PRD — Police Chase Arcade Game
Working title: Heatwave
Platform: iOS + Android
Engine: Unity
Genre: Top-down 3D arcade chase / survival
Orientation: Portrait
Input: One-thumb touch controls
Business model: TBD — design MVP around gameplay first
Primary goal: Build a genuinely fun playable prototype before adding progression or monetization.
⸻
Product vision
A fast, chaotic mobile arcade game where the player is constantly being pursued by increasingly aggressive police.
The player cannot directly attack.
Instead, they survive by driving aggressively, drifting around obstacles, making sudden turns and tricking pursuing police into crashing into obstacles and each other.
The fantasy is:
You’re not stronger than the police. You’re harder to catch.
Runs should produce constant near-misses, chain collisions and moments where the player escapes a seemingly impossible situation.
Think:
easy controls + aggressive pursuit + physics chaos + escalating pressure.
⸻
Core gameplay loop
START RUN
↓
DRIVE / DRIFT
↓
POLICE PURSUE
↓
BAIT POLICE
↓
DODGE
↓
POLICE CRASH
↓
GAIN SCORE
↓
WANTED LEVEL INCREASES
↓
MORE / HARDER POLICE
↓
SURVIVE
↓
EVENTUALLY GET CAUGHT
↓
SCORE / RESTART
Target run duration:
2–5 minutes.
Restart should take less than 2 seconds.
⸻
Design principles
3.1 One-thumb playable
The player should be able to understand the controls within seconds.
No accelerator.
No brake pedal.
No virtual steering wheel.
The vehicle moves automatically.
The player controls only direction.
(I moved away from this after testing it the first time and added the onscreen joystick)
3.2 Arcade physics, not simulation
Vehicles should:
drift
slide
bounce
spin
collide dramatically
recover quickly
Fun takes priority over physical accuracy.
3.3 Pursuers are weapons
Police are effectively the player’s offensive mechanic.
The player should learn:
“If I turn here, that cop is going straight into that wall.”
3.4 Chaos should remain readable
Even with 10+ vehicles on screen, the player must immediately understand:
where they are
where they’re moving
where police are coming from
what can kill them
3.5 Failure should feel fair
Death should generally result from a mistake the player understands rather than unpredictable physics.
⸻
MVP scope
Do not build progression, upgrades, missions or monetization for the first milestone.
The first version contains:
1 player vehicle
1 arena
1 police vehicle
1 elite police variant
5 wanted levels
physics collisions
environmental obstacles
scoring
player health
police destruction
basic VFX
basic audio
game-over screen
instant restart
That’s enough to determine whether the game deserves further development.
⸻
Player vehicle
Movement
Player vehicle uses a Rigidbody-based arcade controller.
Do not rely heavily on realistic WheelColliders.
Core variables should be exposed in the Unity Inspector:
Acceleration
Maximum Speed
Turn Speed
Turn Curve
Lateral Grip
Drift Factor
Vehicle Mass
Collision Force
Drag
Angular Drag
Recovery Speed
These need to be extremely easy to tune.
⸻
Controls
Recommended first implementation:
Drag steering
Player touches anywhere on the lower portion of the screen.
Dragging horizontally controls steering.
← drag turn left
→ drag turn right
Vehicle accelerates automatically.
Steering should be relative rather than absolute.
The player should be able to lift their finger without immediately losing control.
Alternative to prototype
Test:
Hold left/right side of screen = steer left/right.
Don’t commit until both have been tested on a physical phone.
⸻
Drift system
Drifting should happen naturally when turning at speed.
No dedicated drift button.
At low speed:
high traction
At high speed:
reduced lateral traction
This produces controlled sliding.
Long drifts can optionally award score.
Example:
DRIFT
+120
LONG DRIFT
+340
But drift scoring is secondary to police destruction.
⸻
Police AI
Police should feel:
aggressive, predictable and slightly stupid.
They should not simply follow the player’s current position.
Instead, calculate an interception target based on player velocity.
Conceptually:
target =
playerPosition
+
playerVelocity * predictionTime
Police therefore try to cut the player off.
⸻
Police intelligence
Police intentionally have limited obstacle avoidance.
