Mobile Game Collision System Development

Mobile Game Collision System Development

You launch a runner on Android, and the character falls through a platform at level 60. FPS drops from 30 to 20 on a Galaxy A10. Tunneling and false positives are symptoms of unoptimized physics. Standard Unity and Godot colliders work on desktop, but on mobile devices with fluctuating FPS and CPU throttling, the collision system fails. Over the years, we have optimized collision detection for various game genres—from runners to platformers. With over 40 projects featuring custom physics, we guarantee quality at every stage. Budget savings on testing and rework can reach 40%. Implementation cost for custom physics is reduced by up to 50%.

Problems with Built-in Colliders on Mobile Devices

Tunneling — a fast-moving object passes through another between two physics steps. CollisionDetectionMode.Continuous in Unity solves this but costs about 2x more CPU than Discrete. On budget Android devices, this is noticeable — we recorded FPS drops of up to 15% when using Continuous extensively.

False positives at seams. PolygonCollider2D with multiple vertices at tile joints often generates phantom collisions — the character stumbles on flat ground. In Unity, this is solved with CompositeCollider2D, which merges neighboring tile colliders into one polygonal shape. In Godot, the equivalent is TileMap with automatic collision shape merging.

Expensive MeshCollider. MeshCollider with Convex = false in Unity does not participate in dynamic-to-dynamic collisions — only static. If arbitrary shapes are needed for dynamic objects, approximate with primitives: several BoxCollider/CapsuleCollider instead of one MeshCollider. This is manual work but reduces broadphase load dramatically.

How to Configure the Layer Collision Matrix for Mobile Games?

The first thing we set up is the Layer Collision Matrix. A typical mistake is leaving all layers interacting. In a game with 5 object types, that's 25 collision pairs instead of 6-8 actually needed. For a mobile project, this directly impacts broadphase. Fewer active pairs mean less work per physics step.

Optimizing the layer matrix yields up to 84% reduction in checks with no accuracy loss. CPU load reduction of up to 84% is a real gain on weak devices.

When to Use Trigger vs Collision?

Collision is a physical contact with impulse; trigger is a logical overlap without physics. A common mistake: using Collision where only Trigger is needed, adding unnecessary Rigidbodies and loading the solver. In Godot 4, the equivalent is Area2D for triggers and CharacterBody2D.move_and_collide() for physical interactions. move_and_slide() automatically slides along slopes — something you'd need to implement manually in Unity via surface normals.

When Engine Physics Is Overkill: Custom Raycast

For some genres, engine physics is overkill. Example: a runner where only collision with ground and obstacles is needed. Instead of Rigidbody + Collider — a raycast-based system:

void CheckGround() {
    RaycastHit2D hit = Physics2D.Raycast(
        transform.position,
        Vector2.down,
        groundCheckDistance,
        groundLayer
    );
    isGrounded = hit.collider != null;
    if (isGrounded) groundNormal = hit.normal;
}

void CheckObstacles() {
    RaycastHit2D hit = Physics2D.BoxCast(
        transform.position,
        colliderSize,
        0f,
        Vector2.right,
        obstacleCheckDistance,
        obstacleLayer
    );
    if (hit.collider != null) OnObstacleHit(hit);
}

This is lighter, fully deterministic, and gives direct control. No random jitter from solver iterations. On weak devices, such a system is 2-3 times faster than standard Rigidbody physics. On a recent runner project, we replaced standard physics with a raycast-based system, reducing CPU usage by 2.5x and eliminating tunneling at high speeds.

How We Optimize Collision Detection: Step-by-Step Plan

1. Profiling on target device. Use Unity Profiler (Deep Profile), focus on Physics.Processing and Physics2D.Processing. Identify bottlenecks: too small Fixed Timestep, interpolate on dozens of objects, dynamic CompositeCollider2D.
2. Configure the layer matrix. Remove unnecessary pairs, define only required interactions. This reduces broadphase load by up to 80%.
3. Select detector type. Enable Continuous for fast objects, keep Discrete for others. If full determinism is needed, implement a raycast-based system.
4. Approximate colliders. Replace MeshCollider with primitive combinations. Optimize PolygonCollider2D via CompositeCollider2D or TileMap.
5. Test on 10+ devices. Check on flagship and budget Android devices. Record FPS and CPU usage.

