Rendering preview window in Unity

PreviewData.cs

using UnityEngine;

[CreateAssetMenu(menuName ="Data/PreviewData")]
public class PreviewData : ScriptableObject
{
	public Color previewColor;
}

PreviewDataEditor.cs

using UnityEditor;
using UnityEngine;

namespace Assets.PreviewSceneTests
{
	[CustomEditor(typeof(PreviewData))]
	public class PreviewDataEditor : Editor
	{
		private PreviewSceneWindow preview;

		public override void OnInspectorGUI()
		{
			using (var changes = new EditorGUI.ChangeCheckScope())
			{
				base.OnInspectorGUI();

				if (changes.changed)
				{
					if (preview != null)
						preview.Refresh();
				}
			}

			if (GUILayout.Button("Preview"))
				preview = PreviewSceneWindow.Open(target as PreviewData);
		}
	}
}

PreviewObject.cs

using UnityEngine;

public class PreviewObject : MonoBehaviour
{
	[SerializeField] 
	private MeshRenderer meshRenderer;

	public void SetPreviewData(PreviewData data)
	{
		meshRenderer.sharedMaterial.color = data.previewColor;
	}
}

PreviewSceneWindow.cs

using UnityEditor;
using UnityEngine;

public class PreviewSceneWindow : EditorWindow
{
	public static PreviewSceneWindow Open(PreviewData data)
	{
		var window = GetWindow<PreviewSceneWindow>(typeof(SceneView));
		window.SetData(data);

		return window;
	}

	private PreviewData data;
	private PreviewRenderUtility preview;
	private PreviewObject previewObject;
	private Camera camera => preview.camera;

	public void OnEnable()
	{
		preview = new PreviewRenderUtility();

		SetupPreviewObject();

		SetupCamera();
	}

	public void OnDisable()
	{
		preview.Cleanup();
	}

	private void OnGUI()
	{
		DrawPreview();
	}

	public void Refresh()
	{
		previewObject.SetPreviewData(data);

		Repaint();
	}

	private void SetupPreviewObject()
	{
		previewObject = CreatePreviewObject();
		preview.AddSingleGO(previewObject.gameObject);
	}

	private void SetupCamera()
	{
		camera.farClipPlane = 100;
		camera.fieldOfView = 40;
		camera.transform.position = new Vector3(0, 0, -10);
	}

	private PreviewObject CreatePreviewObject()
	{
		var oreviewObject = Resources.Load<PreviewObject>("PreviewCube");
		return Instantiate(oreviewObject);
	}

	private void DrawPreview()
	{
		using (new GUILayout.VerticalScope())
			GUILayout.FlexibleSpace(); //This trick calculates the rect's dimensions

		var rect = GUILayoutUtility.GetLastRect();

		if (Event.current.type == EventType.Repaint)
		{
			preview.BeginPreview(rect, GUIStyle.none);
			preview.Render(true);

			var previewTexture = preview.EndPreview();
			GUI.DrawTexture(rect, previewTexture, ScaleMode.StretchToFill, false);
		}
		else if (Event.current.type == EventType.MouseDrag)
		{
			HandleMouseDrag();

			Repaint();
		}
	}

	private void HandleMouseDrag()
	{
		var drag = new Vector3(Event.current.delta.y, Event.current.delta.x, 0);

		var rotation = Quaternion.Euler(-drag);

		previewObject.transform.rotation *= rotation;
	}

	public void SetData(PreviewData data)
	{
		this.data = data;

		Refresh();
	}
}