Editor/GUILayout - Draw part of a texture

Hi,

i'm trying to achieve a tiled map editor with the unity editor.

My question is about, how should i draw the tiles from my tileset inside the editor?

First, i'm going to expose what i'm currently doing. I go through all the tiles of the tileset and create a new texture for each one of them using GetPixels and SetPixels methods from Texture.

         for (var x = 0; x < TilesetWidth; x++)
         {
             _tiles[x] = new TileSetTile[TilesetHeight];
             for (var y = 0; y < TilesetHeight; y++)
             {
                 var pixels = _tilesetSprite.texture.GetPixels(x * TileSize, ((TilesetHeight - 1) - y) * TileSize, TileSize, TileSize);
 
                 var tileTexture = new Texture2D(TileSize, TileSize);
 
                 tileTexture.SetPixels(pixels);
                 tileTexture.Apply();
 
                 _tiles[x][y] = ...;
             }
         }

And then i use those textures with GUI Buttons to let the user select a tile.

It works, but i feel like it's a really naive way of achieving this. I tried this approach with quite big tileset, with like 1000+ tiles, and... it's slow.

So now i'm wondering, how could i do the same without having to recreate a new Texture2D for each tiles? I have heard of Graphics.DrawTexture but i does not seems to be really convinient as i'd like to display textures inside a GUI Layout.

Can i draw part of a texture in a efficient way inside gui code and keep the GUI Layout system?

Thanks.