unity : use tight sprite atlas in canvas as image

TightImage.cs

using UnityEngine;
using UnityEngine.UI;

public class TightImage : Image
{
    private RectTransform mRect;

    private RectTransform RectTransform
    {
        get
        {
            if (mRect == null)
            {
                mRect = GetComponent<RectTransform>();
            }

            return mRect;
        }
    }

    protected override void OnPopulateMesh(VertexHelper toFill)
    {
        if (type == Type.Simple)
        {
            toFill.Clear();
            DoPopulateSimpleImage(toFill);
        }
        else
        {
            base.OnPopulateMesh(toFill);
        }
    }

    private void DoPopulateSimpleImage(VertexHelper toFill)
    {
        var spColor = color;

        var r = GetPixelAdjustedRect();
        var bounds = overrideSprite.bounds;

        var scaleX = r.width / bounds.size.x;
        var scaleY = r.height / bounds.size.y;

        if (preserveAspect)
        {
            var minScale = Mathf.Min(scaleX, scaleY);
            scaleX = scaleY = minScale;
        }

        var offsetImgX = RectTransform.rect.center.x;
        var offsetImgY = RectTransform.rect.center.y;

        var offsetSpX = -scaleX * bounds.center.x;
        var offsetSpY = -scaleY * bounds.center.y;


        for (var i = 0; i < overrideSprite.vertices.Length; i++)
        {
            var x = overrideSprite.vertices[i].x * scaleX + offsetImgX + offsetSpX;
            var y = overrideSprite.vertices[i].y * scaleY + offsetImgY + offsetSpY;
            toFill.AddVert(new Vector3(x, y, 0), spColor, overrideSprite.uv[i]);
        }

        var triangles = overrideSprite.triangles;
        for (var i = 0; i < triangles.Length; i += 3)
        {
            toFill.AddTriangle(triangles[i], triangles[i + 1], triangles[i + 2]);
        }
    }
}