Touch input basics in Unity - Performance & Optimization

Performance: Touch input basics

MEDIUM IMPACT

This concept affects how quickly and smoothly a game or app responds to user touch inputs, impacting input responsiveness and frame rate.

Handling touch input in a Unity game

Unity

void Update() {
  for (int i = 0; i < Input.touchCount; i++) {
    Touch touch = Input.GetTouch(i);
    if (touch.phase == TouchPhase.Began) {
      StartCoroutine(ProcessTouchAsync(touch));
    }
  }
}

IEnumerator ProcessTouchAsync(Touch touch) {
  // Spread heavy work over multiple frames
  for (int j = 0; j < 1000; j++) {
    // Simulate work
    if (j % 100 == 0) yield return null;
  }
}

Spreading heavy processing over multiple frames keeps input responsive and maintains frame rate.

📈 Performance GainAvoids blocking main thread, keeps frame time under 16ms, improving input responsiveness.

Handling touch input in a Unity game

Unity

void Update() {
  for (int i = 0; i < Input.touchCount; i++) {
    Touch touch = Input.GetTouch(i);
    if (touch.phase == TouchPhase.Began) {
      // Heavy processing here
      ProcessTouch(touch);
    }
  }
}

void ProcessTouch(Touch touch) {
  // Complex calculations or expensive operations
  for (int j = 0; j < 1000; j++) {
    // Simulate heavy work
  }
}

Heavy processing inside the Update loop for every touch causes frame drops and input lag.

📉 Performance CostBlocks rendering for 10-30ms per frame, causing dropped frames and poor responsiveness.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Heavy processing in Update	N/A	N/A	Blocks frame rendering causing lag	[X] Bad
Async processing with coroutines	N/A	N/A	Keeps frame rendering smooth	[OK] Good

Rendering Pipeline

Touch input is processed during the game loop before rendering each frame. Heavy input processing can delay frame updates, causing input lag and frame drops.

→Input Processing

→Game Logic Update

→Rendering

⚠️ BottleneckGame Logic Update when heavy processing blocks the main thread

Core Web Vital Affected

INP

This concept affects how quickly and smoothly a game or app responds to user touch inputs, impacting input responsiveness and frame rate.

Optimization Tips

1Avoid heavy processing directly inside Update during touch input.

2Use coroutines to spread expensive work over multiple frames.

3Monitor frame time in Unity Profiler to detect input lag.

Performance Quiz - 3 Questions

What is the main performance risk of doing heavy calculations directly inside the Update method when processing touch input?

A It can block the main thread and cause frame drops.

B It increases the app bundle size significantly.

C It causes the app to use more memory.

D It improves input responsiveness.

DevTools: Unity Profiler

How to check: Open Unity Profiler, run the game, and look at the CPU Usage timeline during touch input to see if Update spikes.

What to look for: High spikes in Update or main thread indicate blocking input processing causing frame drops.