ttt2-remoteplay.rs

//! this program exists only to launch RPCS3, pointed to the Tekken Tag
//! Tournament 2 ROM on my hard drive, with Steam Remote Play. there are a very
//! weird set of circumstances leading to this:
//!
//! as a prerequisite: modern Steam supports a full userspace gamepad input
//! device stack, called "Steam Input". games launched by steam have the Steam
//! Overlay injected into them, which also handles Steam Input. in effect, Steam
//! Input allows arbitrary gamepads, such as PS4 DualShocks or Nintendo Joycons,
//! or even exotic devices like Hitbox/PS4 Hori Fightpads, to be registered and
//! control mapped on the system, entirely through Steam and without any other
//! operating system support. Steam then effectively translates the USB/BT input
//! protocols of these devices into "ordinary" XInput gamepad input devices,
//! which are the standard gamepad input devices recognized by Windows and all
//! Windows games (cf. Linux with its evdev subsystem.) therefore, if your game
//! is from Steam, you can just plug in a PS4 or JoyCon and immediately play any
//! game such as God of War or Halo as if it was an Xbox controller.
//!
//! an even more recent innovation from Steam Input is the ability to virtualize
//! inputs over the network. using Steam Remote Play, gamepad devices from
//! arbitrary computers are instead routed over the internet using a custom
//! streaming UDP protocol, and virtually "plugged into" the host device. this
//! allows online multiplayer to be supported e.g. on classic fighting games
//! that have no online component, by purely virtualizing the input layer, with
//! no extra support.
//!
//! now taking a step back: the goal is to launch Tekken Tag Tournament 2, using
//! RPCS3 as a PS3 emulator, and launch it under Steam, with Steam Input and
//! Steam Remote Play support, so I can play 4-player Pair Play online with
//! friends. there are a number of issues however, including...
//!
//! most notably, when Steam launches a game, it only passes off Steam Input
//! virtual gamepad devices _to the first window that spawns_. therefore it's
//! critical to make sure the only window that appears due to this application
//! is a fully-spawned, running RPCS3 Emulation Window; therefore no
//! conhost.exe, no RPCS3 UI, and nothing else can appear. this requires
//! --no-gui on RPCS3, at minimum...
//!
//! normally, at this point, it would be enough to just add a non-Steam game to
//! the game list in your UI, and launch the game. this will work and the Steam
//! Input virtual gamepads will be assigned, BUT: arbitrary non-Steam games
//! cannot be played with Steam Remote Play, by default, and are therefore
//! limited only to local coop, without online. fixing this requires another
//! hack...
//!
//! second, this application MUST BE RUN FROM STEAM using another "donor game"
//! for Steam Remote Play; this works by replacing the donor game .exe in
//! Steam's download folder with this dependency-free .exe instead after you
//! compile it, which will launch the emulator directly with the right
//! arguments. the donor game has Steam Remote Play listed as "supported",
//! meaning that when Steam sees foo.exe launch from its game directory, it
//! enables support for Remote Play
//!
//! these two things trick Steam into passing its virtual gamepad devices onto
//! RPCS3 directly with no intervention, which allows Tekken Tag Tournament 2 to
//! work online with Remote Play.
//!
//! XXX FIXMEs:
//!   - harcoded paths?
//!   - steam deck support? this trick also is needed on Linux...
//!   - if RemotePlayWhatever[1] is ever fixed, this will be obsoleted (until
//!     RPW breaks again...)
//!
//! [1] https://github.com/m4dEngi/RemotePlayWhatever

// NOTE: you MUST use the windows subsystem for this app, so it does have a
// conhost.exe process spawned for it. (similarly we have to launch RPCS3.exe
// without a visible conhost.exe as well, see below)
#![cfg(target_os = "windows")]
#![windows_subsystem = "windows"]

use std::process::Command;

fn main() {
    if cfg!(target_os = "windows") {
        use std::os::windows::process::CommandExt;
        const CREATE_NO_WINDOW: u32 = 0x08000000;

        Command::new("cmd")
            .args([
                "/C",
                "C:\\MiscApps\\rpcs3\\rpcs3.exe",
                "--no-gui",
                "E:\\roms\\rpcs3\\BLES01702-[TEKKEN TAG TOURNAMENT 2]\\PS3_GAME\\USRDIR\\EBOOT.BIN",
            ])
            .current_dir("C:\\MiscApps\\rpcs3")
            .creation_flags(CREATE_NO_WINDOW) // IMPORTANT: no conhost.exe
            .status()
            .expect("failed to execute process");
    }
}