Touch input basics in Unity - Step-by-Step Execution

Concept Flow - Touch input basics

Start Frame

↓

Check Touch Count > 0?

No→No Touch Detected

Yes↓

Get Touch Data (position, phase)

↓

Process Touch Based on Phase

↓

Respond to Touch (move, tap, etc.)

↓

End Frame / Wait Next Frame

Each frame, Unity checks if the screen is touched. If yes, it reads touch details and reacts based on touch state.

Execution Sample

Unity

void Update() {
  if (Input.touchCount > 0) {
    Touch touch = Input.GetTouch(0);
    if (touch.phase == TouchPhase.Began) {
      Debug.Log($"Touch started at {touch.position}");
    }
  }
}

This code checks if the screen is touched and logs the position when a new touch begins.

Execution Table

Step	Input.touchCount	Touch Index	Touch.phase	Condition	Action	Output
1	0	-	-	0 > 0?	No	No touch detected, nothing happens
2	1	0	Began	1 > 0?	Yes	Touch detected, check phase
3	1	0	Began	phase == Began?	Yes	Log touch start position
4	1	0	Moved	phase == Began?	No	No log, touch moved
5	0	-	-	0 > 0?	No	No touch detected, nothing happens

💡 When touchCount is 0, no touch is detected and code skips touch processing.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5
Input.touchCount	0	1	1	1	0
touch.phase	-	Began	Began	Moved	-
Condition (touch.phase == Began)	-	True	True	False	-

Key Moments - 3 Insights

Why does the code check if Input.touchCount > 0 before getting touch data?

Because if there are no touches, trying to get touch data causes errors. The execution_table row 1 shows no touch detected when touchCount is 0.

What does TouchPhase.Began mean and why is it important?

TouchPhase.Began means the finger just touched the screen. The code reacts only at this phase to detect new touches, as shown in execution_table rows 2 and 3.

Why doesn't the code log anything when the touch phase is Moved?

Because the condition checks for Began phase only. When phase is Moved (row 4), the condition is false, so no log happens.

Visual Quiz - 3 Questions

Look at the execution_table, what is Input.touchCount at Step 2?

A 1

B 0

C 2

D -

💡 Hint

Check the Input.touchCount column at Step 2 in the execution_table.

At which step does the code log the touch start position?

A Step 4

B Step 1

C Step 3

D Step 5

💡 Hint

Look for the Output column mentioning logging in the execution_table.

If Input.touchCount was never checked, what would happen when no touches exist?

A Code runs normally

B Error occurs trying to get touch data

C Touch phase is always Began

D TouchCount becomes negative

💡 Hint

Refer to key_moments about why checking touchCount is necessary.

Concept Snapshot

Unity Touch Input Basics:
- Check Input.touchCount > 0 each frame
- Use Input.GetTouch(index) to get touch info
- Touch.phase tells touch state (Began, Moved, Ended)
- React to phases to handle touch events
- Always check touchCount before accessing touches

Full Transcript

In Unity, touch input is checked every frame by looking at Input.touchCount. If it is greater than zero, the program reads the first touch using Input.GetTouch(0). The touch has a phase property that tells if the touch just began, moved, or ended. The example code logs the position only when the touch phase is Began, meaning a new finger just touched the screen. If no touches exist, the code skips processing to avoid errors. This flow ensures safe and correct touch input handling.