Native C++ scripting

What is this?

The original Joban Client Mod (JCM) lets resource packs write dynamic display scripts in JavaScript. The Yanyang fork adds C++ native scripting on top: scripts are compiled into native shared libraries (.dll / .so / .dylib) which the mod loads in game and drives frame by frame.

C++ and JS scripts can be mixed within the same declaration entry and rendered at the same time. The mod detects the language automatically from file characteristics—.js is JavaScript, everything else is parsed as a C++ module. Each side captures its own draw commands and replays them independently, without interference.

The journey of a frame

A fifteen-line PIDS script

#include <mtr/script.hpp>

struct ArrivalState {};

struct ArrivalDisplay : mtr::PidsScript<ArrivalState> {
    static constexpr auto ID = "example:arrivals";

    void render(mtr::PidsContext& ctx, ArrivalState&, const mtr::Pids& pids) override {
        for (int row = 0; row < pids.rows(); row++) {
            if (pids.is_row_hidden(row)) continue;
            std::string text = pids.get_custom_message(row).str();
            if (text.empty() && row < pids.arrivals().size())
                text = pids.arrivals().at(row).destination().str();
            if (!text.empty())
                mtr::Text::create().text(text.c_str())
                    .pos(2, row * 10.0 + 2).size(pids.width() - 4, 9).draw(ctx);
        }
    }
};

MTR_REGISTER_PIDS_SCRIPT(ArrivalDisplay)

No JNI, no reflection, no per-call boxing—pids.rows() and arrivals().at(i).destination() are plain memory reads on a compact snapshot.

When to choose C++

Compatibility

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