
GrandTheftAuto Style.
A complete blueprint for building an open world crime sandbox. Car chases, police AI, gang missions, weapons, and a living city — all starting from zero.
Game Systems
Core
Mechanics.
Every system you need to build a believable open world crime sandbox.
01 // Open World
Living City Grid
A fully navigable urban environment with 4 distinct zones — downtown skyscrapers, desert highways, rural villages, and a restricted military area.

02 // Driving
Arcade Car Physics
Drift, brake, and boost through traffic. Rigidbody-based vehicle controller with realistic wheel friction and crash deformation.
03 // AI Chase
Police Pursuit AI
Wanted level system (1–5 stars). Police units spawn, radio for backup, and use roadblocks. Escape by losing line-of-sight.
04 // Missions
Objective System
Quest markers, NPC dialogue triggers, timed objectives, and fail states. Supports car chases, bank heists, and gang territory battles.
05 // Cycle
Day/Night System
Real-time directional lighting that rotates over 24 in-game minutes. NPCs change behavior, police visibility drops at night.
Recommended Engines
Pick Your
Stack.
1// GTAPrototype — Unity C# PlayerMovement.cs2// Attach to Player GameObject with Rigidbody component34using UnityEngine;56[RequireComponent(typeof(Rigidbody))]7public class PlayerMovement : MonoBehaviour8{9 [Header("Movement Settings")]10 public float walkSpeed = 5f;11 public float runSpeed = 10f;12 public float jumpForce = 6f;13 public float gravity = -20f;1415 [Header("Ground Check")]16 public Transform groundCheck;17 public float groundDistance = 0.4f;18 public LayerMask groundMask;1920 private Rigidbody rb;21 private bool isGrounded;22 private bool isRunning;2324 void Start()25 {26 rb = GetComponent<Rigidbody>();27 rb.freezeRotation = true;28 Cursor.lockState = CursorLockMode.Locked;29 }3031 void Update()32 {33 // Ground detection34 isGrounded = Physics.CheckSphere(35 groundCheck.position,36 groundDistance,37 groundMask38 );3940 isRunning = Input.GetKey(KeyCode.LeftShift);4142 // Jump43 if (Input.GetButtonDown("Jump") && isGrounded)44 {45 rb.AddForce(Vector3.up * jumpForce, ForceMode.Impulse);46 }47 }4849 void FixedUpdate()50 {51 float h = Input.GetAxis("Horizontal");52 float v = Input.GetAxis("Vertical");5354 float speed = isRunning ? runSpeed : walkSpeed;55 Vector3 move = transform.right * h + transform.forward * v;5657 rb.MovePosition(rb.position + move * speed * Time.fixedDeltaTime);5859 // Apply custom gravity60 if (!isGrounded)61 rb.AddForce(Vector3.up * gravity, ForceMode.Acceleration);62 }63}
Vehicle Roster
Ride Everything.
4 vehicle classes with distinct physics profiles and spawn locations.
180 mph
Sports Cars
High-speed pursuit vehicles. Fastest acceleration in the game.
160 mph
Motorcycles
Weave through traffic. Narrow profile for alley escapes.

80 mph
Heavy Trucks
Demolish roadblocks. Ram police cruisers. Slow but unstoppable.
140 mph
Police Cruisers
AI-controlled pursuit vehicles. Spawn at 2+ wanted stars.
Map Layout
4 Zones.
Each zone has distinct aesthetics, NPC density, and threat level.
Downtown Core
Skyscrapers, traffic gridlock, gang territories, and the city bank. Highest wanted level activity.
Desert Highway
Open road, sparse police presence. Ideal for high-speed chases and illegal drag races.
Rural Villages
Low-traffic zone. Hidden safehouses, weapons caches, and off-road terrain.

Military Restricted Area
Instant 5-star wanted level on entry. Military vehicles, helicopter pursuit, and tank spawns. End-game challenge zone.
Mission Ideas
Story
Missions.
4 mission templates ready to implement with objectives, steps, and reward structures.
Highway Pursuit
Objective
Intercept and destroy the armored van before it reaches the airport. 3-minute timer. Police spawn at 90 seconds.
Mission Steps
- 1.Steal a fast vehicle from the impound lot
- 2.Tail the van through downtown traffic
- 3.Force the van off the highway bridge
- 4.Escape with 3-star wanted level
First National Heist
Objective
Breach the vault, neutralize security, and escape via the underground tunnel before SWAT arrives in 6 minutes.
Mission Steps
- 1.Acquire disguises from the dry cleaner
- 2.Disable the alarm system remotely
- 3.Blow the vault door with C4
- 4.Drive the cash to the safehouse
Gang Territory War
Objective
Capture 3 territory control points in the Southside district. Hold each for 60 seconds against rival gang reinforcements.
Mission Steps
- 1.Eliminate the gang lookouts on the rooftop
- 2.Move to capture Point Alpha
- 3.Defend against 2 waves of reinforcements
- 4.Hold all 3 points simultaneously
Midnight Delivery
Objective
Deliver the unmarked package from the docks to the warehouse in the industrial zone. No weapons — stay off police radar.
Mission Steps
- 1.Pick up the package at Pier 7
- 2.Avoid police checkpoints on Route 9
- 3.Deliver to the warehouse before dawn
- 4.Collect payment from the contact
Development Roadmap
Next
Steps.
8 systems to build after the core prototype is running. Prioritized by gameplay impact.
Get Starter Code3D Characters
Rigged humanoid models with blend shape facial animations. Import Mixamo characters directly into Unity or Unreal.
Weapons System
Pistols, rifles, shotguns, and melee. Ammo management, reload animations, and bullet physics with Raycast hit detection.
Multiplayer Mode
Photon or Mirror networking for 2–8 players. Sync player positions, vehicle states, and mission objectives in real-time.
Story Mode
Branching narrative with 3 acts. Dialogue trees using Yarn Spinner. Player choices affect gang relationships and city state.
Traffic AI
NavMesh-based civilian vehicles that obey traffic lights, react to player chaos, and scatter during police chases.
Character Animation
Animator Controller with locomotion blend tree. Smooth transitions between walk, run, crouch, and combat stances.
Mobile Controls
Virtual joystick and HUD buttons for iOS/Android. Unity Input System with touch profile. 60fps mobile optimization.
Save System
JSON-based save files for player position, money, wanted level, and mission progress. Cloud sync via Unity Gaming Services.
Ready to build your open world?