memo UI上で動的に矢印の生成。

using UnityEngine;
using UnityEngine.UI;

public class ArrowRenderer : Graphic
{
    protected override void OnPopulateMesh(VertexHelper vh)
    {
        Vector2 corner1 = Vector2.zero;
        Vector2 corner2 = Vector2.zero;

        Vector2 leftBottom = Vector2.zero;
        Vector2 rightBottom = Vector2.zero;
        Vector2 top = Vector2.zero;

        corner1.x = 0f;
        corner1.y = 0f;
        corner2.x = 1f;
        corner2.y = 1f;

        leftBottom.x = -0.2f;
        leftBottom.y = 0f;

        rightBottom.x = 1.2f;
        rightBottom.y = 0f;

        top.y = -0.3f;
        top.x = 0.5f;


        corner1.x -= rectTransform.pivot.x;
        corner1.y -= rectTransform.pivot.y;
        corner2.x -= rectTransform.pivot.x;
        corner2.y -= rectTransform.pivot.y;

        leftBottom.x -= rectTransform.pivot.x;
        leftBottom.y -= rectTransform.pivot.y;

        rightBottom.x -= rectTransform.pivot.x;
        rightBottom.y -= rectTransform.pivot.y;

        top.y -= rectTransform.pivot.y;
        top.x -= rectTransform.pivot.x;


        corner1.x *= rectTransform.rect.width;
        corner1.y *= rectTransform.rect.height;
        corner2.x *= rectTransform.rect.width;
        corner2.y *= rectTransform.rect.height;

        leftBottom.x *= rectTransform.rect.width;
        leftBottom.y *= rectTransform.rect.height;

        rightBottom.x *= rectTransform.rect.width;
        rightBottom.y *= rectTransform.rect.height;

        top.y *= rectTransform.rect.height;
        top.x *= rectTransform.rect.width;

        vh.Clear();

        UIVertex vert = UIVertex.simpleVert;

        vert.position = new Vector2(corner1.x, corner1.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vert.position = new Vector2(corner1.x, corner2.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vert.position = new Vector2(corner2.x, corner2.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vert.position = new Vector2(corner2.x, corner1.y);
        vert.color = Color.black;
        vh.AddVert(vert);


        vert.position = new Vector2(leftBottom.x, leftBottom.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vert.position = new Vector2(rightBottom.x, rightBottom.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vert.position = new Vector2(top.x, top.y);
        vert.color = Color.black;
        vh.AddVert(vert);

        vh.AddTriangle(0, 1, 2);
        vh.AddTriangle(2, 3, 0);
        vh.AddTriangle(4, 5, 6);
    }
}