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