Top-Down Racer Demo Spec

Goal

Build a top-down racing demo that exercises continuous movement, acceleration, steering, collision against a track, checkpoints, lap timing, HUD updates, and persistent interactive rendering.

Player Experience

The game opens directly onto a visible race track with a small car at the starting line. The player accelerates, brakes, steers around the track, passes checkpoints in order, completes laps, and sees lap times and best time.

Track

• Use a closed-loop track visible from a top-down camera.
• The track has a drivable road, off-road area, walls or boundaries, start/finish line, and ordered checkpoints.
• Track can be defined with simple rectangles, polygons, or a tile map.
• The full track should be visible without camera scrolling for the base demo.
• Off-road slows the car; hard walls block or bounce the car.

Controls

• Up or W: accelerate.
• Down or S: brake or reverse.
• Left or A: steer left.
• Right or D: steer right.
• Space: handbrake or quick brake.
• P: pause or resume.
• R: reset car to start or restart race after finish.
• Esc: request close when hosted interactively.

Driving Model

• Car has position, velocity, heading, acceleration, drag, and turn rate.
• Steering should depend on movement speed, with reduced turning when nearly stopped.
• Reverse is allowed but slower than forward movement.
• Off-road applies higher drag and lower max speed.
• Wall collision prevents leaving the allowed world and should not trap the car permanently.

Laps and Checkpoints

• A lap counts only after checkpoints are crossed in order.
• Wrong-way crossing should not count progress.
• Default race target is 3 laps.
• Show current lap, checkpoint progress, current lap time, best lap time, and total time.
• Finish state appears after completing the target laps.

Scoring

No points are required. Success is measured by lap completion and time. Optional medals may be shown based on total time, but they are not required.

Visual Requirements

• Render road, grass/off-road, walls/barriers, start line, checkpoint markers, car, and HUD.
• Car heading must be visually obvious.
• Checkpoints should be visible but not obscure the road.
• HUD should not cover the track in a way that prevents evidence inspection.
• Track layout must resize cleanly while preserving proportions.

Game State

Track at minimum:

• Car position, velocity, heading, throttle/brake/steer inputs, surface type, and reset state.
• Track geometry, checkpoint list, next checkpoint index, lap count, and finish state.
• Current lap timer, best lap timer, total timer, paused flag, elapsed time, and random seed if any.
• Collision/debug state for tests.

Determinism and Evidence

• Evidence mode should inject acceleration and steering inputs, run long enough to move the car away from the start, and exit explicitly.
• Evidence outcome should include frame count, input count, car position, speed, heading, lap, next checkpoint, current time, and close reason.
• Screenshot evidence should show the track, car, start/finish line, checkpoint markers, and HUD.

Acceptance Criteria

• Car accelerates, brakes, steers, and slows due to drag.
• Car heading changes with steering while moving.
• Off-road slows the car relative to road.
• Wall or boundary collision prevents invalid movement.
• Checkpoints must be crossed in order before a lap counts.
• Lap timing starts and updates during play.
• Finish state appears after target laps.
• Pause freezes physics and timers.
• Interactive mode remains open until explicitly closed.

Out of Scope

• Multiple cars.
• Scrolling camera.
• Procedural track generation.
• Detailed tire simulation.
• Required audio.