From e5c0bba74068d20a7f7b7040c8ea29aad4f50e59 Mon Sep 17 00:00:00 2001
From: daemyung jang <dm86.jang@gmail.com>
Date: Mon, 19 Apr 2021 19:19:02 +0900
Subject: [PATCH] Summerize Chapter 2: 3D Models

---
 02-3d-models/README.md | 19 +++++++++++++++++++
 README.md              |  1 +
 2 files changed, 20 insertions(+)
 create mode 100644 02-3d-models/README.md

diff --git a/02-3d-models/README.md b/02-3d-models/README.md
new file mode 100644
index 0000000..3b712e0
--- /dev/null
+++ b/02-3d-models/README.md
@@ -0,0 +1,19 @@
+# Chapter 2: 3D Models
+
+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.
+
+## Metal coordinate system
+
+The book doesn't mention that The Metal NDC(Normalized Device Coordinate) system is the left-hand coordinate system.
+
+![](https://upload.wikimedia.org/wikipedia/commons/b/b2/3D_Cartesian_Coodinate_Handedness.jpg)
+
+To show the train, this book modified the model file itself. It's not bad but I believe that the model file should be remained to original. Instead of changing y position to -1, we can modify the vertex shader code like below and get the same result.
+
+```
+vertex float4 vertex_main(const VertexIn vertex_in [[ stage_in ]]) {
+  float4 position = vertex_in.position;
+  position.y -= 1.0;  // lower y position by -1
+  return position;
+}
+```
diff --git a/README.md b/README.md
index dd86fe3..5e7f9ed 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,7 @@ You can also download the source code from [here](https://store.raywenderlich.co
 ## Summarize
 
  * [Chapter 1: Hello, Metal!](https://github.com/daemyung/MetalByTutorials/tree/main/01-introduction-to-metal)
+ * [Chapter 2: 3D Models](https://github.com/daemyung/MetalByTutorials/tree/main/02-3d-models)
 
 ## Copyright