Rotate UV of Object by 90 Degrees

Scripting
1

I want a generic function that will rotate the uv coordinates of any mesh 90 degrees clockwise or counterclockwise around the positive y axis. How would that be done without using a shader – I only need to do the rotation once at the start of the game.

2
  • Add a script to the object that needs rotated uv
  • In the Start function, find the MeshFilter and obtain its mesh
  • Get the uv array from mesh.uv
  • Rotate every vertex in the array by multiplying it with the Quaternion corresponding to your rotation angle
  • Assign the array back to mesh.uv

If this needs to be done for a lot of large meshes, it may be worth putting this functionality in an editor script instead. That may save you some time loading the level with the meshes in it.

3

Thanks. Two follow up questions:

  1. Can you provide an example of the quaternion multiplication.
  2. How do I use editor scripts? Ideally I’d like to make the rotation happen in-editor for certain objects, so as you said, in-game resources aren’t being used.
4

I meant it quite literally:

Vector3 rotated = Quaternion.Euler(0,0,-90) * Vector3.up;

An AssetPostProcessor is probably the best place for this. Unfortunately, (as far as I know) the only way to communicate with a post processor it is through the file name of the processed asset. So, models that need rotated uv will need a specific string in their name to be able to separate them from other models that don’t need rotated uv:

5

Hey Sorry to dig ths old thread up but I was trying to do the same thing and I’m really stuck,
Here’s my script :

var DeckMesh : Mesh;

function Update () {
	var RotatedUVs : Vector2[] = DeckMesh.uv;//Store the existing UV's
	
	Vector3rotated = Quaternion.Euler(0,0,-90) * Vector3.up;
	
    for (var i = 0 ; i < RotatedUVs.Length; i++){//Go through the array
        RotatedUVs[i] += Vector2(.05,.09);//i can move them okay...
        print (i);
    }
	
	DeckMesh.uv = RotatedUVs;//re-apply the adjusted uvs
}

I can move them okay but I don’t understand how I could get them to rotate?
Thanks
Pete

6

Try something like this:

var DeckMesh : Mesh;

function Update () {
	var RotatedUVs : Vector2[] = DeckMesh.uv;//Store the existing UV's
	
	
    for (var i = 0 ; i < RotatedUVs.Length; i++){//Go through the array
        RotatedUVs[i] += Vector2(.05,.09);//i can move them okay...
	var rot = Quaternion.Euler(0,0,-90 * Time.deltaTime);
        RotatedUVs[i] = rot * RotatedUVs[i];
    }
	
	DeckMesh.uv = RotatedUVs;//re-apply the adjusted uvs
}

This will rotate the uv by 90 degrees every second. I would also highly recommend multiplying your movement vector with Time.deltaTime, as your current animation speed depends on the framerate.

7

Thanks tomvds, That works! One thing though, it seems to be moving both uv and uv2? Is there a way to isolate them?

8

It only manipulates uv. To change uv2, you would have to apply the same code to DeckMesh.uv2. Are you sure your shader uses uv2 and not just uv multiple times?

9

hmm, weird I’ll have to have a look over my shader and see what’s going on there.
Thanks for the help!

10

I wonder if I could use this for my game.

I’ve big grid mesh for top down 2D game, where each grid square of the mesh is mapped to texture on sprite sheet.

I need to be able to rotate a texture on any given square, would approach posted on this thread work?

For example to set desired texture from sprite sheet I use this code:

int uvIndex = TileIndex * 4;

uvs[uvIndex + 0] = new Vector2(u, v);
uvs[uvIndex + 1] = new Vector2(u+0.0625f, v);
uvs[uvIndex + 2] = new Vector2(u, v+0.0625f);
uvs[uvIndex + 3] = new Vector2(u+0.0625f, v+0.0625f);

So can use same code to rotate texture on part of mesh?

11

I don’t see any reason why it wouldn’t work. Note that if you need rotations that are not a multiple of 90 degrees, it may look odd as pixels of neighboring sprites from the sprite sheet will fall into your tile.

12

Thank you. I solved this issue by simply shifting uv’s around, for example to make 90 degree rotation left I set uv1 to uv2, uv2 to uv3, uv3 to uv4 and so on, works perfectly!

13

Here’s the code I use to rotate a mesh’s UVs around the center point:

    public static void RotateUVs(this Vector2[] uvs, float rotationRadians)
    {
        float rotMatrix00 = Mathf.Cos(rotationRadians);
        float rotMatrix01 = -Mathf.Sin(rotationRadians);
        float rotMatrix10 = Mathf.Sin(rotationRadians);
        float rotMatrix11 = Mathf.Cos(rotationRadians);

        Vector2 halfVector = new Vector2(0.5f, 0.5f);

        for (int j = 0; j < uvs.Length; j++)
        {
            // Switch coordinates to be relative to center of the plane
            uvs[j] = uvs[j] - halfVector;
            // Apply the rotation matrix
            float u = rotMatrix00 * uvs[j].x + rotMatrix01 * uvs[j].y;
            float v = rotMatrix10 * uvs[j].x + rotMatrix11 * uvs[j].y;
            uvs[j].x = u;
            uvs[j].y = v;
            // Switch back coordinates to be relative to edge
            uvs[j] = uvs[j] + halfVector;
        }
    }
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