Browser FPS games: how they work, and one built for this site

Why a first-person shooter can live in a browser tab

A modern browser ships a complete 3D engine. WebGL 2 talks to the graphics card, Web Audio synthesises sound, pointer lock turns the mouse into a free-look camera, and WebSockets carry a steady stream of small packets to a server. Put together, that is everything a shooter from the early 2000s needed, and the download is a fraction of one of their maps. Krunker.io made the genre popular on the web with short rounds, a stylised look that renders fast on school laptops, and classes you pick in seconds; the same recipe sits under Shell Shockers, Venge and the rest of the io shooters.

The hard part is not the graphics. It is the twenty to two hundred milliseconds between your click and the server, and between the server and everyone else. A browser shooter that feels good has solved three problems: your own movement must respond instantly, other players must move smoothly, and a shot must count where you saw the target, not where the server thinks they are a tenth of a second later.

What good netcode does

• Client-side prediction: your machine moves your body the moment you press a key, with the same rules the server uses, and the server's answer only corrects it when they disagree.
• Interpolation: everyone else is drawn about a hundred milliseconds in the past, between two server snapshots, so they glide instead of teleporting between updates.
• Lag compensation: the server keeps a second of movement history and rewinds the other players to the moment you fired, so a hit on your screen is a hit.
• An authoritative server: damage, fire rate, ammo and movement are decided by the server, so a modified client cannot shoot faster or walk through walls.
• Compact packets: binary snapshots of a few hundred bytes twenty times a second instead of text, with only what changed since the last packet you acknowledged.

Boltline, the arena shooter built for TabSpawn

Boltline is this site's shooter, written from scratch for the browser: a fast arena FPS in the spirit of Krunker, with none of its maps, art or code. Six classes trade health for speed and carry a primary weapon and a gadget: the Vanguard's rifle and frags, the Runner's SMG and smoke, the Bulwark's shotgun and a deployable barrier, the Wraith's sniper, the Marksman's DMR and the Sapper's grenade launcher. Movement rewards practice: sprint into a slide, jump out of it and slide again on landing to carry the speed across a map.

Five arenas each have their own light, from a desert outpost at noon to rain-wet rooftops at dusk and a snowbound station under the aurora, and three modes rotate through them: free for all, team deathmatch and king of the hill. Rooms hold up to ten; quick play finds the best one, a private room gives you a code and a link for friends, and bots fill the gaps so there is always a match. Everything above about netcode is in it: the server simulates sixty times a second, sends binary snapshots at twenty, predicts your body on your machine and rewinds the world for your shots. It also runs entirely offline against bots in practice mode.

Tips for any browser shooter

• Lower the quality preset before blaming your aim. A steady 60 frames a second matters more than shadows.
• Aim down sights for distance, hip-fire up close, and learn where each weapon's recoil goes.
• Keep moving between fights, not during them: strafing while you shoot widens your spread in most games, including this one.
• Watch the ping. Under 80 ms is comfortable; above 150 ms, pick servers or times of day when it drops.
• Play the objective. In king of the hill a barrier or a grenade on the hill edge is worth more than a long kill streak.

More multiplayer on TabSpawn

Jetbrawl is a 2D jetpack deathmatch with the same room-and-bots setup, Airlock is a 3D social deduction game for four to ten, and Dusk Duel 2 is a two-player fighting game on one keyboard. All of them are free, need no account and open in a tab.

Questions