Unity in Practice 0009 – How to Use Sprite Sheets in Unity for 2D Animation and UI

In Unity, a sprite sheet is a single image file that contains multiple smaller graphics (sprites), often used for 2D animation, character states, or tilemaps. It helps improve performance and makes organizing related sprites easier.

✅ Common Use Cases:

Character animation (walk / run / jump frames)
Environment tiles (grass, bricks, water, etc.)
UI elements (buttons, icons)

✅ How to Get and Import a Free Sprite Sheet

In this tutorial, we use a free asset from the Unity Asset Store: Warrior Free Asset | 2D Characters | Unity Asset Store

🧩 Steps to Add the Asset:

Open the asset’s page and click “Add to My Assets.”
Launch the project via Unity Hub — this will open the Unity Package Manager.

In the Package Manager, select the asset, then click Download and Import:

The imported Assets will be shown in the project window：

🧰 How to Use a Sprite Sheet in Unity:

Import the Sprite Sheet:
- Drag your image into the Unity Assets folder.
Set the Texture Type:
- Select the image.
- In the Inspector, set Texture Type to Sprite (2D and UI).
Set Sprite Mode:
- Change Sprite Mode to Multiple (instead of Single).
Open Sprite Editor:
- Click the Sprite Editor button.
- Use the Slice tool to divide the sheet into individual sprites.
  - Auto Slice = Unity tries to detect boundaries.
  - Manual Slice = You specify cell size or grid.
Apply Changes:
- Click Apply in the top right of the Sprite Editor.
Use Sprites in Your Game:
- Drag sliced sprites into the Scene.
- Use them in animations or as components in GameObjects.

Change the Pixels Per Unit of Sprite Sheet, from 100 to 16 in case the sprite is too small.

🎮 Add Sprite to the Scene

Rename the existing Ball sprite to Player.
Create an empty GameObject as a child of Player and name it Animator.
Add a Sprite Renderer component to the Animator GameObject.
Drag the first Warrior sprite from the asset pack into the Sprite Renderer’s Sprite field.

⚙️ Set Up Collider and Rigidbody for the Player

Remove the existing Circle Collider 2D from the Player GameObject.
Add a Capsule Collider 2D to the Player. Adjust its size if needed to match the Warrior sprite.
In the Rigidbody 2D component of Player, update the following properties:
- Collision Detection → set to Continuous
- Interpolate → set to Interpolate
- Freeze Rotation → check the box for Z Axis

🎬 Add Animation to the Animator GameObject

The imported Warrior asset already includes several animations and an Animator Controller.
Assign the Warrior’s Animator Controller to the Animator GameObject by dragging it into the Controller field of the Animator component.
Double-click the Animator Controller to open it in the Animator window.
In the Animator window, click the Parameters tab and add a new Bool parameter named IsRun.

🔁 Step 05: Add Transition Between Idle and Run

Open the Animator window
Double-click the Animator Controller to open it (Window > Animation > Animator).
Verify Animation States
Make sure both Idle and Run animations are present as states in the Animator graph.
Create Transitions
- Right-click on the Idle state and select “Make Transition”, then click on the Run state.
- Do the same from Run back to Idle.
Set Transition Conditions
- Click the Idle → Run transition.
- In the Inspector, under Conditions, click the + button.
- Select the IsRun parameter and set it to true.
- For the Run → Idle transition, add the condition IsRun equals false.
(Optional) Tweak transition settings
You can adjust transition duration and exit time if needed for smoother switching.

Final Code:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class BallScript : MonoBehaviour
{

    private Rigidbody2D rb;
    private Animator playerAnim;

    [SerializeField] private float moveSpeed;
    [SerializeField] private float jumpForce;

    private float xInput;
    [SerializeField] private bool isRun;

    // Start is called before the first frame update
    void Start()
    {
        rb = GetComponent<Rigidbody2D>();
        playerAnim = GetComponentInChildren<Animator>();
    }

    // Update is called once per frame
    void Update()
    {
        // Get horizontal input
        xInput = Input.GetAxis("Horizontal");

        // Apply horizontal movement
        rb.velocity = new Vector2(xInput * moveSpeed, rb.velocity.y);


        // Jump on Space key press
        if (Input.GetKeyDown(KeyCode.Space))
        {
            rb.velocity = new Vector2(rb.velocity.x, jumpForce);
        }

        isRun = rb.velocity.x != 0;

        playerAnim.SetBool("IsRun", isRun);
    }
}

Troubleshooting

Issue 1: When use Package Manager to add the asset, got following error:

[Package Manager Window] Error while getting auth code: System.InvalidOperationException: Failed to call Unity ID to get auth code.
UnityEditor.AsyncHTTPClient:Done (UnityEditor.AsyncHTTPClient/State,int)