Matrix3d.java

public class Matrix3d {
    double[] values;

    Matrix3d(double[] values) {
        this.values = values;
    }

    Matrix3d multiply(Matrix3d other) {
        double[] result = new double[9];
        for (int row=0; row < 3; row++) {
            for (int col=0; col < 3; col++) {
                for (int i = 0; i < 3; i++) {
                    result[row * 3 + col] +=  this.values[row*3+i] * other.values[i*3+col];
                }
            }
        }

        return new Matrix3d(result);

    }

    Vertex transform(Vertex in) {
        return new Vertex( 
            in.x * values[0] + in.y * values[3] + in.z * values[6],
            in.x * values[1] + in.y * values[4] + in.z * values[7],
            in.x * values[2] + in.y * values[5] + in.z * values[8]
        );
    }
}