Reaction Chain: One Tap. One Explosion. Watch Everything Die.
You get one tap.
Colorful circles drift across your screen — bouncing off walls, gently pulling toward each other, clustering and separating in lazy orbits. They are alive. They are beautiful. And your job is to destroy as many of them as possible with a single touch.
Tap the screen. An explosion appears. If it reaches a circle, that circle detonates too. Its explosion reaches the next circle. That one detonates. Chain reaction. The screen fills with cascading fireballs, expanding shockwaves, and particle showers as circle after circle erupts in sequence.
Or you tap in the wrong spot and one lonely explosion fizzles out while 30 untouched circles float by, indifferent.
Reaction Chain is a game about patience, positioning, and the deep human satisfaction of watching a perfectly timed catastrophe unfold.
How It Works
Each level drops a set of colorful circles onto the screen. They move. They bounce. They drift toward each other. You watch. You wait. You tap once.
Your tap creates an explosion with an 80-pixel blast radius. If any circle’s edge falls within that radius during the explosion’s active phase, that circle detonates and creates its own 80-pixel explosion. If that secondary explosion touches another circle, the chain continues. And continues. And continues.
When the chain reaction burns out — when no active explosions are touching any surviving circles — the level ends. The game counts how many circles you destroyed and compares it to the level’s target percentage.
Pass the target and you advance. Fail and you retry. That is the entire game. One tap per level. Infinite levels. No undo.
Level Scaling
Every level increases in two dimensions: more circles to destroy, and a higher percentage required to pass.
| Level | Circle Count | Target % | Required Kills | Circle Speed |
|---|---|---|---|---|
| 1 | 7 | 62% | 5 of 7 | 35 px/s |
| 5 | 15 | 70% | 11 of 15 | 55 px/s |
| 10 | 25 | 80% | 20 of 25 | 80 px/s |
| 15 | 35 | 90% | 32 of 35 | 105 px/s |
| 18+ | 40 (max) | 90% (max) | 36 of 40 | 120+ px/s |
The circle count formula is 5 + level * 2, capped at 40. The target percentage is 60 + level * 2, capped at 90%. Circle base speed starts at 35 px/s and increases by 5 px/s per level, with individual circles varying between 60% and 140% of that base speed.
Early levels are generous — 7 circles, 62% target, you need to catch 5 of them. This is almost impossible to fail. By level 15, you need 32 out of 35 circles with a single tap. The margin for error becomes razor-thin.
The Star System
Each level awards zero to three stars based on your destruction percentage:
| Destruction % | Stars | Meaning |
|---|---|---|
| Below target | 0 | Failed — retry |
| Target – 79% | 1 | Passed |
| 80 – 99% | 2 | Great |
| 100% | 3 | Perfect — bonus |
A 100% clear (every single circle destroyed) awards a 50-point score bonus on top of the percentage score. Three stars on a high-level stage means your single tap triggered a chain reaction that consumed every circle on the screen. No survivors. Total annihilation from one touch.
Chasing three stars on every level is where the real game lives. Passing a level is easy enough with patience. Perfecting it requires understanding the gravity system, reading the cluster patterns, and placing your tap with surgical precision.
The Gravity Mechanic: Why Circles Cluster
This is the feature that elevates Reaction Chain from “tap and hope” to “tap with intent.”
Every circle exerts a gentle gravitational pull on nearby circles. When two circles are within 150 pixels of each other (but not overlapping), they accelerate toward one another with a force proportional to the inverse square of their distance — the same law that governs planetary orbits, scaled down to a phone screen.
The gravitational constant is 20.0, applied over a 1000x multiplier for game-scale effect. The result: circles that start evenly distributed across the screen will gradually form clusters. They drift together, orbit each other at close range, and create dense pockets of targets separated by empty space.
This clustering is the entire strategic layer of the game. A circle in the middle of a tight cluster is worth exponentially more than a circle floating alone at the edge of the screen. Your tap does not need to touch every circle — it needs to touch one circle that is close enough to others to start a chain that reaches every cluster.
Velocity is capped at 300 px/s to prevent circles from gravity-slingshotting off the screen. They also bounce off all four screen edges, which keeps the play area contained and creates natural convergence points in corners and along walls.
The circles pulse gently — their display radius oscillates by plus or minus 2 pixels on a sinusoidal cycle. This does not affect gameplay, but it makes the circles feel organic and alive. They breathe. Destroying them feels like ending something that was moving with purpose.
The Explosion Physics
Explosions are the visual and mechanical centerpiece of the game. Each one goes through four phases:
Growing (0.5 seconds): The explosion expands from radius 0 to its maximum of 80 pixels following an ease-out curve. It starts fast and decelerates, creating a punchy initial burst. During this phase, the explosion can trigger chain reactions on contact.
Staying (0.3 seconds): The explosion holds at maximum radius. Still triggering chains. This is the window where nearby circles that were almost out of range might drift close enough to catch.
Fading (0.3 seconds): The explosion’s opacity drops to zero over 0.3 seconds. It can no longer trigger chains. It is purely visual at this point — the fireball cooling into nothing.
