ExpressionValue.cpp

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#include "ExpressionValue.hpp"
 
#include <polyfem/utils/Logger.hpp>
#include <polyfem/utils/StringUtils.hpp>
 
#include <units/units.hpp>
 
#include <igl/PI.h>
 
#include <tinyexpr.h>
#include <filesystem>
#include <memory>
#ifdef POLYFEM_WITH_PYTHON
// pybind11 enables a debug-only reference counter when NDEBUG is not defined.
// On MSVC that path can fail with C2480 because it uses a function-local
// thread_local variable. Keep the workaround scoped to pybind11's headers.
#if defined(_MSC_VER) && !defined(NDEBUG) && !defined(PYBIND11_HANDLE_REF_DEBUG)
#define POLYFEM_RESTORE_NDEBUG_AFTER_PYBIND11
#define NDEBUG
#endif
#include <pybind11/embed.h>
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#ifdef POLYFEM_RESTORE_NDEBUG_AFTER_PYBIND11
#undef NDEBUG
#undef POLYFEM_RESTORE_NDEBUG_AFTER_PYBIND11
#endif
#endif
 
#include <iostream>
 
namespace polyfem
{
    using namespace io;
 
    namespace utils
    {
#ifdef POLYFEM_WITH_PYTHON
        namespace py = pybind11;
 
        namespace
        {
            class PythonInterpreter
            {
            public:
                static PythonInterpreter &instance()
                {
                    static PythonInterpreter interpreter;
                    return interpreter;
                }
 
                PythonInterpreter(const PythonInterpreter &) = delete;
                PythonInterpreter &operator=(const PythonInterpreter &) = delete;
 
            private:
                PythonInterpreter()
                {
                    if (!Py_IsInitialized())
                    {
                        // Keep the embedded interpreter alive for the process lifetime.
                        // Python-backed ExpressionValues may be destroyed during static
                        // teardown, and finalizing first makes their py::object cleanup unsafe.
#ifdef POLYFEM_PYTHON_EXECUTABLE
                        PyConfig config;
                        PyConfig_InitPythonConfig(&config);
 
                        wchar_t *program_raw = Py_DecodeLocale(POLYFEM_PYTHON_EXECUTABLE, nullptr);
                        if (program_raw == nullptr)
                        {
                            PyConfig_Clear(&config);
                            log_and_throw_error("Failed to decode Python executable path.");
                        }
 
                        PyStatus status = PyConfig_SetString(&config, &config.program_name, program_raw);
                        PyMem_RawFree(program_raw);
                        if (PyStatus_Exception(status))
                        {
                            PyConfig_Clear(&config);
                            log_and_throw_error("Failed to configure embedded Python program_name.");
                        }
 
                        guard_ = new py::scoped_interpreter(&config);
#else
                        guard_ = new py::scoped_interpreter();
#endif
                    }
                }
 
                ~PythonInterpreter() = default;
 
                py::scoped_interpreter *guard_ = nullptr;
            };
 
            void ensure_python_interpreter()
            {
                try
                {
                    (void)PythonInterpreter::instance();
                }
                catch (const std::exception &e)
                {
                    log_and_throw_error(fmt::format("Failed to initialize embedded Python: {}", e.what()));
                }
            }
 
            std::shared_ptr<py::object> make_python_object_holder(py::object value)
            {
                return std::shared_ptr<py::object>(
                    new py::object(std::move(value)),
                    [](py::object *object) {
                        if (Py_IsInitialized())
                        {
                            py::gil_scoped_acquire gil;
                            delete object;
                        }
                        else
                        {
                            (void)object->release();
                            delete object;
                        }
                    });
            }
 
            py::object load_python_value_function(const std::string &path, const std::string &function_name)
            {
                ensure_python_interpreter();
                py::gil_scoped_acquire gil;
 
                py::module_ importlib_util = py::module_::import("importlib.util");
                py::module_ pathlib = py::module_::import("pathlib");
 
                py::object resolved_path = pathlib.attr("Path")(path).attr("resolve")();
                std::string module_name = resolved_path.attr("stem").cast<std::string>();
                std::string resolved_path_str = py::str(resolved_path).cast<std::string>();
 
