FPS Shooter

A playbook for first-person shooters — the look/move controller, the shooting model, weapon feel, and combat. This is a compositional skill: it wires a 3D controller, input, and AI into a shooter. It does not re-teach 3D nodes or raycasts; it defines the shooting model and the feel knobs (TTK, recoil, spread) that decide whether the guns feel good.

When to use

• Use when building a first-person game whose core verb is aim and shoot — arena shooter, tactical FPS, PvE shooter, boomer-shooter.
• Use when deciding hitscan vs. projectile, tuning time-to-kill, recoil, spread, or aim feel.

When not to use: third-person/2D shooting → reuse the shooting model here but build the camera/controller from the relevant genre. Wave survival with towers → tower-defense. For the camera/character body itself, use godot-3d-essentials / unreal-cpp-gameplay.

Core loop

Scan → acquire a target → aim and fire → confirm the kill (feedback) → reposition / reload / advance. The whole experience rests on the aim-and-fire micro-loop feeling crisp: responsive look, clear hit feedback, and a death that reads instantly.

Must-have systems

1. First-person controller — move (WASD/stick) + mouse/stick look, gravity, jump/crouch.
2. Camera — eye-height view, configurable FOV and sensitivity, recoil kick.
3. Shooting model — hitscan raycast and/or projectile spawn; one impact path for feedback.
4. Weapons + ammo — damage, fire rate, magazine, reload, switching.
5. Health + damage — HP, hit/headshot multipliers, death; player and enemy share the model.
6. Enemy AI — perceive → alert → attack → search; cover and reaction delays (game-ai).
7. Feedback — hitmarkers, impact decals/particles, hit sounds, screen shake, kill confirms.
8. Objectives — what you do besides shoot: clear, capture, survive, escort.

Design knobs

Knob	Effect	Sane default
Time-to-kill (TTK)	lethality, forgiveness	Tune dmg × fire-rate × HP together (refs).
Hitscan vs projectile	aim skill type	Hitscan = flick; projectile = lead/dodge.
Damage falloff	range limiting	Full to ~20 m, floor by ~60 m.
Headshot multiplier	skill reward	~1.5–2.0×.
Recoil pattern	learnable kick	Fixed pattern > pure random.
Spread (bloom)	suppress laser-accuracy	First shot accurate; grows while firing.
Fire rate / magazine / reload	rhythm, downtime	Reload = vulnerability window.
Mouse sensitivity / FOV	comfort, readability	Always expose both as options.
Aim assist (pad)	controller parity	Magnetism/slowdown near targets.

Patterns

1. Hitscan shot (instant ray, the workhorse)

# Pseudocode. Cast from the camera; first hit takes damage scaled by range + headshot.
direction = apply_spread(camera.forward, current_spread)   # cone sample, see refs §4
hit = raycast(camera.world_position, direction, max_dist=RANGE, mask=SHOOTABLE, exclude=[shooter])
if hit:
    dmg = base_damage * falloff(hit.distance)
    if hit.is_head: dmg *= HEADSHOT_MULT
    hit.actor.take_damage(dmg)
    spawn_impact_fx(hit.point, hit.normal)        # decal + sound + hitmarker

2. Projectile shot (dodgeable, leads the target)

# Pseudocode. Spawn a moving body; it deals damage on its own collision.
p = spawn(projectile_scene, at=muzzle.world_position)
p.velocity = camera.forward * PROJECTILE_SPEED
p.on_hit   = lambda other, point: (other.take_damage(base_damage), explode_fx(point))
p.lifetime = RANGE / PROJECTILE_SPEED             # despawn so shots don't live forever

3. Time-to-kill (balance the trio together)

# Pseudocode. TTK falls out of HP, per-shot damage, and fire rate — tune as one system.
shots_to_kill = ceil(target_hp / damage_per_shot)
ttk_seconds   = (shots_to_kill - 1) / fire_rate_per_second   # first shot at t=0

Pitfalls / failure modes

• Look tied to frame rate or unscaled by dt → sensitivity changes with FPS. Look should be driven by raw mouse delta (never multiplied by dt); movement integration uses dt (see physics-tuning). Clamp pitch to about ±89° so the view cannot flip over.
• Shots that "do nothing" → the ray hits the shooter's own collider, misses hitboxes built from trigger/area volumes, or stops on an invisible trigger zone. Exclude the shooter and set the trigger rule explicitly per engine (refs §2 table).
• Recoil recovery fights the player's aim → recoil was written into the look angle. Keep it as a separate offset that decays to zero (refs §4).
• Pure random recoil/spread → feels uncontrollable and unfair. Use a learnable recoil pattern; keep the first shot accurate.
• Hitscan with no falloff → pistols snipe across the map. Add range-based damage falloff.
• No hit feedback → players can't tell if shots land. Always show hitmarkers, impact FX, and a distinct kill confirm.
• Mismatched TTK → too low feels twitchy/unfair; too high feels spongy. Tune damage, fire rate, and HP as one system (Pattern 3).
• Trusting the client in multiplayer → cheating and "I shot first" disputes. Keep authority server-side; use lag compensation (refs) and defer netcode to the engine multiplayer skill.
• No FOV / sensitivity options → motion sickness and accessibility failures. Always expose them.

Composition (build it from these skills)

• Controller + camera: godot-3d-essentials (Godot) or unreal-cpp-gameplay / unreal-blueprints; Unity uses unity-physics + a character controller.
• Input: input-systems (or unreal-enhanced-input) for look/move, rebinding, and gamepad aim assist.
• Shooting physics: godot-physics / unity-physics for raycasts and projectile collision.
• Enemies: game-ai with unity-navmesh / unreal-behavior-trees / Godot navigation.
• Camera & feel: camera-systems for FOV/recoil kick and look smoothing; game-feel for hit-stop, screen shake, and impact juice.
• Polish: audio-design for weapon/impact sound; shader-programming for muzzle/impact VFX.
• Process: prototype-fast to validate aim feel before building content.

References

• For hitscan vs. projectile trade-offs, damage falloff, recoil/spread, TTK math, hit registration/lag compensation, and enemy AI states, read references/shooting-and-feel.md.