Done: The explosion is removed from the simulation.
The total active trigger window is 0.8 seconds (growing + staying). During that window, any living circle whose edge intersects the explosion radius will detonate. The 0.8-second window is critical — it means explosions overlap temporally. A circle that detonates at the end of one explosion’s active phase creates a new explosion whose 0.8-second window extends the chain’s total lifetime. Long chains can persist for several seconds, with explosions rippling across the screen in waves.
Each explosion spawns 8-13 particles that fly outward at 60-180 px/s in random directions. Particles live for 0.5 to 1.0 seconds and decelerate via a 0.97x friction multiplier per frame. They do not affect gameplay. They exist entirely to make the chain reaction look spectacular — and they succeed.
A ripple ring expands outward from each explosion at 200 px/s, fading as it grows. Chain lines — white connecting strokes — briefly flash between the triggering explosion and the newly detonated circle, visualizing the chain of causality. For 0.3 seconds, you can see exactly which explosion caused which detonation. This visual storytelling is what makes watching a chain reaction so satisfying: you can trace the path of destruction from your original tap through every subsequent explosion.
The Rendering
The visual stack is layered for maximum impact.
Circles are drawn with radial gradient fills — a lighter highlight offset to the upper-left simulates a light source and gives them dimensionality. Each circle has a soft 12-pixel blur glow in its base color, creating a neon halo effect against the dark background. When an active explosion is within 30 pixels of an alive circle, a red danger glow stroke appears around it — a warning flash that the chain is about to consume it.
Explosions render as four concentric elements: a white-hot core with an 8-pixel blur, an inner gradient from pale yellow through orange to transparent, a white outer ring, and a secondary amber ring at 70% radius. The effect is layered light — a bright center fading to warm edges, exactly how a real fireball looks.
The color palette cycles through 8 carefully chosen colors — coral, gold, lime, cyan, pink, orange, lavender, and mint. These are high-saturation, high-contrast colors that read instantly against the dark background and create a visually chaotic but beautiful explosion cascade when multiple circles detonate simultaneously.
Strategy Tips
Wait for clusters, not positions. The gravity mechanic means circles are always moving toward each other. A spread-out field at the start of a level will naturally compress into clusters if you give it time. Patience is literally rewarded by the physics engine.
Tap between clusters, not on them. Your initial explosion has the same 80-pixel radius as chain explosions. Place it in the gap between two dense clusters so the blast radius overlaps both. One well-placed interstitial tap can ignite two chains simultaneously.
Watch the edges. Circles bounce off screen boundaries, which means edges and especially corners are natural clustering zones. A tap near a corner can catch circles that have been compressed against the wall by gravity.
Count before you tap. On high levels where you need 90% destruction, a single missed circle is the difference between one star and zero. Visually estimate which circles are isolated and which are connected. If a circle is far from any cluster with no gravitational neighbors, accept that it might survive and place your tap to maximize the connected group.
The 0.8-second window is your friend. Explosions stay active long enough for nearby circles to drift into range. If a circle is just outside blast radius but moving inward due to gravity, it might catch the tail end of the staying phase. Factor in circle movement when choosing your tap point — not just where circles are, but where they are heading.
Chase three stars on early levels. Low-level stages with 7-15 circles are the most realistic candidates for 100% destruction and the 50-point bonus. Perfect them before grinding higher levels.
Why One Tap Works
The constraint of a single tap transforms every level into a puzzle. If you could tap multiple times, the game would be a whack-a-mole variant — reactive, imprecise, noisy. One tap forces deliberation. You watch the circles move. You read the gravity patterns. You visualize the chain. You commit.
And then you watch the result play out with zero control. The chain either reaches everything or it does not. The explosions cascade or they fizzle. That moment between tapping and seeing the outcome is pure anticipation — the same dopamine mechanics that make slot machines and domino toppling videos go viral.
Except unlike a slot machine, the outcome is not random. It is entirely determined by your read of the situation and the precision of your placement. Skill, patience, physics. One tap.
The Infinite Climb
There is no final level. The circle count caps at 40 and the target caps at 90%, but the levels keep incrementing. Circle speed keeps climbing. The clusters form and break apart faster. The window for a perfect tap gets shorter and shorter as the physics simulation speeds up.
The leaderboard is your best level reached. The bragging right is your star count. And the replay value is the certain knowledge that your last level’s 87% could have been a 100% if you had just waited one more second for that lone orange circle to drift into the cluster.
Built With
- Flutter — Cross-platform framework running custom game loop at 60fps
- Dart — Physics simulation with gravitational attraction, velocity capping, and wall-bounce collision
- CustomPainter — Full-canvas rendering for circles, explosions, particles, chain lines, and glow effects
- Inverse-square gravity — Real gravitational math creating emergent clustering behavior
- Phased explosion system — 4-phase lifecycle (grow, stay, fade, done) with precise 0.8s trigger window
- Particle engine — 8-13 particles per explosion with friction deceleration and opacity fade
- 8-color palette — Curated high-saturation colors for maximum visual impact during chain cascades
Watch the circles. Read the clusters. One tap. Total destruction. Click here to download for free.