encoder_acceleration.h

#pragma once
 
#include <algorithm>
#include <cstdint>
 
namespace deluge::hid::encoders {
 
class EncoderAcceleration {
public:
    struct Tuning {
        // - acceleration and inertia (1 - acceleration) control how fast the knob speeds up
        // - speedScale controls how we go from "raw speed" to speed used as offset multiplier
        // - min and max speed clamp the max effective speed
        //
        // current values have been tuned to be slow enough to feel easy to control, but fast
        // enough to go from 0 to 50 with one fast turn of the encoder. speedScale and min/max
        // could potentially be user-configurable in a small range.
        double acceleration = 0.1;
        double speed_scale = 0.15;
        double min_multiplier = 1.0;
        double max_multiplier = 3.0;
        double reset_after = 0.3;
    };
 
    double advance(int8_t offset, double time) { return advance(offset, time, Tuning{}); }
    double advance(int8_t offset, double time, Tuning tuning) {
        const double elapsed = time - last_time_;
        if (elapsed >= tuning.reset_after || elapsed < 0.0 || (offset > 0) != (last_offset_ > 0)) {
            // too much time passed, or the knob direction changed, reset the speed
            speed_ = 0.0;
        }
        else if (elapsed > 0.0) {
            // moving in the same direction, update speed
            speed_ = speed_ * (1.0 - tuning.acceleration) + tuning.acceleration / elapsed;
        }
        // last_time and last_offset keep track of our time and direction. Only the sign of the offset
        // matters: fast rotation mixes single- and multi-tick batches in the same direction.
        last_time_ = time;
        last_offset_ = offset;
        return std::clamp(speed_ * tuning.speed_scale, tuning.min_multiplier, tuning.max_multiplier);
    }
    void reset() { *this = {}; }
 
private:
    double speed_ = 0.0;
    double last_time_ = 0.0;
    int8_t last_offset_ = 0;
};
 
inline constexpr EncoderAcceleration::Tuning kGoldEncoderAcceleration{};
inline constexpr EncoderAcceleration::Tuning kHorizontalMenuAcceleration{.max_multiplier = 5.0};
 
} // namespace deluge::hid::encoders