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On every connection, what a player sees is a fraction of a second old. If the server only checked where everyone is now, a perfectly aimed shot could miss because the target has moved on since. Summer keeps a short history of where every character was. When a player fires, the server checks the shot against the moment the player saw, so if it was on target on their screen, it counts. This works for 3D games.

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Games like this

Counter-Strike, Valorant

Instant shots that hit exactly where you aimed.

Overwatch

Projectiles, beams and area abilities, all checked fairly.

For Honor

Melee swings that connect when they look like they connect.

Deep Rock Galactic

Co-op shooting, where every hit lands where you aimed.

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What your players get

On the shooter's screen the target is in the crosshair. By the time the shot reaches the server, the target has moved on. The server checks the shot against where the target was on the shooter's screen, and counts the hit. On the shooter's screen the target is in the crosshair. By the time the shot reaches the server, the target has moved on. The server checks the shot against where the target was on the shooter's screen, and counts the hit.
  • Hits match the screen. A shot that was on target when the player fired counts, even though the target kept moving while the shot travelled to the server.
  • Walls still block. The server checks the walls too, so nobody gets shot through solid cover.
  • No faked hits. The attacking player’s game sends only what they did, such as the aim and the weapon. The server works out who was hit, so a modified client can’t claim hits it didn’t make.

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Pick your setup

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Instant shots

The shot travels in a straight line the moment the player fires, like a rifle or a laser. Summer checks the line against every other character’s hit shape and the walls, at the moment the shooter saw. Your server decides what a hit does: damage, a kill, a hit marker for the shooter. Two shots. One has a clear line to the target and hits. The other is stopped by a wall in front of the target. Two shots. One has a clear line to the target and hits. The other is stopped by a wall in front of the target.

Add fair instant shots. Shots are checked against what the shooter saw; walls block them.

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Abilities, swings and projectiles

Not every attack is a straight line. A shotgun spreads in a cone, a sword sweeps an arc, a fireball travels along a path, and a ground slam hits an area. Your game decides the shape, its range and who it can hurt. Summer gives your server the exact moment the player saw, with every character where it was on their screen, so you test your shape against that. Four attack shapes checked the same way: a straight shot, a cone, a melee arc and a projectile path. Four attack shapes checked the same way: a straight shot, a cone, a melee arc and a projectile path.

Add fair abilities and melee. Cones, swings and projectiles checked against what the player saw.

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How far back the server looks

Your game chooses how old a player’s view may be and still count. Summer recommends a quarter of a second, which covers players with round trips up to about 170 ms. A player whose view is older than that has their shot refused instead of counted.

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Not sure which fits?

Plan hit detection for my game. Your agent reads your weapons and abilities and proposes how each is checked. No code.

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Testing it on your machine

Local Play runs your server and several game windows on one computer, and it can add delay, jitter and packet loss to every window. Shoot at a moving player with a delay of around 100 ms: the hit should count when your crosshair was on them. See Make your game multiplayer.
Does this not help you? Reach out on Discord!