how to make a twisted sphere uniyt

Daniel Parker

2 min read

·

17-01-2025

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This tutorial will guide you through creating a twisted sphere mesh in Unity using C#. We'll achieve this effect by manipulating the vertices of a standard sphere mesh. This technique allows for a high degree of customization in the twisting effect.

Understanding the Approach

We'll start with a Unity sphere. Then, we'll write a script that iterates through each vertex of the sphere's mesh. For each vertex, we'll calculate a twist angle based on its position. Finally, we'll rotate the vertex around the sphere's Y-axis using this calculated angle. The result will be a sphere that appears twisted along its vertical axis.

Setting up the Scene

1. Create a new Unity project. Choose a 3D template.
2. Create a sphere: In the Hierarchy, right-click and select 3D Object > Sphere. Name it "TwistedSphere".
3. Create a C# script: Right-click in the Project window, select Create > C# Script, and name it "TwistSphere".

The C# Script (TwistSphere.cs)

using UnityEngine;

public class TwistSphere : MonoBehaviour
{
    public float twistAmount = 10f; // Adjust this value to control the twist intensity

    void Start()
    {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        Vector3[] vertices = mesh.vertices;
        Vector3[] newVertices = new Vector3[vertices.Length];

        for (int i = 0; i < vertices.Length; i++)
        {
            // Calculate the twist angle based on the vertex's Y position
            float yNormalized = (vertices[i].y + 0.5f) ; // Normalize y to 0-1 range
            float angle = yNormalized * Mathf.PI * twistAmount; // Scale by twistAmount and PI

            // Rotate the vertex around the Y-axis
            Vector3 rotatedVertex = Quaternion.AngleAxis(angle, Vector3.up) * vertices[i];
            newVertices[i] = rotatedVertex;
        }

        mesh.vertices = newVertices;
        mesh.RecalculateNormals();
        mesh.RecalculateBounds();
    }
}

Explaining the Code

• twistAmount: This public variable controls the intensity of the twist. Increase it for a stronger twist.
• Start(): This function runs once when the script is enabled.
• GetComponent<MeshFilter>().mesh: This line gets the mesh component of the sphere GameObject.
• vertices and newVertices: These arrays store the original and modified vertex positions.
• yNormalized: This variable normalizes the vertex's Y-coordinate to the range 0-1. This ensures that the twist is applied consistently regardless of the sphere's scale. Adding 0.5f centers the twist around the sphere's middle.
• angle: This calculates the twist angle based on the normalized Y-coordinate and the twistAmount.
• Quaternion.AngleAxis(angle, Vector3.up) * vertices[i]: This line rotates the vertex around the Y-axis using the calculated angle.
• mesh.vertices = newVertices: This line updates the sphere's mesh with the modified vertices.
• mesh.RecalculateNormals() and mesh.RecalculateBounds(): These lines are crucial. They recalculate the mesh's normals (surface orientation) and bounding box, which are necessary for proper rendering and collision detection.

Attaching the Script and Running

1. Attach the script: Drag the TwistSphere script from the Project window onto the TwistedSphere GameObject in the Hierarchy.
2. Adjust twistAmount: In the Inspector panel, adjust the twistAmount value to control the twist's intensity.
3. Run the game: Press the Play button to see the twisted sphere.

This approach creates a visually appealing twisted sphere effect. Experiment with different twistAmount values to achieve various levels of distortion. You can further extend this by adding more complex twisting algorithms, or twisting along different axes. Remember to always recalculate normals and bounds after modifying a mesh's vertices.