This is important.
Perfect navigation would make the game less fun.
Police should:
pursue aggressively
attempt interception
avoid obvious static obstacles
poorly account for other police
overshoot turns
collide with each other
occasionally take dangerous routes
This creates opportunities for the player.
⸻
Police destruction
Police can be destroyed by:
high-speed obstacle collisions
hitting another police vehicle
chain collisions
environmental hazards
The player does not have weapons.
Example scoring:
COP SMASHED
+250
DOUBLE SMASH
+600
TRIPLE SMASH
+1,000
PILEUP!
+2,000
Chain collisions should be heavily rewarded.
⸻
Wanted system
Wanted level controls difficulty.
★☆☆☆☆
★★☆☆☆
★★★☆☆
★★★★☆
★★★★★
Wanted level increases based primarily on survival time and score.
Level 1
2 police.
Slow and forgiving.
Level 2
3–4 police.
Slightly faster.
Level 3
5–6 police.
More aggressive interception.
Level 4
7–9 police.
Elite police introduced.
Level 5
Maximum chaos.
10+ police depending on device performance.
Elite units appear frequently.
The game should eventually become effectively impossible.
That’s intentional.
⸻
Elite police
The MVP only needs one special police type.
Interceptor
Visually distinct vehicle.
Characteristics:
faster than standard police
lower mass
aggressive prediction
sharp steering
easier to destroy in collisions
This creates a glass-cannon pursuer.
⸻
Player health
Use a simple health bar.
Example:
HULL
██████░░░░
Minor impacts:
small damage.
Heavy impacts:
large damage.
Extremely high-speed impacts:
potential instant destruction.
Police contact alone shouldn’t immediately kill the player.
This allows chaotic scrambles.
⸻
Arena
First arena should be compact.
Something roughly equivalent to:
ROCK
┌─────────────┐
│ │
│ ROCK │
│ │
│ ███ │
│ │
│ ROCK │
│ ROCK│
└─────────────┘
Obstacles need enough space between them for high-speed movement.
Avoid procedural generation initially.
Hand-design one good arena.
⸻
Environment
For the first visual theme, I’d use something other than water so we’re not cloning the reference too closely.
My preference:
Desert outlaw chase
Player is an outlaw escaping through a stylized desert environment.
Environment contains:
rock formations
cacti
barriers
abandoned vehicles
ramps
fences
small buildings
dust
destructible props
It also fits the chunky visual language you’re already exploring with Bolt Pit.
⸻
Camera
Top-down perspective camera.
Not completely vertical.
Something approximately:
55–70° downward angle.
Camera follows player with smoothing.
Camera should look slightly ahead in the player’s travel direction.
At high speed:
camera pulls back slightly.
At low speed:
camera moves closer.
⸻
Camera juice
Small camera effects make a large difference.
Light collision
Tiny shake.
Heavy collision
Strong short shake.
Police destruction
Shake + tiny freeze frame.
Example:
50–100 ms hit stop.
Large pileup
Slight zoom impulse + shake + particles.
Don’t overdo continuous shaking.
⸻
Visual style
Chunky stylized 3D.
Characteristics:
simplified geometry
exaggerated proportions
bright readable vehicles
soft lighting
minimal textures
strong silhouettes
exaggerated particles
Avoid realistic vehicle proportions.
Cars should feel almost toy-like.
⸻
VFX
Minimum MVP effects:
Player
dust trail
tire/skid marks
drift smoke
impact sparks
Police
siren lights
smoke when damaged
destruction explosion
debris
Environment
dust
destructible objects
impact particles
⸻
Collision feedback
Every significant collision should combine:
physics + particles + audio + camera response.
Major police destruction:
IMPACT
→ physics impulse
→ vehicle fragments/debris
→ sparks
→ smoke
→ camera shake
→ hit stop
→ sound
→ score popup
This interaction is one of the game’s main sources of satisfaction.
⸻
Score system
Score comes from:
ActionExample
Surviving+10/sec
Police destroyed+250
Driftvariable
Near miss+100
Double collision+600
Triple collision+1,000
Large pileup+2,000
Exact values should remain configurable.
