Utility for drawing Unity objects without instantiation

BlockEditorUtil.cs

using UnityEngine;

public class BlockEditorUtil {
    public static void DrawGameObjectHierarchy(
        GameObject obj,
        Vector3 trans,
        Quaternion rot,
        Vector3 scale,
        Material overrideMat
    ) {
        trans += rot * scale.Mul(obj.transform.localPosition);
        rot *= obj.transform.localRotation;
        scale = scale.Mul(obj.transform.localScale);

        DrawGameObjectMesh(obj, trans, rot, scale, overrideMat);

        foreach (Transform child in obj.transform) {
            DrawGameObjectHierarchy(
                child.gameObject,
                trans,
                rot,
                scale,
                overrideMat
            );
        }
    }

    private static void DrawGameObjectMesh(
        GameObject obj,
        Vector3 trans,
        Quaternion rot,
        Vector3 scale,
        Material overrideMat
    ) {
        Mesh mesh;
        Material mat;

        if (obj.TryGetComponent<SkinnedMeshRenderer>(out var smr)) {
            mesh = smr.sharedMesh;
            mat = overrideMat != null ? overrideMat : smr.sharedMaterial;
        } else {
            var filter = obj.GetComponent<MeshFilter>();
            if (filter == null) {
                return;
            }

            mesh = filter.sharedMesh;
            mat = overrideMat != null ? overrideMat : obj.GetComponent<Renderer>().sharedMaterial;
        }

        var matrix = Matrix4x4.TRS(trans, rot, scale);
        Graphics.DrawMesh(mesh, matrix, mat, obj.layer);
    }
}