Class alpha16

src/fl/math/alpha.h:87–134

Unsigned 16-bit alpha / brightness — UNORM16. Represents values in [0.0, 1.0] inclusive. Interpretation: raw / 65535 raw 0 = 0.0 raw 32768 = 32768/65535 ~ 0.500 raw 65535 = 65535/65535 = 1.0

///   raw 32768 = 32768/65535 ~ 0.500
///   raw 65535 = 65535/65535 = 1.0
struct alpha16 {
    unsigned short value;

    constexpr alpha16() FL_NOEXCEPT : value(0) {}

    // Accept any non-bool integer type (signed or unsigned, any width).
    template <typename IntT, alpha_detail::enable_if_integer_t<IntT> = 0>
    constexpr alpha16(IntT v) FL_NOEXCEPT : value(static_cast<unsigned short>(v)) {}  // NOLINT — implicit by design

    explicit constexpr alpha16(float f) FL_NOEXCEPT : value(_clamp(f)) {}
    explicit constexpr alpha16(double f) FL_NOEXCEPT : value(_clamp(static_cast<float>(f))) {}
    constexpr operator unsigned short() const FL_NOEXCEPT { return value; }

    constexpr unsigned short raw() const FL_NOEXCEPT { return value; }
    constexpr float to_float() const FL_NOEXCEPT { return value / 65535.0f; }

    static constexpr alpha16 from_float(float f) FL_NOEXCEPT {
        return alpha16(static_cast<unsigned short>(_clamp(f)));
    }

    alpha16& operator+=(unsigned short rhs) FL_NOEXCEPT { value += rhs; return *this; }
    alpha16& operator-=(unsigned short rhs) FL_NOEXCEPT { value -= rhs; return *this; }
    alpha16& operator*=(unsigned short rhs) FL_NOEXCEPT { value *= rhs; return *this; }
    alpha16& operator/=(unsigned short rhs) FL_NOEXCEPT { value /= rhs; return *this; }
    alpha16& operator>>=(int rhs) FL_NOEXCEPT { value >>= rhs; return *this; }
    alpha16& operator<<=(int rhs) FL_NOEXCEPT { value <<= rhs; return *this; }
    alpha16& operator++() FL_NOEXCEPT { ++value; return *this; }
    alpha16 operator++(int) FL_NOEXCEPT { alpha16 t = *this; ++value; return t; }
    alpha16& operator--() FL_NOEXCEPT { --value; return *this; }
    alpha16 operator--(int) FL_NOEXCEPT { alpha16 t = *this; --value; return t; }

    /// Scale a signed integer by this alpha (UNORM16 semantics).
    /// result = (v * (raw + 1)) >> 16
    /// Identity: scale_signed(x) == x when raw == 65535
    /// Zero:     scale_signed(x) == 0 when raw == 0 and |x| < 65536
    template <typename T>
    constexpr T scale_signed(T v) const FL_NOEXCEPT {
        return static_cast<T>(
            (static_cast<long long>(v) *
             static_cast<long long>(static_cast<unsigned int>(value) + 1u)) >> 16);
    }

  private:
    static constexpr unsigned short _clamp(float f) FL_NOEXCEPT {
        return static_cast<unsigned short>(
            f <= 0.0f ? 0 : (f >= 1.0f ? 65535 : static_cast<unsigned short>(f * 65535.0f + 0.5f)));
    }
};

} // namespace fl