How it works

A CAPTCHA that lets you play DOOM® to prove you're human (for educational and entertainment purposes)

The project works by leveraging Emscripten to compile a minimal port of Doom to WebAssembly and enable intercommunication between the C-based game runloop (g_game.c) and the JavaScript-based CAPTCHA UI.

Some extensions were made to the game to introduce relevant events needed for its usage in the context of a CAPTCHA.

• Started out with a minimal, SDL-based port of Doom that can be efficiently compiled to WebAssembly
• Tweaked the build to make it compatible with the shareware version of wad (doom1.wad) for legal use
• Introduced new unofficial process flags:
  • -nomenu (m_menu.c) to skip the main menu and jump straight into the game
  • -autoreborn (p_mobj.c) to automatically rebirth the player after a 2s delay
• Introduced callbacks into JS land to be used by the CAPTCHA UI:
  • onPlayerBorn when the player is born or reborn
  • onPlayerKilled when the player is killed
  • onEnemyKilled when the main player kills an enemy
• Tweaked the default process flags in d_main.c to make the game more challenging:
  • -skill 5 sets the difficulty to "Nightmare!"
  • -fast makes it even harder
  • -warp e1m1 jumpstarts the game to where the action is
  • -nomenu doesn't let the player trigger the main menu

See the v0 UI generation or get the source.

Built on the shareware version of DOOM® released publically for non-commercial use. DOOM® is a registered trademark of id Software LLC, a ZeniMax Media company.