open-project-1/UOP1_Project/Assets/Scripts/Editor/ClickToPlaceHelperEditor.cs

using UnityEditor;
using UnityEngine;

[CustomEditor(typeof(ClickToPlaceHelper))]
public class ClickToPlaceHelperEditor : Editor
{
	private ClickToPlaceHelper _clickHelper => target as ClickToPlaceHelper;

	public override void OnInspectorGUI()
	{
		base.OnInspectorGUI();

		if (GUILayout.Button("Place at Mouse cursor") && !_clickHelper.IsTargeting)
		{
			_clickHelper.BeginTargeting();
			SceneView.duringSceneGui += DuringSceneGui;
		}
	}

	private void DuringSceneGui(SceneView sceneView)
	{
		Event currentGUIEvent = Event.current;

		Vector3 mousePos = currentGUIEvent.mousePosition;
		float pixelsPerPoint = EditorGUIUtility.pixelsPerPoint;
		mousePos.y = sceneView.camera.pixelHeight - mousePos.y * pixelsPerPoint;
		mousePos.x *= pixelsPerPoint;

		Ray ray = sceneView.camera.ScreenPointToRay(mousePos);

		if (Physics.Raycast(ray, out RaycastHit hit))
		{
			_clickHelper.UpdateTargeting(hit.point);
		}

		switch (currentGUIEvent.type)
		{
			case EventType.MouseMove:
				HandleUtility.Repaint();
				break;
			case EventType.MouseDown:
				if (currentGUIEvent.button == 0) // Wait for Left mouse button down
				{
					_clickHelper.EndTargeting();
					SceneView.duringSceneGui -= DuringSceneGui;
					currentGUIEvent.Use(); // This consumes the event, so that other controls/buttons won't be able to use it
				}
				break;
		}
	}
}