                py::object spec = importlib_util.attr("spec_from_file_location")(module_name, resolved_path_str);
                if (spec.is_none())
                    log_and_throw_error(fmt::format("Unable to create Python module spec from '{}'", resolved_path_str));
 
                py::object loader = spec.attr("loader");
                if (loader.is_none())
                    log_and_throw_error(fmt::format("Python module '{}' has no loader", resolved_path_str));
 
                py::object module = importlib_util.attr("module_from_spec")(spec);
                loader.attr("exec_module")(module);
 
                if (!py::hasattr(module, function_name.c_str()))
                    log_and_throw_error(fmt::format("Python expression file '{}' must define a function named '{}'", resolved_path_str, function_name));
 
                py::object value = module.attr(function_name.c_str());
                if (!PyCallable_Check(value.ptr()))
                    log_and_throw_error(fmt::format("Python attribute '{}' in '{}' is not callable", function_name, resolved_path_str));
 
                return value;
            }
        } // namespace
 
        void ExpressionValue::init_python(const std::string &path, const std::string &function_name)
        {
            clear();
 
            py::object value = load_python_value_function(path, function_name);
            auto callable = make_python_object_holder(std::move(value));
 
            sfunc_ = [callable](double x, double y, double z, double t, int index) -> double {
                py::gil_scoped_acquire gil;
                py::object out = (*callable)(x, y, z, t, index);
 
                try
                {
                    return out.cast<double>();
                }
                catch (const py::cast_error &)
                {
                    log_and_throw_error("Python expression must return a scalar convertible to double");
                    return 0;
                }
            };
        }
 
#endif
 
        static double min(double a, double b) { return a < b ? a : b; }
        static double max(double a, double b) { return a > b ? a : b; }
        static double smoothstep(double a)
        {
            if (a < 0)
                return 0;
            else if (a > 1)
                return 1;
            else
                return (3 * pow(a, 2)) - (2 * pow(a, 3));
        }
        static double half_smoothstep(double a)
        {
            double b = (a + 1.) / 2.;
            return 2. * smoothstep(b) - 1.;
        }
        static double deg2rad(double d) { return d * igl::PI / 180.0; }
        static double rotate_2D_x(double x, double y, double theta)
        {
            return x * cos(theta) - y * sin(theta);
        }
        static double rotate_2D_y(double x, double y, double theta)
        {
            return x * sin(theta) + y * cos(theta);
        }
        static double smooth_abs(double x, double k)
        {
            return tanh(k * x) * x;
        }
        static double iflargerthanzerothenelse(double check, double ttrue, double ffalse)
        {
            return check >= 0 ? ttrue : ffalse;
        }
        static double sign(double x)
        {
            return (0 < x) - (x < 0);
        }
        static double compare(double a, double b)
        {
            return a < b ? 1.0 : 0.0;
        }
 
        ExpressionValue::ExpressionValue()
        {
            clear();
        }
 
        void ExpressionValue::clear()
        {
            expr_ = "";
            mat_.resize(0, 0);
            mat_expr_ = {};
            sfunc_ = nullptr;
            tfunc_ = nullptr;
            value_ = 0;
            index_ = -1;
        }
 
        void ExpressionValue::init(const double val)
        {
            clear();
 
            value_ = val;
        }
 
        void ExpressionValue::init(const Eigen::MatrixXd &val)
        {
            clear();
 
            mat_ = val;
        }
 
        void ExpressionValue::init(const std::string &expr, const io::ResourceIO &resources)
        {
            clear();
 
            if (expr.empty())
            {
                return;
            }
 
            try
            {
                if (resources.exists(expr) && !resources.is_group(expr))
                {
                    mat_ = resources.read_matrix(expr);
                    return;
                }
            }
            catch (const std::exception &)
            {
            }
 
            expr_ = expr;
 
            double x = 0, y = 0, z = 0, t = 0;
 