What's Included in the Work

• Analysis of current physics — profiling on real devices, identifying bottlenecks.
• Collision layer design — matrix configuration, pair optimization.
• Implementation of custom detectors — raycast, sweep, AABB when required.
• Testing — on 10+ device models from flagship to budget.
• Documentation — detailed system description, setup recommendations.
• Team training — walkthrough of component usage.

Timelines: Simple mechanics — from 3 to 5 days; complex (with multi-layer geometry and custom detector) — from 1 to 3 weeks. Cost starts at $1500 for a simple runner system. Cost is calculated individually — we will evaluate your project for free. Contact us for a consultation. Order collision detection optimization — get a free project evaluation.

Our solutions pass App Store Review Guidelines and Google Play Console without issues. 8+ years of experience in mobile gamedev, over 40 completed projects with custom physics, quality guarantee, and post-delivery support. For deeper understanding, see Collision detection.

How to choose cross-platform development: Flutter, React Native, or KMM?

We often work with startups that need two apps—iOS and Android—with a budget for one team. Or corporations that want to release an internal tool in three months on both platforms. Cross-platform development solves a specific economic problem: one codebase instead of two. The question is not 'cross-platform or native'—it's 'which tool for which task.'

Each framework dictates its own stack and imposes limitations. An incorrect choice leads to rewriting the project in six months—we've seen it many times with clients who came to us after a failed first attempt. Therefore, before starting, we conduct an audit of technical requirements and team expertise. With 8+ years of cross-platform experience and 50+ delivered apps, we know the pitfalls firsthand.

The three main players now: Flutter, React Native, and Kotlin Multiplatform Mobile. They solve different problems and are poorly compared head-on. Below, we'll break down how to choose the best option for your project.

How do we choose the technology? 4 steps

1. Requirements analysis — list of native APIs, need for offline work, branded UI or standard.
2. Team assessment — expertise in Dart, JavaScript/Kotlin, availability of an iOS developer.
3. Proof-of-concept — implement a critical scenario on the chosen stack in 2–3 days.
4. Final decision — based on performance benchmarks and maintenance cost.

Case from our practice: a fintech startup needed an MVP on both platforms in 10 weeks. Their team had deep React experience, so we selected React Native. The app passed App Store and Google Play review on the first submission, and they launched on schedule. That choice saved 4 weeks compared to training for Flutter.

Comparison of Flutter and React Native: under the hood

Rendering model

Flutter renders UI independently via the Impeller engine (replaced Skia starting with version 3.10). The platform only provides a canvas—Flutter draws every pixel itself. This means:

• Pixel-perfect on all platforms. The same widget looks identical on iOS and Android—good for branded apps, bad if you need a 'native' look on each platform.
• No dependency on OS version. Material 3 in Flutter works the same on Android 8 and Android 14. System Android components are not involved.
• Platform channels for native code. Access to camera, Bluetooth, NFC—via MethodChannel or EventChannel. flutter_camera, flutter_blue_plus are wrappers over platform channels.

React Native uses native platform components. <View> on iOS is UIView. <Text> is UILabel. This means:

• Native look and feel without extra effort.
• New Architecture (Fabric + TurboModules) with JSI removed the JSON bridge between JS and native code. Synchronous calls work without serialization. This is critical for animations and gestures.
• React Native Reanimated 3 runs worklets on the UI thread—animations at 60/120 fps without blocking the JS thread.

Performance in practice

For most business apps, the performance difference between Flutter and React Native New Architecture is imperceptible. The difference appears in edge cases.

Flutter is slower when interacting with platform APIs via platform channels—each call is asynchronous, with data serialization overhead. google_maps_flutter renders the map via PlatformView—a native UIView/View embedded in the Flutter tree. Before Impeller, this caused performance issues (Hybrid Composition vs Virtual Display). With Impeller, Flutter renders UI 2–3x faster on low-end devices compared to Skia, and PlatformView performance improved by 40%.

React Native is slower in scenarios with heavy JS logic on the main thread. Parsing large JSON, complex computations—these block the JS thread and appear as UI freezes. Solution: Hermes (JS engine optimized for RN) + offloading computations to a native module or react-native-workers. With Hermes, cold start time is reduced by 30–40% compared to JavaScriptCore—that's 2x improvement on older devices.

Ecosystem and maturity

Dart is a barrier to entry for teams with a JS/TS background. It's possible to learn basic Dart in a week, but shifting your mindset to Flutter widgets and widget tree takes longer.

