time_alpha.h

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#pragma once
 
 
#include "fl/math/math.h"
#include "fl/stl/int.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
 
// Phase of the TimeRamp transition
enum class RampPhase {
    Inactive,  // Not started or finished
    Rising,    // Ramping up from 0 to 255
    Plateau,   // Holding at 255
    Falling    // Ramping down from 255 to 0
};
 
// Use this function to compute the alpha value based on the time elapsed
// 0 -> 255
u8 time_alpha8(u32 now, u32 start, u32 end) FL_NOEXCEPT;
// 0 -> 65535
u16 time_alpha16(u32 now, u32 start, u32 end) FL_NOEXCEPT;
 
inline float time_alphaf(u32 now, u32 start, u32 end) FL_NOEXCEPT {
    if (now < start) {
        return 0.0f;
    }
    u32 elapsed = now - start;
    u32 total = end - start;
    float out = static_cast<float>(elapsed) / static_cast<float>(total);
    return out;
}
 
class TimeAlpha {
  public:
    virtual ~TimeAlpha() FL_NOEXCEPT = default;
    virtual void trigger(u32 now) FL_NOEXCEPT = 0;
    virtual u8 update8(u32 now) FL_NOEXCEPT = 0;
    virtual u16 update16(u32 now) FL_NOEXCEPT {
        return static_cast<u16>(update8(now) << 8) + 0xFF;
    }
    virtual float updatef(u32 now) FL_NOEXCEPT {
        return static_cast<float>(update16(now)) / 65535.0f;
    }
    virtual bool isActive(u32 now) const FL_NOEXCEPT = 0;
};
 
/*
 *                       amplitude
 *                          ^
 *  255 ───────────────────────
 *                     /        \
 *                    /          \
 *                   /            \
 *                  /              \
 *    0 ────────────┴               ┴──────────────────> time (ms)
 *                  t0   t1     t2   t4
 *
 *
 *
 */
class TimeRamp : public TimeAlpha {
  public:
    TimeRamp(u32 risingTime, u32 latchMs, u32 fallingTime) FL_NOEXCEPT;

    void trigger(u32 now) FL_NOEXCEPT override;

    bool isActive(u32 now) const FL_NOEXCEPT override;

    RampPhase getCurrentPhase(u32 now) const FL_NOEXCEPT;

    u8 update8(u32 now) FL_NOEXCEPT override;
 
  private:
    u32 mLatchMs;
    u32 mRisingTime;
    u32 mFallingTime;
 
    u32 mFinishedRisingTime = 0;
    u32 mFinishedPlateauTime = 0;
    u32 mFinishedFallingTime = 0;
 
    u32 mStart = 0;
    u8 mLastValue = 0;
};
 
/*
 *                       amplitude
 *                          ^
 *  255 ──────────────────────────────────────
 *                     /
 *                    /
 *                   /
 *                  /
 *    0 ────────────┴                       --> time (ms)
 *                  t0   t1
 *
 *
 *
 */
class TimeClampedTransition : public TimeAlpha {
  public:
    TimeClampedTransition(u32 duration) FL_NOEXCEPT : mDuration(duration) {}
 
    void trigger(u32 now) FL_NOEXCEPT override {
        mStart = now;
        mEnd = now + mDuration;
    }
 
    bool isActive(u32 now) const FL_NOEXCEPT override {
        bool not_started = (mEnd == 0) && (mStart == 0);
        if (not_started) {
            // if we have not started, we are not active
            return false;
        }
        if (now < mStart) {
            // if the time is before the start, we are not active
            return false;
        }
        if (now > mEnd) {
            // if the time is after the finished rising, we are not active
            return false;
        }
        return true;
    }
 
    u8 update8(u32 now) FL_NOEXCEPT override {
        bool not_started = (mEnd == 0) && (mStart == 0);
        if (not_started) {
            // if we have not started, we are not active
            return 0;
        }
        u8 out = time_alpha8(now, mStart, mEnd);
        return out;
    }
 
    float updatef(u32 now) FL_NOEXCEPT override {
        bool not_started = (mEnd == 0) && (mStart == 0);
        if (not_started) {
            return 0;
        }
        float out = time_alphaf(now, mStart, mEnd);
        if (mMaxClamp > 0.f) {
            out = fl::min(out, mMaxClamp);
        }
        return out;
    }
 
    void set_max_clamp(float max) FL_NOEXCEPT { mMaxClamp = max; }
 
  private:
    u32 mStart = 0;
    u32 mDuration = 0;
    u32 mEnd = 0;
    float mMaxClamp = -1.f; // default disabled.
};
 
} // namespace fl