            std::vector<te_variable> vars = {
                {"x", &x, TE_VARIABLE},
                {"y", &y, TE_VARIABLE},
                {"z", &z, TE_VARIABLE},
                {"t", &t, TE_VARIABLE},
                {"min", (const void *)min, TE_FUNCTION2},
                {"max", (const void *)max, TE_FUNCTION2},
                {"smoothstep", (const void *)smoothstep, TE_FUNCTION1},
                {"half_smoothstep", (const void *)half_smoothstep, TE_FUNCTION1},
                {"deg2rad", (const void *)deg2rad, TE_FUNCTION1},
                {"rotate_2D_x", (const void *)rotate_2D_x, TE_FUNCTION3},
                {"rotate_2D_y", (const void *)rotate_2D_y, TE_FUNCTION3},
                {"if", (const void *)iflargerthanzerothenelse, TE_FUNCTION3},
                {"compare", (const void *)compare, TE_FUNCTION2},
                {"smooth_abs", (const void *)smooth_abs, TE_FUNCTION2},
                {"sign", (const void *)sign, TE_FUNCTION1},
            };
 
            int err;
            te_expr *tmp = te_compile(expr.c_str(), vars.data(), vars.size(), &err);
            if (!tmp)
            {
                logger().error("Unable to parse: {}", expr);
                logger().error("Error near character {}.", err);
                log_and_throw_error("Invalid expression '{}'.", expr);
            }
            te_free(tmp);
        }
 
        void ExpressionValue::init(const json &vals, const io::ResourceIO &resources)
        {
            clear();
 
            if (vals.is_number())
            {
                init(vals.get<double>());
            }
            else if (vals.is_boolean())
            {
                init(vals.get<bool>() ? 1. : 0.);
            }
            else if (vals.is_array())
            {
                if (vals.empty() || vals[0].is_number())
                {
                    mat_.resize(vals.size(), 1);
 
                    for (int i = 0; i < mat_.size(); ++i)
                    {
                        if (!vals[i].is_number())
                            log_and_throw_error("Expression arrays must contain either only numbers or only expressions.");
                        mat_(i) = vals[i].get<double>();
                    }
                }
                else
                {
                    mat_expr_ = std::vector<ExpressionValue>(vals.size());
 
                    for (int i = 0; i < vals.size(); ++i)
                    {
                        mat_expr_[i].init(vals[i], resources);
                        if (unit_type_set_)
                        {
                            mat_expr_[i].unit_type_ = unit_type_;
                            mat_expr_[i].unit_type_set_ = true;
                        }
                    }
                }
 
                if (t_index_.size() > 0)
                    if (mat_.size() != t_index_.size() && mat_expr_.size() != t_index_.size())
                        logger().error("Specifying varying dirichlet over time, however 'time_reference' does not match dirichlet boundary conditions.");
            }
            else if (vals.is_object())
            {
                units::precise_unit unit;
                if (vals.contains("unit"))
                {
                    if (!vals["unit"].is_string())
                        log_and_throw_error("Expression object 'unit' must be a string.");
 
                    const std::string unit_str = vals["unit"].get<std::string>();
                    if (!unit_str.empty())
                        unit = units::unit_from_string(unit_str);
                }
 
                if (vals.contains("file_name"))
                {
#ifndef POLYFEM_WITH_PYTHON
                    log_and_throw_error(
                        "Python expression '{}' requested, but PolyFEM was built without Python support. "
                        "Reconfigure with -DPOLYFEM_WITH_PYTHON=ON to enable Python expressions.",
                        vals["file_name"].dump());
#else
                    if (!vals["file_name"].is_string())
                        log_and_throw_error("Python expression 'file_name' must be a string.");
                    if (!vals.contains("function_name") || !vals["function_name"].is_string())
                        log_and_throw_error("Python expression '{}' must include a string 'function_name'.", vals["file_name"].get<std::string>());
 
                    const std::string path = resources.materialize(vals["file_name"].get<std::string>()).string();
                    const std::string function_name = vals["function_name"].get<std::string>();
 
                    init_python(path, function_name);
                    unit_ = unit;
                    return;
#endif
                }
 
                if (!vals.contains("value"))
                    log_and_throw_error("Expression object must contain either 'value' or 'file_name'.");
 
                init(vals["value"], resources);
                unit_ = unit;
            }
            else
            {
                init(vals.get<std::string>(), resources);
            }
        }
 
        void ExpressionValue::init(const std::function<double(double x, double y, double z)> &func)
        {
            clear();
 
            sfunc_ = [func](double x, double y, double z, double t, int index) { return func(x, y, z); };
        }
 
