Add RandomNumberGenerator::rand_weighted method

core/math/random_number_generator.cpp

@@ -42,6 +42,7 @@ void RandomNumberGenerator::_bind_methods() {
  ClassDB::bind_method(D_METHOD("randfn", "mean", "deviation"), &RandomNumberGenerator::randfn, DEFVAL(0.0), DEFVAL(1.0));
  ClassDB::bind_method(D_METHOD("randf_range", "from", "to"), &RandomNumberGenerator::randf_range);
  ClassDB::bind_method(D_METHOD("randi_range", "from", "to"), &RandomNumberGenerator::randi_range);
+ ClassDB::bind_method(D_METHOD("rand_weighted", "weights"), &RandomNumberGenerator::rand_weighted);
  ClassDB::bind_method(D_METHOD("randomize"), &RandomNumberGenerator::randomize);
 
  ADD_PROPERTY(PropertyInfo(Variant::INT, "seed"), "set_seed", "get_seed");

core/math/random_number_generator.h

@@ -57,6 +57,8 @@ class RandomNumberGenerator : public RefCounted {
  _FORCE_INLINE_ real_t randfn(real_t p_mean = 0.0, real_t p_deviation = 1.0) { return randbase.randfn(p_mean, p_deviation); }
  _FORCE_INLINE_ int randi_range(int p_from, int p_to) { return randbase.random(p_from, p_to); }
 
+ _FORCE_INLINE_ int rand_weighted(const Vector<float> &p_weights) { return randbase.rand_weighted(p_weights); }
+
  RandomNumberGenerator() { randbase.randomize(); }
 };
 

core/math/random_pcg.cpp

@@ -31,6 +31,7 @@
 #include "random_pcg.h"
 
 #include "core/os/os.h"
+#include "core/templates/vector.h"
 
 RandomPCG::RandomPCG(uint64_t p_seed, uint64_t p_inc) :
  pcg(),
@@ -42,6 +43,26 @@ void RandomPCG::randomize() {
  seed(((uint64_t)OS::get_singleton()->get_unix_time() + OS::get_singleton()->get_ticks_usec()) * pcg.state + PCG_DEFAULT_INC_64);
 }
 
+int RandomPCG::rand_weighted(const Vector<float> &p_weights) {
+ ERR_FAIL_COND_V_MSG(p_weights.is_empty(), -1, "Weights array is empty.");
+ int64_t weights_size = p_weights.size();
+ const float *weights = p_weights.ptr();
+ float weights_sum = 0.0;
+ for (int64_t i = 0; i < weights_size; ++i) {
+ weights_sum += weights[i];
+ }
+
+ float remaining_distance = Math::randf() * weights_sum;
+ for (int64_t i = 0; i < weights_size; ++i) {
+ remaining_distance -= weights[i];
+ if (remaining_distance < 0) {
+ return i;
+ }
+ }
+
+ return -1;
+}
+
 double RandomPCG::random(double p_from, double p_to) {
  return randd() * (p_to - p_from) + p_from;
 }

core/math/random_pcg.h

@@ -59,6 +59,9 @@ static int __bsr_clz32(uint32_t x) {
 #define LDEXPF(s, e) ldexp(s, e)
 #endif
 
+template <class T>
+class Vector;
+
 class RandomPCG {
  pcg32_random_t pcg;
  uint64_t current_seed = 0; // The seed the current generator state started from.
@@ -87,6 +90,8 @@ class RandomPCG {
  return pcg32_boundedrand_r(&pcg, bounds);
  }
 
+ int rand_weighted(const Vector<float> &p_weights);
+
  // Obtaining floating point numbers in [0, 1] range with "good enough" uniformity.
  // These functions sample the output of rand() as the fraction part of an infinite binary number,
  // with some tricks applied to reduce ops and branching:

doc/classes/RandomNumberGenerator.xml

@@ -17,6 +17,25 @@
  <link title="Random number generation">$DOCS_URL/tutorials/math/random_number_generation.html</link>
  </tutorials>
  <methods>
+ <method name="rand_weighted">
+ <return type="int" />
+ <param index="0" name="weights" type="PackedFloat32Array" />
+ <description>
+ Returns a random index with non-uniform weights. Prints an error and returns [code]-1[/code] if the array is empty.
+ [codeblocks]
+ [gdscript]
+ var rnd = RandomNumberGenerator.new()
+
+ var my_array = ["one", "two", "three, "four"]
+ var weights = PackedFloat32Array([0.5, 1, 1, 2])
+
+ # Prints one of the four elements in `my_array`.
+ # It is more likely to print "four", and less likely to print "two".
+ print(my_array[rng.rand_weighted(weights)])
+ [/gdscript]
+ [/codeblocks]
+ </description>
+ </method>
  <method name="randf">
  <return type="float" />
  <description>