Simulation.h

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#pragma once
 
#include "common/Result.h"
#include "graphics/hair/StrandsDatas.h"
 
#include <cstddef>
#include <cstdint>
#include <vector>
 
#include <glm/vec3.hpp>
 
namespace eve::graphics::hair {
 
struct GuideSimParams {
    glm::vec3 gravity{0.f, -9.81f, 0.f};
    float damping = 0.95f;
    int iterations = 4;
    float compliance = 0.f;
    float maxDt = 1.f / 30.f;
    glm::vec3 wind{0.f, 0.f, 0.f};
    float collisionY = -1.0e6f;
};
 
class EVENGINE_API_BACKENDS GuideSimulator {
public:
    GuideSimulator() = default;
 
    [[nodiscard]] Result<void> reset(const StrandsDatas &guides,
                                     const GuideSimParams &params = {});
 
    void clear();
 
    void setParams(const GuideSimParams &params);
    [[nodiscard]] const GuideSimParams &params() const { return params_; }
 
    [[nodiscard]] bool isReady() const { return !curves_.empty(); }
    [[nodiscard]] size_t particleCount() const { return pos_.size(); }
    [[nodiscard]] size_t curveCount() const { return curves_.size(); }
 
    [[nodiscard]] Result<void> setPinnedRoots(const float *rootPositionsXYZ, int rootCount);
 
    [[nodiscard]] Result<void> step(float dt);
 
    [[nodiscard]] Result<StrandsDatas> snapshot() const;
 
private:
    struct CurveSpan {
        uint32_t pointOffset = 0;
        uint32_t pointCount = 0;
        float length = 0.f;
    };
 
    struct Segment {
        uint32_t i0 = 0;
        uint32_t i1 = 0;
        float restLength = 0.f;
    };
 
    void solveDistances(float dt);
    void resolveCollisions();
 
    GuideSimParams params_{};
    std::vector<StrandPoint> restPoints_;
    std::vector<CurveSpan> curves_;
    std::vector<Segment> segments_;
    std::vector<glm::vec3> pos_;
    std::vector<glm::vec3> prev_;
    std::vector<uint8_t> pinned_;  // 1 = immovable
};
 
}  // namespace eve::graphics::hair