Jungfraujoch/image_analysis/structure_refinement/RefinementGPUEngine.h

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

#pragma once

// The device half of restrained refinement on a GPU (RefinementGPU.h, CUDA builds only). The host half works
// out with gemmi everything that depends on the cell, the group and the reflections; this half grids the atoms,
// transforms, composes the symmetry, evaluates the likelihood target, takes its derivative back to every atom
// by the FFT method, and evaluates the geometry restraints. Every kernel is deterministic - gathers and fixed
// reduction trees, no floating-point atomics - so the same input gives the same bits on every run.

#include <array>
#include <cstddef>
#include <memory>
#include <vector>

#include "ModelDensityGPU.h"
#include "ModelMaskGPU.h"
#include "RefinementMath.h"

// Everything an engine needs that does not depend on the atoms.
struct RefinementGPUSetup {
    ModelDensityGrid grid;                     // the structure-factor grid, u fastest
    double volume = 0;
    std::vector<std::array<int, 12>> sym_ops;  // gemmi's Op: rot row-major and tran, in units of 1 / den
    int den = 24;
    double centring = 1;                       // the number of centring vectors
    std::vector<ModelMaskOp> mask_ops;         // every operator with every centring vector
    std::vector<std::array<int, 3>> rows;      // the reflections, in the order their numbers come back
    std::vector<double> inv_d2;
    std::vector<float> fo;
    std::vector<char> work, centric;
    // The adjoint of the composition, as a gather: the half-u spectrum points the gradient's coefficients
    // land on (ascending), and for each the terms (row * ops + op) * 2 + conj adding to it, in order.
    std::vector<int> scatter_point, scatter_start, scatter_term;
    size_t max_atoms = 0, max_pairs = 0;
};

struct RefinementGPUEngineImpl;

class RefinementGPUEngine {
public:
    static size_t DeviceBytes(const RefinementGPUSetup &setup, size_t fft_work_bytes, size_t max_records,
                              size_t max_slots);
    static size_t FFTWorkBytes(int device, const ModelDensityGrid &grid);

    RefinementGPUEngine(int device, const RefinementGPUSetup &setup, size_t fft_work_bytes);
    ~RefinementGPUEngine();

    // n_cen exp(blur s^2 / 4) per reflection: prepare_asu_data()'s unblur.
    void SetBlur(double blur);
    // Per macro-cycle: F_model = k_total (F + fmask), and the likelihood's D and variance.
    void SetRowModel(const std::vector<float> &k_total, const std::vector<std::array<float, 2>> &fmask,
                     const std::vector<float> &d, const std::vector<float> &var);

    // The atoms, as ModelStructureFactorsGPU takes them: densities, grid positions (fractional times the grid
    // size, not wrapped) and the boxes of ModelDensityGPU::Boxes().
    void SetAtoms(const std::vector<ModelDensityAtom> &atoms, const std::vector<std::array<float, 4>> &pos);
    // F of the atoms at the rows.
    void Fcalc(std::vector<std::array<float, 2>> &f);
    // The bulk-solvent mask's F at the rows (the mask atoms fractional, wrapped).
    void Fmask(const std::vector<ModelMaskAtom> &mask_atoms, std::vector<std::array<float, 2>> &f);
    // -ln L over the working rows for the atoms last set and, with `grad`, dT/d(x, y, z, B) per atom.
    double Evaluate(std::vector<std::array<float, 4>> *grad);

    // Restraint set `which` (0 or 1), as RestraintSet holds it.
    void SetRestraints(int which, const std::vector<RestraintRecord> &records, const std::vector<int> &plane_atoms,
                       const std::vector<int> &slot_start, const std::vector<int> &slot_index, int n_slots);
    // The sum of E of set `which` at `xyzb` (x, y, z, B per atom) and dE/d(x, y, z, B) per atom.
    double EvaluateRestraints(int which, const std::vector<std::array<float, 4>> &xyzb,
                              std::vector<std::array<float, 4>> *grad);

    // The most atoms of a plane restraint the kernel takes.
    static constexpr int MAX_PLANE_ATOMS = 32;

private:
    std::unique_ptr<RefinementGPUEngineImpl> impl_;
};