How to draw a custom mesh in a UI.Graphic

SimpleGraphic.cs

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

[RequireComponent(typeof(CanvasRenderer))]
public class SimpleGraphic : MaskableGraphic //could extend Graphic if you don't need it maskable
{
	public Texture texture;
	
	public override Texture mainTexture
        {
            get {return texture;}
        }
	
	//if you set the texture from code, make sure to call this.SetMaterialDirty();
	//if you want to force the vertices to be redrawn, call this.SetVerticesDirty();
        
	protected override void OnPopulateMesh(VertexHelper vh)
	{
		float minX = (0f - rectTransform.pivot.x) * rectTransform.rect.width;
		float minY = (0f - rectTransform.pivot.y) * rectTransform.rect.height;
		float maxX = (1f - rectTransform.pivot.x) * rectTransform.rect.width;
		float maxY = (1f - rectTransform.pivot.y) * rectTransform.rect.height;

		var color32 = (Color32)color;

		vh.Clear();

		vh.AddVert(new Vector3(minX,minY), color32, new Vector2(0, 0));
		vh.AddVert(new Vector3(minX,maxY), color32, new Vector2(0, 1));
		vh.AddVert(new Vector3(maxX,maxY), color32, new Vector2(1, 1));
		vh.AddVert(new Vector3(maxX,minY), color32, new Vector2(1, 0));

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