v1.4.4

source/core/StarRandomPoint.hpp

@@ -0,0 +1,79 @@
+#ifndef STAR_RANDOM_POINT_HPP
+#define STAR_RANDOM_POINT_HPP
+
+#include "StarRandom.hpp"
+#include "StarPoly.hpp"
+#include "StarTtlCache.hpp"
+
+namespace Star {
+
+// An "infinite" generator of points on a 2d plane, generated cell by cell with
+// an upper and lower cell density range.  Each point is generated in a
+// predictable way sector by sector, as long as the generator function is
+// predictable and uses the RandomSource in a predictable way.  Useful for
+// things like starfields, fields of debris, random object placement, etc.
+
+template <typename PointData>
+class Random2dPointGenerator {
+public:
+  typedef List<pair<Vec2F, PointData>> PointSet;
+
+  Random2dPointGenerator(uint64_t seed, float cellSize, Vec2I const& densityRange);
+
+  // Each point will in the area will be generated in a predictable order, and
+  // if the callback uses the RandomSource in a predictable way, will generate
+  // the same field for every call.
+  template <typename PointCallback>
+  PointSet generate(PolyF const& area, PointCallback callback);
+
+private:
+  HashTtlCache<Vec2F, PointSet> m_cache;
+
+  uint64_t m_seed;
+  float m_cellSize;
+  Vec2I m_densityRange;
+};
+
+template <typename PointData>
+inline Random2dPointGenerator<PointData>::Random2dPointGenerator(uint64_t seed, float cellSize, Vec2I const& densityRange)
+  : m_seed(seed), m_cellSize(cellSize), m_densityRange(densityRange) {}
+
+template <typename PointData>
+template <typename PointCallback>
+auto Random2dPointGenerator<PointData>::generate(PolyF const& area, PointCallback callback) -> PointSet {
+  auto bound = area.boundBox();
+  int64_t sectorXMin = std::floor(bound.xMin() / m_cellSize);
+  int64_t sectorYMin = std::floor(bound.yMin() / m_cellSize);
+  int64_t sectorXMax = std::ceil(bound.xMax() / m_cellSize);
+  int64_t sectorYMax = std::ceil(bound.yMax() / m_cellSize);
+
+  PointSet finalResult;
+
+  for (int64_t x = sectorXMin; x <= sectorXMax; ++x) {
+    for (int64_t y = sectorYMin; y <= sectorYMax; ++y) {
+      auto sector = RectF::withSize({x * m_cellSize, y * m_cellSize}, Vec2F::filled(m_cellSize));
+      if (!area.intersects(PolyF(sector)))
+        continue;
+
+      finalResult.appendAll(m_cache.get(Vec2F(x, y), [&](Vec2F const&) {
+          PointSet sectorResult;
+
+          RandomSource sectorRandomness(staticRandomU64(m_seed, x, y));
+
+          unsigned max = sectorRandomness.randInt(m_densityRange[0], m_densityRange[1]);
+          for (unsigned i = 0; i < max; ++i) {
+            Vec2F pointPos = Vec2F(x + sectorRandomness.randf(), y + sectorRandomness.randf()) * m_cellSize;
+            sectorResult.append(pair<Vec2F, PointData>(pointPos, callback(sectorRandomness)));
+          }
+
+          return sectorResult;
+        }));
+    }
+  }
+
+  return finalResult;
+}
+
+}
+
+#endif