>
+	struct uniform_sphere_vector_distribution<T, 2>
+	{
+		std::uniform_real_distribution<T> d{0, 2 * geom::pi};
+		T r;
+
+		uniform_sphere_vector_distribution(T r = T{1})
+			: r{r}
+		{}
+
+		template <typename RNG>
+		geom::vector<T, 2> operator()(RNG && rng)
+		{
+			T a = d(rng);
+			return {r * std::cos(a), r * std::sin(a)};
+		}
+	};
+
+	template <typename T>
+	struct uniform_sphere_vector_distribution<T, 3>
+	{
+		std::uniform_real_distribution<T> d{-1, 1};
+		T r;
+
+		uniform_sphere_vector_distribution(T r = T{1})
+			: r{r}
+		{}
+
+		template <typename RNG>
+		auto operator()(RNG && rng)
+		{
+			geom::vector<T, 3> v;
+			while (true)
+			{
+				for (std::size_t i = 0; i < 3; ++i)
+					v[i] = d(rng);
+
+				T l = length(v);
+
+				if (l <= T{1})
+					return v / l * r;
+			}
+		}
+	};
+
+}