⸻
Near misses
Optional for MVP but potentially valuable.
Detect when a police vehicle passes extremely close to the player at high relative velocity.
Display:
CLOSE CALL! +100
This rewards risky driving.
⸻
UI
During gameplay keep UI extremely minimal.
SCORE COINS
13,590 14
★★★☆☆
WANTED
GAME
HULL
████████░░
No minimap initially.
Off-screen police can use subtle edge indicators.
⸻
Game over
When hull reaches zero:
brief slow motion.
Player crashes.
Then:
BUSTED
SCORE
24,850
BEST
31,220
[ AGAIN ]
Tapping anywhere could restart.
Avoid unnecessary menus between runs.
⸻
Audio
The soundscape should sell speed and collisions.
Required:
engine
tire squeal
police sirens
impact
metal crunch
debris
destruction
UI score sounds
wanted level increase
Sirens should become increasingly chaotic as wanted level increases.
⸻
Technical architecture
Suggested Unity structure:
GameManager
Player
├── PlayerController
├── VehiclePhysics
├── PlayerHealth
└── PlayerEffects
Police
├── PoliceController
├── PoliceAI
├── VehiclePhysics
├── PoliceHealth
└── PoliceEffects
Systems
├── SpawnManager
├── WantedManager
├── ScoreManager
├── AudioManager
├── CameraManager
└── PoolManager
UI
├── HUD
├── WantedUI
├── ScoreUI
├── HealthUI
└── GameOverUI
Avoid building an elaborate framework.
⸻
Object pooling
Police, particles and debris should use object pooling.
Avoid frequent:
Instantiate()
Destroy()
during gameplay.
Mobile performance should be considered from the beginning.
⸻
Performance target
Target:
60 FPS
on a mid-range modern iPhone/Android device.
Initial limits:
~12 active vehicles
~100 simple debris/particles
simple shadows
limited real-time lights
Performance should be tested on device early.
⸻
Development milestones
Milestone 1 — Greybox driving
Build:
empty arena
cube player
touch steering
acceleration
drifting
camera
Success criterion:
Driving around an empty arena feels satisfying.
Do not continue until it does.
⸻
Milestone 2 — The chase
Add:
one police vehicle
pursuit AI
interception
collisions
Success criterion:
Dodging one police car is entertaining.
⸻
Milestone 3 — Emergent chaos
Add:
multiple police
police-police collisions
obstacles
destruction
scoring
Success criterion:
Player can intentionally cause:
police → police
and
police → environment
collisions.
This is the critical milestone.
⸻
Milestone 4 — Escalation
Add:
wanted levels
spawning
difficulty scaling
interceptor
Now a run has an arc:
calm
↓
pressure
↓
chaos
↓
panic
↓
death
⸻
Milestone 5 — Juice
Add:
particles
camera shake
hit stop
skid marks
dust
sirens
collision sounds
score popups
⸻
Milestone 6 — Mobile build
Build for real devices.
Test:
controls
performance
readability
battery/thermal behaviour
different screen ratios
⸻
Milestone 7 — Decide whether to continue
At this point, stop development temporarily.
Don’t immediately build a garage and 37 unlockable cars.
Put the build in front of people.
The important questions are:
Do people immediately understand it?
Do they restart after dying?
Do they intentionally try to make cops crash?
Does “one more run” happen naturally?
If not, work on the core loop rather than adding content.
⸻
Phase 2 — only after validation
If the prototype works, then expand into:
Cars
↓
Coins
↓
Unlocks
↓
Challenges
↓
New arenas
↓
Special police
↓
Upgrades
↓
Daily challenges
↓
Leaderboards
Potential environments:
desert
city
docks
snow
industrial yard
airport
construction site
military base
And then there’s room for ridiculous police units: SUVs, armored vans, helicopters dropping roadblocks, etc.
I have opened a @[Unity CLI installation] project which we can work in. The art style of the game should be fun and cartoony and the action also over the top.
I have imported the Topdown engine into the project as well that we can use:
I want the game to be optimized for mobile, but should work on desktop while testing.
帖子正文
這段文字來自 X 原帖。
Top-down police chase arcade game prototype for mobile
Opus 5.5 built this game in @unity.
