# Chapter 10: Fragnebt Post-Processing

**URL:** <https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053>\
**Category:** Metal by Tutorials\
**Created:** [November 16, 2020, 2:13pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053 "2020-11-16T14:13:42Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![richmond\_jam](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/richmond_jam/32/102075_2.png) [@richmond\_jam](https://forums.kodeco.com/u/richmond_jam)\
**Post date:** [November 16, 2020, 2:13pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053/1 "2020-11-16T14:13:42Z")

</div>

Hello Caroline, today I start to study the chapter 10, but I can not run the playground and I always receive this message: **Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file post\_processing\_Sources/Renderer.swift, line 271**  
So please tell me what can I do?

---

<div class="post-metadata">

**Author:** ![caroline](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/caroline/32/111867_2.png) [@caroline](https://forums.kodeco.com/u/caroline)\
**Post date:** [November 16, 2020, 5:33pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053/2 "2020-11-16T17:33:06Z")

</div>

Do you receive this error when you run the supplied final playground?

What is your hardware? (Device and GPU).

Version of macOS and Xcode?

---

<div class="post-metadata">

**Author:** ![richmond\_jam](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/richmond_jam/32/102075_2.png) [@richmond\_jam](https://forums.kodeco.com/u/richmond_jam)\
**Post date:** [November 16, 2020, 5:49pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053/3 "2020-11-16T17:49:22Z")

</div>

Hello Caroline, my version of macOS is Big Sur and my Xcode also newest version. I just want to try this final code with simulator

---

<div class="post-metadata">

**Author:** ![caroline](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/caroline/32/111867_2.png) [@caroline](https://forums.kodeco.com/u/caroline)\
**Post date:** [November 16, 2020, 10:24pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053/4 "2020-11-16T22:24:15Z")

</div>

Apple changed the way to make libraries in playgrounds.

In Renderer.swift, change line 169-171 to:

```auto
// guard let path = Bundle.main.path(forResource: "Shaders", ofType: "metal") else { return }
// let source = try String(contentsOfFile: path, encoding: .utf8)
// let library = try device.makeLibrary(source: source, options: nil)

let library = device.makeDefaultLibrary()!

```

---

<div class="post-metadata">

**Author:** ![kaitlynhwang](https://assets.chunter.kodeco.com/user_avatar/forums.kodeco.com/kaitlynhwang/32/105896_2.png) [@kaitlynhwang](https://forums.kodeco.com/u/kaitlynhwang)\
**Post date:** [July 1, 2021, 7:11pm UTC](https://forums.kodeco.com/t/chapter-10-fragnebt-post-processing/125053/5 "2021-07-01T19:11:20Z")

</div>

> [@caroline](#):
>
> ```auto
> let library = device.makeDefaultLibrary()!
> 
> ```

Issue still true for Big Sur 11.2.3 and Xcode Version 12.4 (12D4e). Updated the Renderer.swift lines 133-135. Works.