        void ExpressionValue::init(const std::function<double(double x, double y, double z, double t)> &func)
        {
            clear();
            sfunc_ = [func](double x, double y, double z, double t, int index) { return func(x, y, z, t); };
        }
 
        void ExpressionValue::init(const std::function<double(double x, double y, double z, double t, int index)> &func)
        {
            clear();
            sfunc_ = func;
        }
 
        void ExpressionValue::init(const std::function<Eigen::MatrixXd(double x, double y, double z)> &func, const int coo)
        {
            clear();
 
            tfunc_ = [func](double x, double y, double z, double t) { return func(x, y, z); };
            tfunc_coo_ = coo;
        }
 
        void ExpressionValue::init(const std::function<Eigen::MatrixXd(double x, double y, double z, double t)> &func, const int coo)
        {
            clear();
 
            tfunc_ = func;
            tfunc_coo_ = coo;
        }
 
        void ExpressionValue::set_t(const json &t)
        {
            if (t.is_array())
            {
                for (int i = 0; i < t.size(); ++i)
                {
                    t_index_[std::round(t[i].get<double>() * 1000.) / 1000.] = i;
                }
 
                if (mat_.size() != t_index_.size() && mat_expr_.size() != t_index_.size())
                    logger().error("Specifying varying dirichlet over time, however 'time_reference' does not match dirichlet boundary conditions.");
            }
        }
 
        double ExpressionValue::operator()(double x, double y, double z, double t, int index) const
        {
            double result;
            if (expr_.empty())
            {
                if (t_index_.size() > 0)
                {
                    t = std::round(t * 1000.) / 1000.;
                    if (t_index_.count(t) != 0)
                    {
                        if (mat_.size() > 0)
                            return mat_(t_index_.at(t));
                        else if (mat_expr_.size() > 0)
                            return mat_expr_[t_index_.at(t)](x, y, z, t, index);
                    }
                    else
                    {
                        logger().error("Cannot find dirichlet condition for time step {}.", t);
                        return 0;
                    }
                }
 
                if (mat_.size() > 0)
                    result = mat_(index_ >= 0 ? index_ : index);
                else if (sfunc_)
                    result = sfunc_(x, y, z, t, index);
                else if (tfunc_)
                    result = tfunc_(x, y, z, t)(tfunc_coo_);
                else
                    result = value_;
            }
            else
            {
 
                std::vector<te_variable> vars = {
                    {"x", &x, TE_VARIABLE},
                    {"y", &y, TE_VARIABLE},
                    {"z", &z, TE_VARIABLE},
                    {"t", &t, TE_VARIABLE},
                    {"min", (const void *)min, TE_FUNCTION2},
                    {"max", (const void *)max, TE_FUNCTION2},
                    {"smoothstep", (const void *)smoothstep, TE_FUNCTION1},
                    {"half_smoothstep", (const void *)half_smoothstep, TE_FUNCTION1},
                    {"deg2rad", (const void *)deg2rad, TE_FUNCTION1},
                    {"rotate_2D_x", (const void *)rotate_2D_x, TE_FUNCTION3},
                    {"rotate_2D_y", (const void *)rotate_2D_y, TE_FUNCTION3},
                    {"if", (const void *)iflargerthanzerothenelse, TE_FUNCTION3},
                    {"compare", (const void *)compare, TE_FUNCTION2},
                    {"smooth_abs", (const void *)smooth_abs, TE_FUNCTION2},
                    {"sign", (const void *)sign, TE_FUNCTION1},
                };
 
                int err;
                te_expr *tmp = te_compile(expr_.c_str(), vars.data(), vars.size(), &err);
                if (!tmp)
                {
                    logger().error("Unable to parse: {}", expr_);
                    logger().error("Error near character {}.", err);
                    log_and_throw_error("Invalid expression '{}'.", expr_);
                }
                result = te_eval(tmp);
                te_free(tmp);
            }
 
            if (!unit_.base_units().empty())
            {
                if (!unit_.is_convertible(unit_type_))
                    log_and_throw_error(fmt::format("Cannot convert {} to {}", units::to_string(unit_), units::to_string(unit_type_)));
 
                result = units::convert(result, unit_, unit_type_);
            }
 
            return result;
        }
    } // namespace utils
} // namespace polyfem