CircleCollider2DGizmo.cs

using UnityEditor;
using UnityEngine;

namespace Kogane.Internal
{
    internal static class CircleCollider2DGizmo
    {
        [DrawGizmo
        (
            GizmoType.NotInSelectionHierarchy |
            GizmoType.Selected |
            GizmoType.NonSelected
        )]
        private static void Draw
        (
            CircleCollider2D circleCollider2D,
            GizmoType        gizmoType
        )
        {
            var color    = Color.red;
            var width    = 8;
            var segments = 90;

            var transform = circleCollider2D.transform;
            var offset    = circleCollider2D.offset;
            var radius    = circleCollider2D.radius;
            var points    = new Vector3[ segments ];

            for ( var i = 0; i < segments; i++ )
            {
                var f = Mathf.Deg2Rad * ( i * 360f / ( segments - 1 ) );
                var x = offset.x + Mathf.Sin( f ) * radius;
                var y = offset.y + Mathf.Cos( f ) * radius;

                points[ i ] = transform.TransformPoint( new Vector3( x, y ) );
            }

            Handles.color = color;

            Handles.DrawAAPolyLine
            (
                lineTex: EditorGUIUtility.whiteTexture,
                width: width,
                points: points
            );
        }
    }
}