blender: add a post to pop up a letter by letter animation

content/docs/blender.md

@@ -6,7 +6,9 @@ draft: false
 ---
 
 # Table of contents
-- [Gradient color](/posts/2023/12/16/blender-animate-a-gradient-material/)
+- [Gradient color of a text](/posts/2023/12/16/blender-animate-a-gradient-material/)
+- Animation examples of text
+    - [Fade in: pop up each letter of a text](/posts/2023/12/17/blender-scale-text-by-each-letter/)
 
 
 # Old contents

content/posts/2023-12-16-blender-animate-gradient-material.md

@@ -4,7 +4,7 @@ date: 2023-12-16T15:17:29-08:00
 draft: false
 tags:
   - blender
-  - blender_4.0
+  - blender 4.0
 ---
 
 This post was written using Blender 4.0.

content/posts/2023-12-17-blender-scale-text-by-each-letter.md

@@ -0,0 +1,96 @@
+---
+title: "Blender Scale Text by Each Letter"
+date: 2023-12-17
+draft: false
+tags:
+  - blender
+  - blender 4.0
+---
+
+This was written using Blender 4.0 by a Blender novice.
+
+The animation in this post looks like next.
+
+<video src="/posts/2023/2023-12-17-blender-scale-text-by-each-letter/videos/step4.mp4" width="100%" height="auto" controls></video>
+
+Except step 4, I referred to [this stackexchange answer](https://blender.stackexchange.com/questions/277352/scale-individual-letters-separately-from-string-to-curves-geometry-nodes-in-blen).
+
+## Step 1: Scale an entire text on Geometry Nodes
+
+![](/posts/2023/2023-12-17-blender-scale-text-by-each-letter/images/step1.png)
+
+1. Add a **Instances > Scale Instances** node and connect between **Group Input** and **Group Output**
+    - Set **Y** of **Scale** to 2.0 and make sure the text scales
+1. Add a **Utilities > Text > String to Curves** node and set the **String** field on the node
+    - Connect from **Curve Instances** of **String to Curves** to **Instances** of **Scale Instances** instead of **Group Input**.
+1. Add a **Curve > Operations > Fill Curve** and put it between **String to Curves** and **Scale Instances**
+
+
+Note that I couldn't figure out how to use the text of its mesh from the **Geometry Input** node for following animation steps correctly.
+
+
+## Step 2: Animate texts by time frame
+
+<video src="/posts/2023/2023-12-17-blender-scale-text-by-each-letter/videos/step2.mp4" width="100%" height="auto" controls></video>
+
+1. Add a **Input > Scene > Scene Time** node
+1. Add a **Utilities > Math > Map Range** node and on the node,
+    - Connect the **Frame** of the **Scene Time** node to the **Value**
+    - Connect the **Result** to the **Scale** of the **Scale Instances** node
+    - Update the **From Max** and **To Max** values for testing. For example,
+        - **From Max**: Set 10 so that the text gets the biggest size at 10 keyframe
+        - **To Max**: The max scale size of the text
+1. This is optional for an animation to change pop up a text from the bottom center instaed of bottom left of each letter. On the **String to Curve** node,
+    - Updbate **Pivot Point** to **Bottom Center** 
+    - Connect the output of **Pivot Point** to **Center** of **Scale Instance**
+
+What Map Range does is to convert the value from `(From Min, From Max)` to `(To Min, To Max)` [^1].
+
+[^1]: [Blender 4.0 Manual: Map Range node](https://docs.blender.org/manual/en/4.0/modeling/geometry_nodes/utilities/math/map_range.html)
+
+
+## Step 3: Animate texts by each letter
+
+<video src="/posts/2023/2023-12-17-blender-scale-text-by-each-letter/videos/step3.mp4" width="100%" height="auto" controls></video>
+
+Now use the **Index**[^2] node to change the scale for each letter via **Map Range** node.
+
+[^2]: [Blender 4.0 Manual: Index node](https://docs.blender.org/manual/en/4.0/modeling/geometry_nodes/geometry/read/input_index.html)
+
+1. Add a **Geometry > Read > Index** node
+1. Add a **Utilities > Math > Math** node, which is used for the interval frames of each letter, and on the node
+    - Update the function to **Multiply**
+    - Connect the output from the **Index** node to one of **Value**
+    - Connect the output of **Value** on this node to the **From Min** of the **Map Range** node
+    - Set another **Value** to an arbitarily number like 10 for the interval
+1. Add a **Utilities > Math > Math** node, which is used for how long it takes to scale each letter, and on the node,
+    - Update the function to **Add**
+    - Connect the output of **Value** on the **Multiply** node to the one of the **Value** of this node
+    - Connect the output of **Value** on this node to the **From Max** of the **Map Range** node
+    - Set another **Value** to an arbitarily number like 20 for how long takes to animate each letter
+
+## Step 4: Animate texts like soft objects
+
+Animate texts like following squash and stretch principle.
+I couldn't refer to anywhere, so there might be a better way.
+
+<video src="/posts/2023/2023-12-17-blender-scale-text-by-each-letter/videos/step4.mp4" width="100%" height="auto" controls></video>
+
+The logic of this animation looks like next.
+
+- Decide what is the max scale of each letter, let's say `threshold`.
+- Assuming the value of the **Map Range** node is `v_index`,
+    - Set the **To Max** of the **Map Range** node to `2 * (threshold - 1) + 1`, let's say `t_max`
+    - Set the scale
+        - `t_max + 1 - s` if `v_index > threshold`, 
+        - `v_index` otherwise
+
+Note that the speed for a text to be bigger than 1.0 to `threshold`, and from `threshold` to 1.0 is the same.
+
+To change the scale value based on the value by the above formula, I used **Greater Than** and **Mix** nodes by connecting the output of **Greater Than** to **Factor** of **Mix**.
+Other than that, add many **Math** nodes to calculate the above.
+
+
+
+# Reference
+- [Stackexchange answer](https://blender.stackexchange.com/questions/277352/scale-individual-letters-separately-from-string-to-curves-geometry-nodes-in-blen)