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+# Chapter 20: Advanced Lighting
+
+As I read this book, I summarize what I think is wrong. If you think my comments are wrong then please let me know. We can dicuss more and update your opinion.
+
+## Getting started
+
+There is a runtime error in because Shaders.metal files isn't included in the bundle. But we have the default library.
+
+In Renderer.swift, in initializeMetal(), replace this:
+
+```
+guard let path = Bundle.main.path(forResource: "Shaders", ofType: "metal") else { fatalError() }
+let input = try String(contentsOfFile: path, encoding: String.Encoding.utf8)
+let library = try device.makeLibrary(source: input, options: nil)
+```
+
+With:
+
+```
+let library = device.makeDefaultLibrary()!
+```
+
+## Drawing a checkerboard pattern
+
+This book explains the different between truncated division and floored division but it's not cinch to understand. Below figure will help you understand easily.
+
+![](./difference-divisions.jpeg)
+
+## Refraction
+
+There is a runtime error in because Shaders.metal files isn't included in the bundle. But we have the default library.
+
+In Renderer.swift, in initializeMetal(), replace this:
+
+```
+guard let path = Bundle.main.path(forResource: "Shaders", ofType: "metal") else { fatalError() }
+let input = try String(contentsOfFile: path, encoding: String.Encoding.utf8)
+let library = try device.makeLibrary(source: input, options: nil)
+```
+
+With:
+
+```
+let library = device.makeDefaultLibrary()!
+```
+
+## Raytraced water
+
+There is a runtime error in because Shaders.metal files isn't included in the bundle. But we have the default library.
+
+In Renderer.swift, in initializeMetal(), remove this:
+
+```
+let path = Bundle.main.path(forResource: "Shaders", ofType: "metal")
+```
+
+Replace this:
+
+```
+let input = try String(contentsOfFile: path!, encoding: String.Encoding.utf8)
+let library = try device!.makeLibrary(source: input, options: nil)
+```
+
+With:
+
+```
+let library = device.makeDefaultLibrary()!
+```
+
+## 3. Clipping planes
+
+This book uses vector_float4 to define a clip plane without any explanation. The plane consists of the normal of plane and the distance from the origin. From a below figure, we can know the plane can be represented by `ax + by + cz + d = 0`. You can get more detail at [here](https://brilliant.org/wiki/3d-coordinate-geometry-equation-of-a-plane)
+
+![](./plane.png)
+
+Thus float4 is the best type to store the plane. First xyz is the normal and w is distance.
+
+In Renderer.swift, you have added this line in draw(in:) below // Water render:
+
+```
+var clipPlane = float4(0, 1, 0, 0.1)
+```
+
+Now you can understand what it is. This plane is pointing towards the positive y axis and located at 0.1 on the y axis.
+
+Maybe you can't understand why this book uses dot product for the clip distance. Let's recap the dot product to understand this.
+
+![](./dot-product.png)
+
+One of the feature of the dot product is projection. From doing dot product between a vertex position and a clip plane, you can know this vertex position is before that plane or after that plane. If a position is located before the plane then the result of dot product is negative. In other case, the result is positive. Now you can easily understand this:
+
+```
+vertex_out.clip_distance[0] = dot(uniforms.modelMatrix * vertex_in.position, uniforms.clipPlane);
+```
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@@ -33,6 +33,7 @@ You can see color images in this book at [here](https://www.raywenderlich.com/bo
  * [Chapter 16: Particle Systems](https://github.com/daemyung/metal-by-tutorials/tree/main/16-particle-systems)
  * [Chapter 18: Rendering with Rays](https://github.com/daemyung/metal-by-tutorials/tree/main/18-rendering-with-rays)
  * [Chapter 19: Advanced Shadows](https://github.com/daemyung/metal-by-tutorials/tree/main/19-shadows)
+ * [Chapter 20: Advanced Lighting](https://github.com/daemyung/metal-by-tutorials/tree/main/20-advanced-lighting)
 
 ## Copyright