Artwork made in Chatgpt.
Used Topdown engine to speed up the process.
PROMPT:
PRD — Police Chase Arcade Game
Working title: Heatwave
Platform: iOS + Android
Engine: Unity
Genre: Top-down 3D arcade chase / survival
Orientation: Portrait
Input: One-thumb touch controls
Business model: TBD — design MVP around gameplay first
Primary goal: Build a genuinely fun playable prototype before adding progression or monetization.
⸻
Product vision
A fast, chaotic mobile arcade game where the player is constantly being pursued by increasingly aggressive police.
The player cannot directly attack.
Instead, they survive by driving aggressively, drifting around obstacles, making sudden turns and tricking pursuing police into crashing into obstacles and each other.
The fantasy is:
You’re not stronger than the police. You’re harder to catch.
Runs should produce constant near-misses, chain collisions and moments where the player escapes a seemingly impossible situation.
Think:
easy controls + aggressive pursuit + physics chaos + escalating pressure.
⸻
Core gameplay loop
START RUN
↓
DRIVE / DRIFT
↓
POLICE PURSUE
↓
BAIT POLICE
↓
DODGE
↓
POLICE CRASH
↓
GAIN SCORE
↓
WANTED LEVEL INCREASES
↓
MORE / HARDER POLICE
↓
SURVIVE
↓
EVENTUALLY GET CAUGHT
↓
SCORE / RESTART
Target run duration:
2–5 minutes.
Restart should take less than 2 seconds.
⸻
Design principles
3.1 One-thumb playable
The player should be able to understand the controls within seconds.
No accelerator.
No brake pedal.
No virtual steering wheel.
The vehicle moves automatically.
The player controls only direction.
(I moved away from this after testing it the first time and added the onscreen joystick)
3.2 Arcade physics, not simulation
Vehicles should:
drift
slide
bounce
spin
collide dramatically
recover quickly
Fun takes priority over physical accuracy.
3.3 Pursuers are weapons
Police are effectively the player’s offensive mechanic.
The player should learn:
“If I turn here, that cop is going straight into that wall.”
3.4 Chaos should remain readable
Even with 10+ vehicles on screen, the player must immediately understand:
where they are
where they’re moving
where police are coming from
what can kill them
3.5 Failure should feel fair
Death should generally result from a mistake the player understands rather than unpredictable physics.
⸻
MVP scope
Do not build progression, upgrades, missions or monetization for the first milestone.
The first version contains:
1 player vehicle
1 arena
1 police vehicle
1 elite police variant
5 wanted levels
physics collisions
environmental obstacles
scoring
player health
police destruction
basic VFX
basic audio
game-over screen
instant restart
That’s enough to determine whether the game deserves further development.
⸻
Player vehicle
Movement
Player vehicle uses a Rigidbody-based arcade controller.
Do not rely heavily on realistic WheelColliders.
Core variables should be exposed in the Unity Inspector:
Acceleration
Maximum Speed
Turn Speed
Turn Curve
Lateral Grip
Drift Factor
Vehicle Mass
Collision Force
Drag
Angular Drag
Recovery Speed
These need to be extremely easy to tune.
⸻
Controls
Recommended first implementation:
Drag steering
Player touches anywhere on the lower portion of the screen.
Dragging horizontally controls steering.
← drag turn left
→ drag turn right
Vehicle accelerates automatically.
Steering should be relative rather than absolute.
The player should be able to lift their finger without immediately losing control.
Alternative to prototype
Test:
Hold left/right side of screen = steer left/right.
Don’t commit until both have been tested on a physical phone.
⸻
Drift system
Drifting should happen naturally when turning at speed.
No dedicated drift button.
At low speed:
high traction
At high speed:
reduced lateral traction
This produces controlled sliding.
Long drifts can optionally award score.
Example:
DRIFT
+120
LONG DRIFT
+340
But drift scoring is secondary to police destruction.
⸻
Police AI
Police should feel:
aggressive, predictable and slightly stupid.
They should not simply follow the player’s current position.
Instead, calculate an interception target based on player velocity.
Conceptually:
target =
playerPosition
+
playerVelocity * predictionTime
Police therefore try to cut the player off.
