Overview

This genre pack targets driving and racing games in the Forza / Gran Turismo / arcade-kart mould: a vehicle defined by drivetrain and chassis attributes, track surfaces and tuning parts that modify performance, signature driver abilities (nitro, drift), and — at its core — a traction pipeline that has to stay coherent as surfaces, upgrades, and physics all push on grip at once.

It is the practical, copy-and-extend companion to the Racing (Forza-style) case study in the core specification (Section 15.2). Where the case study sketches the vehicle attribute set, biome surface effects, and the traction ExecutionCalculation, this pack ships the matching schema-conformant Attributes, Tags, Abilities, and Effects in entities/, plus a worked vehicle in entities/gameplay_controller.yaml.

Relationship to the core specification

This document is additive. It defines genre-specific Attributes, Tags, Abilities, and Effects on top of the core Universal Gameplay Ability System specification.

  • It MUST NOT redefine, override, or contradict any concept in the core spec.

  • All entities in entities/ validate against the same schemas/*.json as the core.

  • It reuses core state tags (State.Alive, State.Combat, …) by reference where relevant — it never re-declares them.

  • The grip stacking it relies on is the core modifier Channel mechanism (core spec §5.3 and §15.2), and the non-linear physics coupling is a core ExecutionCalculation — neither is a new construct.

Genre Attributes

Defined in entities/attribute_set.yaml as the VehiclePerformanceSet set.

Attribute Category Role

EngineTorque

Statistic

Drive torque (Nm); raised by tuning upgrades.

MaxSpeed

Statistic

Top speed (km/h); lowered by low-grip surfaces, raised by boost.

AeroDownforce

Statistic

Downforce coefficient; scales effective traction with speed.

TireGripMultiplier

Statistic

The aggregated grip stat targeted by the traction channels.

TireTemperature

Statistic

Tire core temperature (°C), clamped to [20, 150]; grip peaks in the 80–100 window.

MaxBoost / Boost

Statistic / Resource

Boost is clamped to [0, MaxBoost]; spent by the nitro ability and refilled by drifting.

EngineRPM, CurrentSpeed, AvailableTraction

Meta

Runtime telemetry written each frame by the physics simulation and the traction calc.

The traction pipeline (the core racing mechanic)

Grip in a racing game is pushed on from several directions at once — the surface under the tires, the parts bolted to the car, downforce that grows with speed, and tire temperature. UGAS expresses this in two complementary layers, both landing on TireGripMultiplier / AvailableTraction.

Declarative grip channels

Surface and upgrade modifiers stack through named channels: additive within a channel, multiplicative across channels — exactly the damage-bucket mechanism from §15.3, reused for grip.

Channel What goes in it Stacking

Surface

The current track surface (asphalt, mud, gravel, ice, wet)

Additive within

Upgrades

Tuning parts and tire compounds

Additive within, multiplied across the others

Because channels are part of the core modifier pipeline, surface and tuning effects stack declaratively in Effect YAML — no custom calculation code is needed for them.

Worked example (entities/gameplay_controller.yaml)

A Sport-class car with the sport tuning package fitted, driving on mud:

  • Surface factor (mud, \(-0.6\)): \(1 + (-0.6) = 0.40\)

  • Upgrades factor (tuning, \(+0.10\)): \(1 + 0.10 = 1.10\)

  • Final TireGripMultiplier: \(1.0 \times 0.40 \times 1.10 = 0.44\)

The same two effects add flat drivetrain changes: EngineTorque \(400 + 80 = 480\) and MaxSpeed \(250 + 20 - 30 = 240\). These are exactly the CurrentValue entries recorded for the example vehicle.

Physics coupling via ExecutionCalculation

Downforce scaling (\(\propto \text{speed}^2\)) and the tire-temperature window are non-linear, so they live in an ExecutionCalculation rather than a channel. GE_Traction_Update (entities/effect_traction_update.yaml) invokes ExecCalc_VehicleTraction, which reads the aggregated TireGripMultiplier, AeroDownforce, TireTemperature, and CurrentSpeed and writes AvailableTraction. The simulation re-applies this instant effect each physics step. See §15.2 for the reference calculation body.

Genre Tags

Defined in entities/tag_registry.yaml (additive only):

  • Surfaces — Surface.Asphalt|Mud|Gravel|Ice|Wet.

  • Vehicle classification — the base Vehicle tag (required by surface effects), Vehicle.Class.Sport|Kart|Formula, and Vehicle.Tuned.

  • Vehicle states — Vehicle.State.Boosting|Drifting|SpunOut.

  • Ability types — Ability.Type.Boost|Handling.

  • Race progression — Race.Phase.Countdown|Racing|Finished, Race.Status.FinalLap.

Genre Abilities

  • entities/ability_nitro_boost.yaml — GA_NitroBoost: spends the Boost resource (Cost: GE_NitroCost) on a cooldown (GE_NitroCooldown) and applies GE_NitroBoost to the vehicle. Blocked while Vehicle.State.SpunOut; requires Race.Phase.Racing.

  • entities/ability_drift.yaml — GA_Drift: hold-to-slide handling technique. Grants Vehicle.State.Drifting while active and applies the periodic GE_DriftCharge, trading cornering grip for boost charge. Ends on input release (WaitInputRelease).

Genre Effects

  • entities/effect_tuning_sport.yaml — GE_Tuning_Sport: infinite upgrade; flat +EngineTorque / +MaxSpeed and +10% grip in the Upgrades channel; grants Vehicle.Tuned.

  • entities/effect_biome_mud.yaml — GE_Biome_Mud: infinite surface; -60% grip in the Surface channel and -30 MaxSpeed; grants Surface.Mud. Requires the Vehicle tag.

  • entities/effect_biome_asphalt.yaml — GE_Biome_Asphalt: infinite surface; Override`s the `Surface-channel grip back to the 1.0 baseline; grants Surface.Asphalt.

  • entities/effect_nitro_boost.yaml — GE_NitroBoost: HasDuration burst; flat +EngineTorque / +MaxSpeed; grants Vehicle.State.Boosting.

  • entities/effect_drift_charge.yaml — GE_DriftCharge: HasDuration + Period; restores Boost every half-second; grants Vehicle.State.Drifting.

  • entities/effect_traction_update.yaml — GE_Traction_Update: instant; runs the ExecCalc_VehicleTraction ExecutionCalculation to recompute AvailableTraction.

Using this pack

  1. Copy genres/racing/ into your project (or load entities/ directly via the ugas-schema-author skill).

  2. Keep, rename, or extend the VehiclePerformanceSet; add vehicle classes/parts as new Effects, and driver techniques as new Abilities.

  3. Author new grip modifiers by choosing the right Channel — surface conditions go in Surface, parts and compounds in Upgrades; reserve `ExecutionCalculation`s for non-linear physics coupling.

  4. Validate with python scripts/validate_schema_examples.py before committing.