Godot procedural mesh generation

Question

I am strugling with godot 4.1 procedural mesh generation. Here is the code (sorry for the mess, it is still experiment):

using Godot;
using Godot.Collections;
using System;
using System.Collections.Generic;

[GlobalClass]
public partial class ChunkMesh : ArrayMesh
{
    private Vector3 downLeft = Vector3.Left + Vector3.Down;
    private Vector3 downRight = Vector3.Right + Vector3.Down;
    private Vector3 upLeft = Vector3.Up + Vector3.Left;
    private Vector3 upRight = Vector3.Up + Vector3.Right;
    private Godot.Collections.Array arrays = new Godot.Collections.Array();
    private List<Vector3> vertex = new List<Vector3>();
    private List<Vector3> normal = new List<Vector3>();
    private List<Color> color = new List<Color>();
    private List<int> indices = new List<int>();

    private void Begin()
    {
        ClearSurfaces();
        vertex.Clear();
        normal.Clear();
        color.Clear();
        indices.Clear();
    }

    private void End()
    {
        arrays.Resize((int)ArrayType.Max);
        arrays[(int)ArrayType.Vertex] = vertex.ToArray();
        arrays[(int)ArrayType.Normal] = normal.ToArray();
        arrays[(int)ArrayType.Color] = color.ToArray();
        arrays[(int)ArrayType.Index] = indices.ToArray();
        AddSurfaceFromArrays(PrimitiveType.Triangles, arrays);
    }

    private Vector3 Rotate(Vector3 toRotate, Vector3 axis, float angle)
    {
        if (axis.Length() == 0)
            return toRotate;
        return toRotate.Rotated(axis, angle);
    }

    private void DrawPoint(Vector3 position, Vector3 direction, Color color)
    {
        this.normal.Add(direction);
        this.color.Add(color);
        this.vertex.Add(position);
    }

    public void DrawQuad(Vector3 position, Vector3 direction, float scale, Color color)
    {
        direction = direction.Normalized();
        Vector3 dirDiff = Vector3.Back - direction;
        Vector3 rotateAxis = Vector3.Back.Cross(dirDiff).Normalized();
        float angle = Vector3.Back.SignedAngleTo(dirDiff, rotateAxis);
        scale /= 2;
        Begin();
        DrawPoint(position + Rotate(downLeft * scale, rotateAxis, angle), direction, color);
        DrawPoint(position + Rotate(upLeft * scale, rotateAxis, angle), direction, color);
        DrawPoint(position + Rotate(upRight * scale, rotateAxis, angle), direction, color);
        DrawPoint(position + Rotate(downRight * scale, rotateAxis, angle), direction, color);
        indices.Add(0);
        indices.Add(1);
        indices.Add(2);
        indices.Add(2);
        indices.Add(3);
        indices.Add(0);
        End();
    }
}

using Godot;
using System;

[GlobalClass]
public partial class Chunk : MeshInstance3D
{
    // Called when the node enters the scene tree for the first time.
    public override void _Ready()
    {

    }

    // Called every frame. 'delta' is the elapsed time since the previous frame.
    public override void _Process(double delta)
    {
        float scale = Time.GetTicksMsec() / 1000f % (Mathf.Pi * 2);
        ((ChunkMesh)Mesh).DrawQuad(Vector3.Zero, Vector3.Back.Rotated(Vector3.Up, scale), 1.0F, new Color("red"));
    }
}

I was trying ImmediateMesh, now I am trying ArrayMesh. Whatever I do, there is no mesh displayed, even when I choose wireframe view in the editor - there is nothing. What am I doing wrong?

Edit 1: I've figured out, that if I save the mesh like this:

ResourceSaver.Save(Mesh, "res://quad.tres", ResourceSaver.SaverFlags.Compress);

That mesh is proper, so there must be a problem with assigning / commiting / displaying ?

Edit 2: I run almost similar code in godot 3.5 - it works, so... probably it is a bug, I've reported it here: https://github.com/godotengine/godot/issues/83958

Answer 1

Your code is fine, I tweaked it and got it working in 4.1.2, Adjust your _Process method as follows.

public override void _Process(double delta)
{
    float scale = Time.GetTicksMsec() / 1000f % (Mathf.Pi * 2);
    var chunkMesh = new ChunkMesh();
    chunkMesh.DrawQuad(Vector3.Zero, Vector3.Back.Rotated(Vector3.Up, scale), 1.0F, new Color("red"));
    Mesh = chunkMesh;
}