Multimesh via RenderingServer not showing mesh's material

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1

Godot Version

4.6.1

Question

I'm playing with the RenderingServer to display and update thousands of visual instances at once. In particular I've tried instantiating a multimesh and adding to it a mesh resources that I've created via the editor:

public partial class Server: Node2D
{

const N = 10000;
[Export] Mesh mesh;

Rid rid;
Rid multimesh;

public override _Ready()
{
        rid = RenderingServer.CanvasItemCreate();
        RenderingServer.CanvasItemSetParent(rid, GetCanvasItem());

        multimesh = RenderingServer.MultimeshCreate();
        RenderingServer.MultimeshAllocateData(multimesh, N, RenderingServer.MultimeshTransformFormat.Transform2D);
        RenderingServer.MultimeshSetMesh(multimesh, mesh.GetRid());
        RenderingServer.MultimeshSetVisibleInstances(multimesh, N);
        RenderingServer.CanvasItemAddMultimesh(rid, multimesh);

        for(int i = 0; i < N; i++)
        {
            RenderingServer.MultimeshInstanceSetTransform2D(multimesh, i, Transform2D.Identity.Translated(new Vector2(GD.Randf() * GetViewportRect().Size.X, GD.Randf() * GetViewportRect().Size.Y));
        }

}

}

also in gdscript:

extends Node2D

const N = 10000

@export var mesh : Mesh
var multimesh : RID
var rid : RID

func _ready():
	rid = RenderingServer.canvas_item_create()
	RenderingServer.canvas_item_set_parent(rid, get_canvas_item())

	multimesh = RenderingServer.multimesh_create()
	RenderingServer.multimesh_allocate_data(multimesh, N, RenderingServer.MULTIMESH_TRANSFORM_2D)
	RenderingServer.multimesh_set_visible_instances(multimesh, N)
	RenderingServer.multimesh_set_mesh(multimesh, mesh)

	var t = Transform2D()
	for i in N:
		RenderingServer.multimesh_instance_set_transform_2d(multimesh, i, t.translated(Vector2(randf()*get_viewport_rect().size.x,randf()*get_viewport_rect().size.y)))

	RenderingServer.canvas_item_add_multimesh(rid, multimesh)

The mesh used is a QuadMesh that has a material attached to it, with an Albedo set to a different color than white. However, in both cases at runtime the scene shows all the instances as white squares. I wonder how to properly show the material and, eventual textures added to the mesh. Instantiating a new canvas item for each visual item was easier because I could change their textures directly with RenderingServer.canvas_item_set_texture_rect() (and the performances also looked better so I wonder why would I like to use multimesh over single canvas items ).

2

You need to set the material for the instance. Try instance_geometry_set_material_override()

3

Thank you, I’ve tried adding either:

RenderingServer.instance_geometry_set_material_override(multimesh, mesh.material.get_rid())

or:

RenderingServer.instance_geometry_set_material_override(rid, mesh.material.get_rid())

but none of them worked and the debugger printed

E 0:00:01:721 prova.tscn::GDScript_5iyab:17 @ _ready(): Parameter “instance” is null.
<Sorgente C++>servers/rendering/renderer_scene_cull.cpp:1345 @ instance_geometry_set_material_override()
prova.tscn::GDScript_5iyab:17 @ _ready()

in both cases.

Maybe I did not understand how to use it correctly.

4

Oh, you’re adding a 2d mesh to a canvas item. Then try canvas_item_set_material()