Function compute_eta_from_input

src/fl/gfx/rgbww.cpp.hpp:198–255

}

inline float compute_eta_from_input(const colorimetric_detail::RgbcctProfile& profile,
                                    float s_r, float s_g, float s_b) FL_NOEXCEPT {
    // Compute the input chromaticity in the *source* color space (#2705) when
    // the warm path carries populated input_xy_* fields. Falling back to the
    // emitter-space projection used previously would bias eta toward the LED
    // gamut, so a neutral source white wouldn't blend symmetrically across
    // warm/cool when the source primaries (e.g. sRGB) differ from the LED
    // primaries — exactly the regression flagged on this PR.
    EtaSourceMatrixCache& cache =
        fl::Singleton<EtaSourceMatrixCache>::instance();
    const fl::DiodeProfile& wp = profile.warm_path;
    const bool key_changed =
        !cache.initialized ||
        !xy_equal(cache.xy_r, wp.input_xy_r) ||
        !xy_equal(cache.xy_g, wp.input_xy_g) ||
        !xy_equal(cache.xy_b, wp.input_xy_b) ||
        !xy_equal(cache.xy_w, wp.input_xy_w);
    if (key_changed) {
        cache.xy_r[0] = wp.input_xy_r[0]; cache.xy_r[1] = wp.input_xy_r[1];
        cache.xy_g[0] = wp.input_xy_g[0]; cache.xy_g[1] = wp.input_xy_g[1];
        cache.xy_b[0] = wp.input_xy_b[0]; cache.xy_b[1] = wp.input_xy_b[1];
        cache.xy_w[0] = wp.input_xy_w[0]; cache.xy_w[1] = wp.input_xy_w[1];
        cache.has_M_src = wp.input_xy_w[1] > 1e-6f &&
                          colorimetric_detail::build_source_matrix(
                              wp.input_xy_r, wp.input_xy_g,
                              wp.input_xy_b, wp.input_xy_w, cache.M_src);
        cache.initialized = true;
    }

    float X = 0.0f, Y = 0.0f, Z = 0.0f;
    if (cache.has_M_src) {
        const float s[3] = { s_r, s_g, s_b };
        float xyz[3];
        colorimetric_detail::matvec3(cache.M_src, s, xyz);
        X = xyz[0]; Y = xyz[1]; Z = xyz[2];
    } else {
        // Legacy emitter-space fallback for profiles without populated source.
        // Three xyY_to_XYZ calls per pixel — degraded but still cheap, and
        // only reached when the user explicitly opts out of source space.
        float P_R[3], P_G[3], P_B[3];
        colorimetric_detail::xyY_to_XYZ(wp.xy_r[0], wp.xy_r[1], wp.lum_r, P_R);
        colorimetric_detail::xyY_to_XYZ(wp.xy_g[0], wp.xy_g[1], wp.lum_g, P_G);
        colorimetric_detail::xyY_to_XYZ(wp.xy_b[0], wp.xy_b[1], wp.lum_b, P_B);
        X = P_R[0]*s_r + P_G[0]*s_g + P_B[0]*s_b;
        Y = P_R[1]*s_r + P_G[1]*s_g + P_B[1]*s_b;
        Z = P_R[2]*s_r + P_G[2]*s_g + P_B[2]*s_b;
    }
    const float sum = X + Y + Z;
    if (sum < 1e-9f) return 0.5f;
    const float input_x = X / sum;
    const float warm_x = profile.warm_path.xy_w[0];
    const float cool_x = profile.cool_path.xy_w[0];
    if (cool_x == warm_x) return 0.5f;
    const float eta = (input_x - warm_x) / (cool_x - warm_x);
    if (eta < 0.0f) return 0.0f;
    if (eta > 1.0f) return 1.0f;
    return eta;
}