An in-depth look at why we normalize vectors, connecting game movement logic with Blender's "Apply Scale." Learn why separating direction from magnitude is crucial for consistent physics and lighting.
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When studying Three.js, you often see .normalize() attached to vectors almost like a ritual. Most tutorials just say "it's useful" and move on, but that only made me more curious.
Why turn a perfectly fine vector into length 1? When is it absolutely necessary, and when can we skip it?
Thinking back, this wasn't a entirely new concept. I use Blender frequently, and I've always been told to "Apply Scale" after resizing an object. The reason was always "because things might break later," but I never truly understood why—I just did it out of habit.
Digging into Three.js normalization, I started to see that the Blender habit was actually solving the same problem in a different way.
Normalization is the process of keeping the direction while setting the length to exactly 1.
- Discard "How far it goes"
- Keep "Which direction it points"
Therefore, a normalized vector is usually used for:
They all share a common trait: Direction is more important than magnitude.
Think of a grid game like Chess or older Pokemon. These worlds aren't continuous spaces.
Mathematically, a diagonal move is √2 ≈ 1.41, but in game rules, it's just "one move."
📌 What matters is the rule, not the exact distance value. Thus, the "diagonal is faster" problem never arises.
The space handled in Three.js is completely different:
(x, y, z)If you don't normalize here, problems appear immediately.
Input W + D → (1, 1). The length of this vector is √2 ≈ 1.41.
This means in the same frame:
This isn't just a feeling of speed; the actual position value moves further.
In free-movement games, we follow this flow:
| Movement | Input Vector | Actual Length | After Normalization |
|---|---|---|---|
| Right | (1, 0) | 1.0 | 1.0 |
| Up | (0, 1) | 1.0 | 1.0 |
| Diagonal | (1, 1) | 1.41 | 1.0 |
👀 Visually, you go diagonal.
📐 Mathematically, you move the same distance.
This is where Blender connects. Normal Vectors in Blender represent the "direction of a face" for lighting calculations. These normals are always assumed to have a length of 1.
If you scale an object and don't Apply Scale:
Lighting is usually calculated using the Dot Product.
0 ~ 1 (The expected brightness).📉 This causes:
👉 Apply Scale is essentially saying: "Reset these vectors back to length 1."
.normalize() mutates the original vector.
If you need to keep the original position or magnitude, clone it first.
const direction =
You don't need it everywhere.
But the moment you think of "Direction," you almost always use it.
If you use OrbitControls, it's handled internally. But if you make your own:
mesh.position.x += 1; (Fixed coordinate move).Without normalization, the speed would vary depending on the distance.
A Ray is a Direction Vector.
raycaster.setFromCamera(mouse, camera);
Raycasters assume the direction vector is normalized. If it isn't, click detection might happen at wrong positions or affect performance.
If you use built-in materials, Three.js handles it. But you must intervene when:
vec3 lightDir = normalize(lightPos - vPos); is mandatory. Skipping it causes light to "explode" or flicker.Normalization isn't just a math trick. It is:
Now, the reason to use .normalize() is crystal clear.
.normalize() → (0.7, 0.7).const v = new THREE.Vector3(3, 4, 0);
v.normalize(); // v is now (0.6, 0.8, 0)
const direction = target.clone().sub(mesh.position).normalize();
mesh.position.add(direction.multiplyScalar(speed));
mesh.scale.set(10, 1, 1);.