代码参考如下：

using UnityEditor;
using UnityEditor.EditorTools;
using UnityEngine;

[EditorTool("Roaming View Tool", typeof(SetRoamingViewCtrl))]
public class RoamingViewTool : EditorTool
{
	public override GUIContent toolbarIcon => EditorGUIUtility.IconContent("EditCollider");

	public override void OnToolGUI(EditorWindow window)
	{
		if (window is not SceneView) return;
		// 
		foreach (var obj in targets)
		{
			if (obj is not SetRoamingViewCtrl setRoamingViewCtrl) continue;
			//
			Vector3[] nodes = setRoamingViewCtrl.nodes;
			//
			Handles.color = new Color(0, 1, 0, 0.5f);
			//
			for (int i = 0; i < nodes.Length; i++)
			{
				Vector3 node = setRoamingViewCtrl.nodes[i];

				EditorGUI.BeginChangeCheck();
				node = Handles.PositionHandle(node, Quaternion.identity);
				if (EditorGUI.EndChangeCheck())
				{
					Undo.RecordObject(setRoamingViewCtrl, "Moved roaming node");
					setRoamingViewCtrl.nodes[i] = node;
				}
				//
				int next = i + 1;
				next %= setRoamingViewCtrl.nodes.Length;
				Handles.DrawLine(setRoamingViewCtrl.nodes[i], setRoamingViewCtrl.nodes[next]);
			}
		}
	}
}

[EditorTool("Fixed View Tool", typeof(SetFixedViewCtrl))]
public class FixedViewTool : EditorTool
{
	public override GUIContent toolbarIcon => EditorGUIUtility.IconContent("AvatarPivot");

	public override void OnToolGUI(EditorWindow window)
	{
		if (window is not SceneView) return;
		// 
		foreach (var obj in targets)
		{
			if (obj is not SetFixedViewCtrl setFixedViewCtrl) continue;
			//
			for (int i = 0; i < setFixedViewCtrl.nodes.Length; i++)
			{
				Tran node = setFixedViewCtrl.nodes[i];

				EditorGUI.BeginChangeCheck();
				Quaternion rotation = node.rotation;
				Handles.TransformHandle(ref node.position, ref rotation);
				if (EditorGUI.EndChangeCheck())
				{
					Undo.RecordObject(setFixedViewCtrl, "Tran fixed node");
					Vector3 euler = rotation.eulerAngles;
					euler.z = 0;
					node.euler = euler;
				}
			}

			for (int i = 0; i < setFixedViewCtrl.nodes.Length; i++)
			{
				Tran node = setFixedViewCtrl.nodes[i];
				HandlesFrustum.Draw(node.position, node.rotation, 60, 3, 1.78f);
			}
		}
	}

	public class HandlesFrustum
	{
		static public void Draw(Vector3 center, Quaternion rotation, float fov, float range, float aspect)
		{
			Handles.matrix = Matrix4x4.TRS(center, rotation, Vector3.one);

			float z = Mathf.Abs(range);
			z = Mathf.Clamp(z, 0.1f, 100);

			fov = Mathf.Abs(fov * 0.5f);
			fov = Mathf.Clamp(fov, 1, 178);
			float y = z * Mathf.Tan(fov * Mathf.Deg2Rad);

			aspect = Mathf.Abs(aspect);
			aspect = Mathf.Clamp(aspect, 0.1f, 10);
			float x = y * aspect;

			Vector3 p0 = new Vector3(-x, -y, z);
			Vector3 p1 = new Vector3(-x, y, z);
			Vector3 p2 = new Vector3(x, y, z);
			Vector3 p3 = new Vector3(x, -y, z);
			Handles.DrawLine(Vector3.zero, p0);
			Handles.DrawLine(Vector3.zero, p1);
			Handles.DrawLine(Vector3.zero, p2);
			Handles.DrawLine(Vector3.zero, p3);
			Handles.DrawLine(p0, p1);
			Handles.DrawLine(p1, p2);
			Handles.DrawLine(p2, p3);
			Handles.DrawLine(p3, p0);
		}
	}
}

第8行中工具图标设置的字符串可参照下图：

或者参考链接：

Unity内置系统图标