Summerize Chapter 13: Instancing & Procedural Generation

13-procedural-generation/README.md

@@ -0,0 +1,40 @@
+# Chapter 13: Instancing & Procedural Generation
+
+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.
+
+## Morphing
+
+Morphing which is explaned by this book isn't the cannonical way of morphing. Morphing is usually a morphable mesh where primitives’ attributes are obtained by adding the original attributes to a weighted sum of targets attributes.
+
+![](./morphing.png)
+
+For instance, the the position of vertices for the primitive at index i are computed in this way:
+
+```
+primitives[i].attributes.POSITION + 
+  weights[0] * primitives[i].targets[0].POSITION +
+  weights[1] * primitives[i].targets[1].POSITION +
+  weights[2] * primitives[i].targets[2].POSITION + ...
+```
+
+Apple's animoji is the most famous example of morphing.
+
+![](./animoji.webp)
+
+## Miscalculation of the world position
+
+In Nature.metal and Houses.metal, the world position is calculated incorrectly, replace:
+
+```
+out.worldPosition = (uniforms.modelMatrix * vertexIn.position
+                        * instance.modelMatrix).xyz;
+```
+
+With:
+
+```
+out.worldPosition = (uniforms.modelMatrix * instance.modelMatrix
+                        * vertexIn.position).xyz;
+```
+
+The result isn't changed because the world position is not used anywhere.

README.md

@@ -27,6 +27,7 @@ You can see color images in this book at [here](https://www.raywenderlich.com/bo
  * [Chapter 10: Fragment Post-Processing](https://github.com/daemyung/metal-by-tutorials/tree/main/10-trees-and-fog)
  * [Chapter 11: Tessellation & Terrains](https://github.com/daemyung/metal-by-tutorials/tree/main/11-tesselation-and-terrains)
  * [Chapter 12: Environment](https://github.com/daemyung/metal-by-tutorials/tree/main/12-environment)
+ * [Chapter 13: Instancing & Procedural Generation](https://github.com/daemyung/metal-by-tutorials/tree/main/13-procedural-generation)
 
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