Rotating Item Model Baked Quads

[poopoodice]

Hey, I'm now trying to add an item model's quads in another item model's IBakedModel#getQuads. In order to do the dynamic part I need to be able to rotate the vertexes, which I'm not sure how to start with. Any information is appreciated : )

Edited January 13, 2021 by poopoodice

[UguDango]

I have literally done this a few hours ago. Here's what to do.
There's a bit of linear algebra involved, so make sure to look that up. Check out 3Blue1Brown's videos. Especially the ones on 3d. They're a 10-minute watch away.

After that, you have two steps to take into consideration:

1. Rotation, which is a simple linear transform (this should be represented by a 3x3 matrix).
2. Displacement, which is an "offset" so-to-speak which you must apply to your vectors, to make up displaced quads. This is necessary because rotating quads using this method will rotate them around the 0 axis of the block (be it in the direction of x, y, or z. It depends on what you need)

Here's a pic of how I messed up the displacement, so you can understand why it's necessary:

The transparent-blueish spots are where the block is, and as you can see the quads are displaced incorrectly. This was however easily fixed once I went over the maths one more time.

I don't think the mojang Vector3d has a transform function, you'll need to write that yourself. But here's my take on it, so it's easier for you:
 

// The CustomVector3D class extends mojang's Vector3d, so the class fields x, y, z are available

public CustomVector3D linearTransform(double[][] mat) {
        if (mat.length != 3
           || mat[0].length != 3
           || mat[1].length != 3
           || mat[2].length != 3) {
            throw new IllegalArgumentException("Transformation matrix needs to be 3x3x3 in size.");
        }
        double xx = mat[0][0] * this.x + mat[0][1] * this.y + mat[0][2] * this.z;
        double yy = mat[1][0] * this.x + mat[1][1] * this.y + mat[1][2] * this.z;
        double zz = mat[2][0] * this.x + mat[2][1] * this.y + mat[2][2] * this.z;
        return new CustomVector3D(xx, yy, zz);
    }

There are some rotation methods, but I haven't taken a good look at them because I feel more comfortable (at the moment) with doing my own maths.
If you have any questions, please let me know.

[poopoodice]

Hey! Thanks for the reply.

I'm pretty much figured out how to rotate them, but another question has appeared just like what you've said: displacement.

Given the quad I'm not sure where can I get the pivot point, although I can manually type the numbers in but I would like them to be more "automatic", is it possible?

Thanks.

 

Edit: Also there is a helper class provided by Forge called QuadTransformer.

Edited January 15, 2021 by poopoodice

[poopoodice]

On 1/14/2021 at 12:18 PM, UguDango said:

I don't think the mojang Vector3d has a transform function, you'll need to write that yourself.

Maybe not in Vector3d, but there's one in Vector3f