⸻
Police intelligence
Police intentionally have limited obstacle avoidance.
This is important.
Perfect navigation would make the game less fun.
Police should:
pursue aggressively
attempt interception
avoid obvious static obstacles
poorly account for other police
overshoot turns
collide with each other
occasionally take dangerous routes
This creates opportunities for the player.
⸻
Police destruction
Police can be destroyed by:
high-speed obstacle collisions
hitting another police vehicle
chain collisions
environmental hazards
The player does not have weapons.
Example scoring:
COP SMASHED
+250
DOUBLE SMASH
+600
TRIPLE SMASH
+1,000
PILEUP!
+2,000
Chain collisions should be heavily rewarded.
⸻
Wanted system
Wanted level controls difficulty.
★☆☆☆☆
★★☆☆☆
★★★☆☆
★★★★☆
★★★★★
Wanted level increases based primarily on survival time and score.
Level 1
2 police.
Slow and forgiving.
Level 2
3–4 police.
Slightly faster.
Level 3
5–6 police.
More aggressive interception.
Level 4
7–9 police.
Elite police introduced.
Level 5
Maximum chaos.
10+ police depending on device performance.
Elite units appear frequently.
The game should eventually become effectively impossible.
That’s intentional.
⸻
Elite police
The MVP only needs one special police type.
Interceptor
Visually distinct vehicle.
Characteristics:
faster than standard police
lower mass
aggressive prediction
sharp steering
easier to destroy in collisions
This creates a glass-cannon pursuer.
⸻
Player health
Use a simple health bar.
Example:
HULL
██████░░░░
Minor impacts:
small damage.
Heavy impacts:
large damage.
Extremely high-speed impacts:
potential instant destruction.
Police contact alone shouldn’t immediately kill the player.
This allows chaotic scrambles.
⸻
Arena
First arena should be compact.
Something roughly equivalent to:
ROCK
┌─────────────┐
│ │
│ ROCK │
│ │
│ ███ │
│ │
│ ROCK │
│ ROCK│
└─────────────┘
Obstacles need enough space between them for high-speed movement.
Avoid procedural generation initially.
Hand-design one good arena.
⸻
Environment
For the first visual theme, I’d use something other than water so we’re not cloning the reference too closely.
My preference:
Desert outlaw chase
Player is an outlaw escaping through a stylized desert environment.
Environment contains:
rock formations
cacti
barriers
abandoned vehicles
ramps
fences
small buildings
dust
destructible props
It also fits the chunky visual language you’re already exploring with Bolt Pit.
⸻
Camera
Top-down perspective camera.
Not completely vertical.
Something approximately:
55–70° downward angle.
Camera follows player with smoothing.
Camera should look slightly ahead in the player’s travel direction.
At high speed:
camera pulls back slightly.
At low speed:
camera moves closer.
⸻
Camera juice
Small camera effects make a large difference.
Light collision
Tiny shake.
Heavy collision
Strong short shake.
Police destruction
Shake + tiny freeze frame.
Example:
50–100 ms hit stop.
Large pileup
Slight zoom impulse + shake + particles.
Don’t overdo continuous shaking.
⸻
Visual style
Chunky stylized 3D.
Characteristics:
simplified geometry
exaggerated proportions
bright readable vehicles
soft lighting
minimal textures
strong silhouettes
exaggerated particles
Avoid realistic vehicle proportions.
Cars should feel almost toy-like.
⸻
VFX
Minimum MVP effects:
Player
dust trail
tire/skid marks
drift smoke
impact sparks
Police
siren lights
smoke when damaged
destruction explosion
debris
Environment
dust
destructible objects
impact particles
⸻
Collision feedback
Every significant collision should combine:
physics + particles + audio + camera response.
Major police destruction:
IMPACT
→ physics impulse
→ vehicle fragments/debris
→ sparks
→ smoke
→ camera shake
→ hit stop
→ sound
→ score popup
This interaction is one of the game’s main sources of satisfaction.
⸻
Score system
Score comes from:
ActionExample
Surviving+10/sec
Police destroyed+250
Driftvariable
Near miss+100
Double collision+600
Triple collision+1,000
Large pileup+2,000
Exact values should remain configurable.
