Improved CircularTextMeshPro using OnPreRenderText

CircularTextMeshPro.cs

using UnityEngine;
using TMPro;
using Sirenix.OdinInspector;

/// <summary>
/// An extension of TextMeshPro that causes the text to be displayed in a
/// circular arc.
///
/// Adapted from https://github.com/TonyViT/CurvedTextMeshPro and improved.
/// TonyViT's version has some unnecessary properties and doesn't use the
/// OnPreRenderText event, which allows for fewer mesh updates.
/// </summary>
[ExecuteInEditMode]
[RequireComponent(typeof(TextMeshProUGUI))]
public class CircularTextMeshPro : MonoBehaviour {
    private TextMeshProUGUI m_TextComponent;

    [SerializeField, HideInInspector] private float m_radius = 10.0f;

    [ShowInInspector]
    [Tooltip("The radius of the text circle arc")]
    public float Radius {
        get => m_radius;
        set {
            m_radius = value;
            OnCurvePropertyChanged();
        }
    }

    private void Awake() {
        m_TextComponent = gameObject.GetComponent<TextMeshProUGUI>();
    }

    private void OnEnable() {
        m_TextComponent.OnPreRenderText += UpdateTextCurve;
        OnCurvePropertyChanged();
    }

    private void OnDisable() {
        m_TextComponent.OnPreRenderText -= UpdateTextCurve;
    }

    protected void OnCurvePropertyChanged() {
        UpdateTextCurve(m_TextComponent.textInfo);
        m_TextComponent.ForceMeshUpdate();
    }

    protected void UpdateTextCurve(TMP_TextInfo textInfo) {
        Vector3[] vertices;
        Matrix4x4 matrix;

        // Iterate over each character in the text
        for (int i = 0; i < textInfo.characterInfo.Length; i++) {
            // Skip invisible characters
            if (!textInfo.characterInfo[i].isVisible)
                continue;

            // Get the index of the mesh and material for the current character
            int vertexIndex = textInfo.characterInfo[i].vertexIndex;
            int materialIndex = textInfo.characterInfo[i].materialReferenceIndex;

            // Get the vertices of the mesh for the current character
            vertices = textInfo.meshInfo[materialIndex].vertices;

            // Calculate the midpoint of the character's baseline
            Vector3 charMidBaselinePos = new Vector2(
                (vertices[vertexIndex + 0].x + vertices[vertexIndex + 2].x) / 2,
                textInfo.characterInfo[i].baseLine);

            // Adjust the vertices' positions relative to the character's midpoint
            vertices[vertexIndex + 0] += -charMidBaselinePos;
            vertices[vertexIndex + 1] += -charMidBaselinePos;
            vertices[vertexIndex + 2] += -charMidBaselinePos;
            vertices[vertexIndex + 3] += -charMidBaselinePos;

            // Compute the transformation matrix for the current character
            matrix = ComputeTransformationMatrix(charMidBaselinePos, textInfo, i);

            // Apply the transformation matrix to each vertex of the character
            vertices[vertexIndex + 0] = matrix.MultiplyPoint3x4(vertices[vertexIndex + 0]);
            vertices[vertexIndex + 1] = matrix.MultiplyPoint3x4(vertices[vertexIndex + 1]);
            vertices[vertexIndex + 2] = matrix.MultiplyPoint3x4(vertices[vertexIndex + 2]);
            vertices[vertexIndex + 3] = matrix.MultiplyPoint3x4(vertices[vertexIndex + 3]);
        }
    }

    protected Matrix4x4 ComputeTransformationMatrix(Vector3 charMidBaselinePos, TMP_TextInfo textInfo, int charIdx) {
        // Calculate the radius for the current line
        float radiusForThisLine = m_radius + textInfo.lineInfo[textInfo.characterInfo[charIdx].lineNumber].baseline;

        // Calculate the circumference of the circle for the current line
        float circumference = 2 * radiusForThisLine * Mathf.PI;

        // Calculate the angle in radians based on the character's position and the circumference
        float angle = ((charMidBaselinePos.x / circumference - 0.5f) * 360 + 90) * Mathf.Deg2Rad;

        // Calculate the new x and y coordinates of the character's midpoint using sine and cosine
        float x0 = Mathf.Cos(angle);
        float y0 = Mathf.Sin(angle);

        // Create a new vector representing the new position of the character's midpoint
        Vector2 newMidBaselinePos = new Vector2(x0 * radiusForThisLine, -y0 * radiusForThisLine);

        // Calculate the rotation angle in degrees based on the character's new position
        float rotationAngle = -Mathf.Atan2(y0, x0) * Mathf.Rad2Deg - 90;

        // Create a transformation matrix using the new position, rotation, and scale
        return Matrix4x4.TRS(
            new Vector3(newMidBaselinePos.x, newMidBaselinePos.y, 0),
            Quaternion.AngleAxis(rotationAngle, Vector3.forward),
            Vector3.one
        );
    }
}

Hey. Any idea what could cause this behaviour? It's inconsistent and I'm not sure how to start debugging it. It's always some chars from the end. They pop out and warp in what seems to be a perpendicular direction

// Iterate over each character in the text
var min = Mathf.Min(textInfo.characterCount, textInfo.characterInfo.Length);
for (int i = 0; i < min; i++) {

is the solution to my issue btw