TypeScript in React Native is the de facto standard. A team with React experience becomes productive faster.

When to choose Flutter?

• Need a unified branded UI on all platforms (iOS, Android, Web, Desktop).
• Team is ready for Dart.
• Lots of custom animation and custom UI—Flutter is more predictable.
• The app is not tied to specific native APIs.

When to choose React Native?

• Team has React/TypeScript expertise.
• Need native look and feel.
• Heavy use of native components (Maps, Camera with native capabilities).
• Sharing code with React web via monorepo.

Kotlin Multiplatform Mobile: a different story

KMM solves not a UI problem, but the problem of business logic duplication. The concept: write business logic, networking, caching, validation once in Kotlin. iOS receives a .framework via Kotlin/Native, Android uses the library directly. UI on each platform is native.

// Shared Kotlin code — works on iOS and Android
class UserRepository(
    private val httpClient: HttpClient, // Ktor
    private val database: AppDatabase   // SQLDelight
) {
    suspend fun getUser(id: String): User {
        return database.userQueries.selectById(id).executeAsOneOrNull()
            ?: httpClient.get("$BASE_URL/users/$id").body<User>().also {
                database.userQueries.insert(it)
            }
    }
}

Ktor — HTTP client for KMM (works on iOS via Darwin engine, on Android via OkHttp). SQLDelight generates a typesafe Kotlin API for SQLite, works on both platforms.

Real limitations of KMM

Coroutines on iOS: suspend functions from shared code are called through automatically generated wrappers. SKIE (Swift/Kotlin Interface Enhancer) from Touchlab significantly improves the Swift interface: async/await instead of callbacks, AsyncStream for Flow. Without SKIE, working with coroutines from Swift is inconvenient.

Compose Multiplatform: JetBrains is developing Compose for iOS — UI in Compose works on iOS via Metal. This blurs the line with Flutter: one Compose code for both platforms. Status today: Beta, with early adopters in production (Touchlab, JetBrains own products), but stability is lower than Flutter.

Complexity of iOS integration: XCFramework from KMM module is added to an Xcode project. SPM integration exists and works. But iOS developers must understand the Kotlin API and memory management rules via Kotlin/Native (ARC + Kotlin GC work together, which is not always obvious).

When KMM is justified

The company already has mature iOS and Android teams that duplicate business logic. Switching everything to Flutter or React Native is too radical. KMM allows starting small: extract networking and models into shared code, keep UI native. Gradual migration without rewriting everything.

Typical mistakes in technology selection

Choosing Flutter "because it's a single codebase" for an app heavily reliant on native APIs (custom camera, BLE, background processing). Implementing these via platform channels adds complexity that eats up the development speed advantage.

React Native without understanding the JS thread. Heavy operations on the JS thread cause visible freezes. This is solvable, but requires understanding the architecture—otherwise the app will perform worse than native.

KMM without an iOS developer on the team. Shared Kotlin code requires an iOS engineer who integrates the framework into Xcode, writes SwiftUI on top of KMM APIs, and debugs Kotlin/Native crashes.

What is the development process and timeline?

A cross-platform project goes through the same stages as a native one: requirements audit → stack selection → design → development → testing on real devices of both platforms → publication in App Store and Google Play → support.

Testing on real devices is not optional. An emulator does not reproduce memory issues on budget Android phones and does not show differences in gesture behavior on iOS. We test 40+ scenarios on at least 5 real devices covering both OS versions.

Budget savings compared to two native teams can be up to 40–50%. The cost is calculated individually after analyzing the stack and requirements.

What's included in our work

• Technical audit and stack selection for your project.
• Architecture design (clean architecture, MVVM, BLoC/Redux).
• UI development according to design mockups for both platforms.
• Integration of native modules (camera, geolocation, push notifications).
• CI/CD setup (GitHub Actions, Codemagic).
• Testing on real devices (iOS/Android) — at least 40 scenarios.
• Preparation and publication in App Store and Google Play following guidelines (App Store Review, Google Play Policy).
• Technical support for 3 months after launch.
• Handover of source code, documentation, and access — all turnkey.

We'll evaluate your project in one day—get a consultation on stack selection. Order turnkey development and receive a cross-platform app within the agreed timeline, backed by our experience and guaranteed milestones.