Jungfraujoch/writer/NXmxModules.cpp

// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#include "NXmxModules.h"

#include <cmath>

namespace {

// Internal frame (x = column, y = row downward, z = beam) -> McStas, a half turn about z.
std::vector<double> ToMcStas(const Coord &v) {
    return {0.0 - v.x, 0.0 - v.y, 0.0 + v.z};
}

// A translation of `length` metres along v (pixels, internal frame), as NXmx writes one: the length as
// the value, the direction as a unit vector - and a zero translation with a unit vector all the same.
void SaveTranslation(HDF5Group &group, const std::string &name, const RotMatrix &delta, double dx_px, double dy_px,
                     double pixel_size_m, const std::string &depends_on) {
    const double len_px = std::hypot(dx_px, dy_px);
    const Coord dir = len_px > 0 ? Coord(static_cast<float>(dx_px / len_px), static_cast<float>(dy_px / len_px), 0)
                                 : Coord(0, 0, 1);
    SaveScalar(group, name, len_px * pixel_size_m)->
            Transformation("m", depends_on, "", "", "translation", ToMcStas(delta * dir), {0, 0, 0}, "");
}

}  // namespace

void WriteNXmxModules(HDF5Object &file, const DetectorModules &modules, double pixel_size_m,
                      const DetectorOrientation &orientation, const std::string &depends_on) {
    const RotMatrix delta = orientation.Matrix();
    // A NXmx reader lists the groups by name (dxtbx, through h5py), and its panel n is the n-th of them:
    // the index is zero-padded to the width of the last one (module_00 ... module_15), so that panel n is
    // module n - and the index /entry/MX/peakPanel gives.
    const size_t digits = std::to_string(modules.size() - 1).size();
    for (size_t n = 0; n < modules.size(); n++) {
        const DetectorModule &m = modules[n];
        std::string index = std::to_string(n);
        index.insert(0, digits - index.size(), '0');
        const std::string path = "/entry/instrument/detector/module_" + index;
        HDF5Group group(file, path);
        group.NXClass("NXdetector_module");
        group.SaveVector("data_origin", std::vector<int32_t>{static_cast<int32_t>(m.y0), static_cast<int32_t>(m.x0)});
        group.SaveVector("data_size", std::vector<int32_t>{static_cast<int32_t>(m.height),
                                                           static_cast<int32_t>(m.width)});
        SaveTranslation(group, "module_offset", delta, m.ox, m.oy, pixel_size_m, depends_on);
        SaveTranslation(group, "fast_pixel_direction", delta, m.fx, m.fy, pixel_size_m, path + "/module_offset");
        SaveTranslation(group, "slow_pixel_direction", delta, m.sx, m.sy, pixel_size_m, path + "/module_offset");
        // Not NXmx: which way the module's readout axes run in the stored image (jfjoch_api.yaml
        // detector_module_direction), so that its readout pixel 0 and axes name it in a module placement.
        group.SaveScalar("readout_fast_axis", DirectionName(m.fast));
        group.SaveScalar("readout_slow_axis", DirectionName(m.slow));
    }
}

void WriteModuleGeometryFile(const std::string &path, const DetectorModules &modules,
                             const DiffractionGeometry &geom) {
    HDF5File file(path);
    HDF5Group(file, "/entry").NXClass("NXentry");
    HDF5Group(file, "/entry/instrument").NXClass("NXinstrument");
    HDF5Group(file, "/entry/instrument/detector").NXClass("NXdetector");
    HDF5Group transformations(file, "/entry/instrument/detector/transformations");
    transformations.NXClass("NXtransformations");

    // Sample -> image pixel (0, 0), square to the beam: what the modules' offsets are measured from. The
    // tilt, if any, is the master file's to state; this file carries the modules only.
    const double pixel_m = geom.GetPixelSize_mm() / 1000.0;
    const RotMatrix delta = geom.GetOrientation().Matrix();
    const auto v = ToMcStas(delta * Coord(-geom.GetBeamX_pxl() * static_cast<float>(pixel_m),
                                          -geom.GetBeamY_pxl() * static_cast<float>(pixel_m),
                                          geom.GetDetectorDistance_mm() / 1000.0f));
    const double len = std::sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
    SaveScalar(transformations, "translation", len)->
            Transformation("m", ".", "detector", "detector_arm", "translation",
                           std::vector<double>{v[0] / len, v[1] / len, v[2] / len});
    SaveScalar(file, "/entry/instrument/detector/depends_on",
               std::string("/entry/instrument/detector/transformations/translation"));

    WriteNXmxModules(file, modules, pixel_m, geom.GetOrientation(),
                     "/entry/instrument/detector/transformations/translation");
}