switched_exciter.hpp

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// sbl/dsp/pm/switched_exciter.hpp — One of two exciters, chosen per block (Physical modeling — composition)
//
// An app that lets a player switch bow models owns two exciters and this:
// the string sees one Exciter and never learns there are two. The choice is
// read at advance(), once a block, so the sample loop has no branch in it;
// the exciter switched to starts from rest.
 
#ifndef SBL_DSP_PM_SWITCHED_EXCITER_HPP_
#define SBL_DSP_PM_SWITCHED_EXCITER_HPP_
 
#include <cstdint>
 
#include <sbl/dsp/diagram/graph.hpp>
#include <sbl/dsp/pm/contracts.hpp>
 
namespace sbl::dsp::pm {
 
template<typename A, typename B>
class SwitchedExciter {
    static_assert(is_exciter_v<A> && is_exciter_v<B>, "both sides are Exciters (physical-modeling.md §4.2)");
 
public:
    /// @note All public methods are ISR-safe — bounded computation, no I/O.
 
    SwitchedExciter(A& a, B& b) : a_(a), b_(b) {}
 
    /// Which one plays: false the first, true the second. Takes effect at the next block.
    void select(bool second) { pending_ = second; }
    bool second() const { return use_b_; }
 
    void advance(uint16_t n) {
        if (pending_ != use_b_) {
            use_b_ = pending_;
            if (use_b_) b_.reset(); else a_.reset();
        }
        if (use_b_) b_.advance(n); else a_.advance(n);
    }
 
    float excite(const JunctionState& j) { return use_b_ ? b_.excite(j) : a_.excite(j); }
    float energy() const { return use_b_ ? b_.energy() : a_.energy(); }
 
    void reset() {
        a_.reset();
        b_.reset();
    }
 
    diagram::Ports describe(diagram::Graph& g, uint8_t group, const char* name = "exciter") const {
        return use_b_ ? b_.describe(g, group, name) : a_.describe(g, group, name);
    }
 
private:
    A& a_;
    B& b_;
    bool use_b_ = false;
    bool pending_ = false;
};
 
} // namespace sbl::dsp::pm
 
#endif // SBL_DSP_PM_SWITCHED_EXCITER_HPP_