⸻
Near misses
Optional for MVP but potentially valuable.
Detect when a police vehicle passes extremely close to the player at high relative velocity.
Display:
CLOSE CALL! +100
This rewards risky driving.
⸻
UI
During gameplay keep UI extremely minimal.
SCORE COINS
13,590 14
★★★☆☆
WANTED
GAME
HULL
████████░░
No minimap initially.
Off-screen police can use subtle edge indicators.
⸻
Game over
When hull reaches zero:
brief slow motion.
Player crashes.
Then:
BUSTED
SCORE
24,850
BEST
31,220
[ AGAIN ]
Tapping anywhere could restart.
Avoid unnecessary menus between runs.
⸻
Audio
The soundscape should sell speed and collisions.
Required:
engine
tire squeal
police sirens
impact
metal crunch
debris
destruction
UI score sounds
wanted level increase
Sirens should become increasingly chaotic as wanted level increases.
⸻
Technical architecture
Suggested Unity structure:
GameManager
Player
├── PlayerController
├── VehiclePhysics
├── PlayerHealth
└── PlayerEffects
Police
├── PoliceController
├── PoliceAI
├── VehiclePhysics
├── PoliceHealth
└── PoliceEffects
Systems
├── SpawnManager
├── WantedManager
├── ScoreManager
├── AudioManager
├── CameraManager
└── PoolManager
UI
├── HUD
├── WantedUI
├── ScoreUI
├── HealthUI
└── GameOverUI
Avoid building an elaborate framework.
⸻
Object pooling
Police, particles and debris should use object pooling.
Avoid frequent:
Instantiate()
Destroy()
during gameplay.
Mobile performance should be considered from the beginning.
⸻
Performance target
Target:
60 FPS
on a mid-range modern iPhone/Android device.
Initial limits:
~12 active vehicles
~100 simple debris/particles
simple shadows
limited real-time lights
Performance should be tested on device early.
⸻
Development milestones
Milestone 1 — Greybox driving
Build:
empty arena
cube player
touch steering
acceleration
drifting
camera
Success criterion:
Driving around an empty arena feels satisfying.
Do not continue until it does.
⸻
Milestone 2 — The chase
Add:
one police vehicle
pursuit AI
interception
collisions
Success criterion:
Dodging one police car is entertaining.
⸻
Milestone 3 — Emergent chaos
Add:
multiple police
police-police collisions
obstacles
destruction
scoring
Success criterion:
Player can intentionally cause:
police → police
and
police → environment
collisions.
This is the critical milestone.
⸻
Milestone 4 — Escalation
Add:
wanted levels
spawning
difficulty scaling
interceptor
Now a run has an arc:
calm
↓
pressure
↓
chaos
↓
panic
↓
death
⸻
Milestone 5 — Juice
Add:
particles
camera shake
hit stop
skid marks
dust
sirens
collision sounds
score popups
⸻
Milestone 6 — Mobile build
Build for real devices.
Test:
controls
performance
readability
battery/thermal behaviour
different screen ratios
⸻
Milestone 7 — Decide whether to continue
At this point, stop development temporarily.
Don’t immediately build a garage and 37 unlockable cars.
Put the build in front of people.
The important questions are:
Do people immediately understand it?
Do they restart after dying?
Do they intentionally try to make cops crash?
Does “one more run” happen naturally?
If not, work on the core loop rather than adding content.
⸻
Phase 2 — only after validation
If the prototype works, then expand into:
Cars
↓
Coins
↓
Unlocks
↓
Challenges
↓
New arenas
↓
Special police
↓
Upgrades
↓
Daily challenges
↓
Leaderboards
Potential environments:
desert
city
docks
snow
industrial yard
airport
construction site
military base
And then there’s room for ridiculous police units: SUVs, armored vans, helicopters dropping roadblocks, etc.
I have opened a @[Unity CLI installation] project which we can work in. The art style of the game should be fun and cartoony and the action also over the top.
I have imported the Topdown engine into the project as well that we can use:
I want the game to be optimized for mobile, but should work on desktop while testing.