Unity UGUI UITextUnderLinen Effect

UITextUnderLine

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

[ExecuteInEditMode]
[RequireComponent(typeof(Text))]
public class UnderLine : BaseMeshEffect
{
    private static readonly List<UIVertex> verts = new List<UIVertex>();
    private static readonly UIVertex[] data = new UIVertex[4];

    public Text text;

    public Color UnderlineColor = Color.black;
    public float LineOffset = 1;
    public float LineThickness = 2;

    protected UnderLine() { }

    protected override void Awake()
    {
        base.Awake();
        text = GetComponent<Text>();
        if (text.font == null)
        {
            Destroy(this);
            Debug.LogWarning("Text.font is null");
            return;
        }
        text.RegisterDirtyMaterialCallback(OnFontMaterialChanged);
        text.font.RequestCharactersInTexture("*", text.fontSize, text.fontStyle);
    }

    protected override void OnDestroy()
    {
        text.UnregisterDirtyMaterialCallback(OnFontMaterialChanged);
        base.OnDestroy();
    }

    private void OnFontMaterialChanged()
    {
        text.font.RequestCharactersInTexture("*", text.fontSize, text.fontStyle);
    }

    private Vector2 GetUnderlineCharUV()
    {

        //return Vector2.zero;
        var ch = '*';
        CharacterInfo info;
        //此处只是为了确保 动态Font的贴图准备好了 并没有其它意义
        if (text.font.GetCharacterInfo(ch, out info, text.fontSize, text.fontStyle))
        {       
            return (info.uvBottomLeft + info.uvBottomRight + info.uvTopLeft + info.uvTopRight) * 0.25f;
        }
        Debug.LogWarning("GetCharacterInfo failed");
        return Vector2.zero;
    }

    public override void ModifyMesh(VertexHelper vh)
    {
        if (!IsActive())
            return;
        if (vh.currentVertCount < 3)
            return;

        verts.Clear();
        vh.GetUIVertexStream(verts);

        var neededCpacity = verts.Count + 6;
        if (verts.Capacity < neededCpacity)
            verts.Capacity = neededCpacity;

        UIVertex vert = UIVertex.simpleVert;

        vh.PopulateUIVertex(ref vert, 3);
        var pos_a = vert.position;

        //此处计算最后一个顶点 verts.Count * 2 / 3 - 2公式是由mesh的共享顶点规则得到的 此处取到顶点的y轴 如果取的字符小 y的值
        //会很小 所以此处实际应该直接用fontsize来计算 再结合此处顶点的x轴坐标
        vh.PopulateUIVertex(ref vert, verts.Count * 2 / 3 - 2);

        var pos_b = vert.position;
        //此处的计算也可能会有偏差 当Text的Alignment不是Center时 注意额外的偏移计算
        var y = -text.fontSize / 2;

        var pos0 = new Vector3(pos_a.x, y - LineOffset);
        var pos1 = new Vector3(pos_b.x, y - LineOffset);
        var pos2 = new Vector3(pos_b.x, y - LineOffset - LineThickness);
        var pos3 = new Vector3(pos_a.x, y - LineOffset - LineThickness);

        vert.color = UnderlineColor;
        vert.uv0 = GetUnderlineCharUV();

        vert.position = pos0;
        data[0] = vert;
        vert.position = pos1;
        data[1] = vert;
        vert.position = pos2;
        data[2] = vert;
        vert.position = pos3;
        data[3] = vert;

        vh.AddUIVertexQuad(data);
    }
}