SoftBody3D: cloth, pins and deformation

using Reckfell;

public partial class SoftBodyLab3D : Entity3D
{
    public const int Columns = 9;
    public const int Rows = 9;
    public SoftBody3D Cloth { get; private set; } = null!;
    public bool PinsReady { get; private set; }
    public override void _Ready()
    {
        var vertices = new Vector3[Columns * Rows];
        var normals = new Vector3[vertices.Length];
        for (int row = 0; row < Rows; row++)
            for (int col = 0; col < Columns; col++)
            {
                int i = row * Columns + col;
                vertices[i] = new Vector3(-1 + 2f * col / (Columns - 1), 3, 2f * row / (Rows - 1));
                normals[i] = Vector3.Up;
            }
        var indices = new int[(Columns - 1) * (Rows - 1) * 6]; int index = 0;
        for (int row = 0; row < Rows - 1; row++)
            for (int col = 0; col < Columns - 1; col++)
            {
                int a = row * Columns + col, b = a + 1, c = a + Columns, d = c + 1;
                foreach (int point in new[] { a, c, b, b, c, d }) indices[index++] = point;
            }
        var arrays = new Reckfell.Collections.Array(); arrays.Resize((int)Mesh.ArrayType.Max);
        arrays[(int)Mesh.ArrayType.Vertex] = vertices; arrays[(int)Mesh.ArrayType.Normal] = normals; arrays[(int)Mesh.ArrayType.Index] = indices;
        var mesh = new ArrayMesh(); mesh.AddSurfaceFromArrays(Mesh.PrimitiveType.Triangles, arrays, flags: Mesh.ArrayFormat.FlagUseDynamicUpdate);
        Cloth = new SoftBody3D { Name = "Cloth", Mesh = mesh, TotalMass = 1, LinearStiffness = .5f,
            SimulationPrecision = 5, PressureCoefficient = 0, CollisionLayer = 4, CollisionMask = 1,
            MaterialOverride = new StandardMaterial3D { AlbedoColor = new Color(.25f,.45f,1), ShadingMode = BaseMaterial3D.ShadingModeEnum.Unshaded, CullMode = BaseMaterial3D.CullModeEnum.Disabled } };
        AddChild(Cloth);
        var floor = new StaticBody3D { Position = new Vector3(0,-.2f,0), CollisionLayer = 1, CollisionMask = 0 };
        floor.AddChild(new CollisionShape3D { Shape = new BoxShape3D { Size = new Vector3(8,.4f,6) } });
        floor.AddChild(new MeshInstance3D { Mesh = new BoxMesh { Size = new Vector3(8,.4f,6) }, MaterialOverride =
            new StandardMaterial3D { AlbedoColor = new Color(.55f,.55f,.6f), ShadingMode = BaseMaterial3D.ShadingModeEnum.Unshaded } }); AddChild(floor);
        var camera = new Camera3D { Position = new Vector3(4,3,6), Current = true }; AddChild(camera); camera.LookAt(ToGlobal(new Vector3(0,1.5f,0)));
    }
    public override void _PhysicsProcess(double delta)
    {
        if (PinsReady || Cloth.PointCount != Columns * Rows) return;
        for (int col = 0; col < Columns; col++) Cloth.SetPointPinned(col, true, new EntityPath(""), -1);
        PinsReady = true;
    }
    public void ReleaseTop()
    {
        if (!PinsReady) return;
        for (int col = 0; col < Columns; col++) Cloth.SetPointPinned(col, false, new EntityPath(""), -1);
    }
    public override void _UnhandledKeyInput(InputEvent @event)
    {
        if (@event is InputEventKey { Pressed: true, Echo: false } key)
        {
            if (key.PhysicalKeycode == Key.Space && PinsReady) Cloth.ApplyCentralImpulse(new Vector3(0,0,1));
            if (key.PhysicalKeycode == Key.R) ReleaseTop();
        }
    }
}