Circular widget in NGUI

using System.Collections.Generic;
using UnityEngine;

public class CustomSprite : UISprite
{
    public override void OnFill (List<Vector3> verts, List<Vector2> uvs, List<Color> cols)
    {
        var tex = mainTexture;
        if (tex == null) return;
        if (mSprite == null && GetAtlasSprite() == null) return;

        var outer = new Rect(mSprite.x, mSprite.y, mSprite.width, mSprite.height);
        var inner = new Rect(mSprite.x + mSprite.borderLeft, mSprite.y + mSprite.borderTop,
            mSprite.width - mSprite.borderLeft - mSprite.borderRight,
            mSprite.height - mSprite.borderBottom - mSprite.borderTop);

        outer = NGUIMath.ConvertToTexCoords(outer, tex.width, tex.height);
        inner = NGUIMath.ConvertToTexCoords(inner, tex.width, tex.height);

        var uv0 = new Vector2(inner.xMin, outer.yMin);
        var uv1 = new Vector2(inner.xMax, outer.yMax);

        var offset = verts.Count;
        var po = pivotOffset;
        var x0 = -po.x * mWidth;
        var y0 = -po.y * mHeight;
        var x1 = x0 + mWidth;
        var y1 = y0 + mHeight;

        var v = new Vector4(x0, y0, x1, y1);
        var c = drawingColor;
        var centerV = new Vector3((v.x + v.z) * 0.5f, (v.y + v.w) * 0.5f, 0f);

        const float c_thickness = 0.1f;
        const int c_slices = 90;

        var pi2 = Mathf.PI * 2f;

        for (int i = 0; i < c_slices; ++i)
        {
            var a0 = ((float)i / c_slices) * pi2;
            var a1 = ((float)(i + 1) / c_slices) * pi2;

            var c0 = Mathf.Cos(a0) * 0.5f + 0.5f;
            var c1 = Mathf.Cos(a1) * 0.5f + 0.5f;
            var s0 = Mathf.Sin(a0) * 0.5f + 0.5f;
            var s1 = Mathf.Sin(a1) * 0.5f + 0.5f;

            var v0 = new Vector3(Mathf.Lerp(v.x, v.z, c0), Mathf.Lerp(v.y, v.w, s0), 0f);
            var v1 = new Vector3(Mathf.Lerp(v.x, v.z, c1), Mathf.Lerp(v.y, v.w, s1), 0f);
            var v2 = Vector3.Lerp(v0, centerV, c_thickness);
            var v3 = Vector3.Lerp(v1, centerV, c_thickness);

            verts.Add(v0);
            verts.Add(v2);
            verts.Add(v3);
            verts.Add(v1);

            uvs.Add(uv1);
            uvs.Add(new Vector2(uv1.x, uv0.y));
            uvs.Add(uv0);
            uvs.Add(new Vector2(uv0.x, uv1.y));

            for (int b = 0; b < 4; ++b) cols.Add(c);
        }

        if (onPostFill != null) onPostFill(this, offset, verts, uvs, cols);
    }
}