feat: expose controller port device API for EmulatorJS

[chrisallenlane]

Body

Hi, all.

Over the weekend I embedded EmulatorJS in a project, and realized that lightgun support was not implemented. This is one of two PRs that implements it. (You can see it working now in the linked project - I've applied these patches there already.)

I am a software engineer, but I am not a C programmer, so please take a close look at this one. That said, the I've robustly tested the changes (meaning: I've beaten Battleclash and Metal Combat: Falcon's Revenge several times today, lol), and I've encountered no issues.

I hope this is helpful. I'm happy to answer any questions.

Summary

This adds two new WASM-exported functions and lightgun input handling to enable EmulatorJS to support controller port device switching at runtime -- most notably, lightgun peripherals like the SNES Super Scope.

Currently, EmulatorJS has no way to change a port's device type (e.g. from Joypad to Super Scope). The core reports available device types via RETRO_ENVIRONMENT_SET_CONTROLLER_INFO, and core_set_controller_port_device() exists internally, but neither is exposed to JavaScript. This means lightgun games are unplayable across all systems.

Changes

runloop.c -- Two new functions inside #ifdef EMULATORJS:

• ejs_get_controller_port_info() -- Serializes the controller info already stored in sys_info->ports (reported by the core via SET_CONTROLLER_INFO) into a parseable port:deviceId:description\n string. Follows the same pattern as get_core_options().

• ejs_set_controller_port_device(port, device) -- Thin wrapper around core_set_controller_port_device().

input/drivers/emulatorjs_input.c -- Added RETRO_DEVICE_LIGHTGUN case to rwebinput_input_state():

• Mouse position mapped to LIGHTGUN_SCREEN_X/Y via existing viewport translation
• Mouse buttons mapped to lightgun buttons:
  • Left click: Trigger
  • Right click: AUX_A (Cursor)
  • Middle click: AUX_B (Turbo)
  • Button 4: Start (Pause)
  • Button 5: Select
• Advertised lightgun capability in rwebinput_get_capabilities()

Makefile.emulatorjs -- Added both new functions to EXPORTED_FUNCTIONS.

Testing

Tested with snes9x core running SNES Super Scope games (Battle Clash, Metal Combat: Falcon's Revenge, Super Scope 6). Crosshair tracks mouse, fire/cursor/turbo buttons work correctly, device type persists across settings changes.

Related issues

• [HELP] how to use Super Scope? M.A.C.K Rifle? on SNE9X Core? EmulatorJS#677 -- "How to use Super Scope on snes9x core?"
• SNES Light Gun / Super Scope support EmulatorJS#272 -- "SNES Light Gun / Super Scope support"
• [enhancement] Mouse Controls? EmulatorJS#816 -- "Mouse Controls?" (maintainer noted "we do also need to pass device ids to retroarch")
• Feature Request: Light gun support for PSX EmulatorJS#1117 -- "Light gun support for PSX"

Companion PR

The EmulatorJS JavaScript UI changes that consume these new exports will be submitted as a separate PR to EmulatorJS/EmulatorJS.

[BinBashBanana]

This looks good to me