Usually in 3d drawing you want to ideally have fewer larger textures rather than lots of smaller ones, and make sure you render the same kinds of textures at the same time. So there is less texture swapping going on behind the scenes.
This is not a difficult thing to do as most textures are purely used for models or terrains/structures. So you may have a terrain texture, a structures texture and a couple of player/enemy textures. Then just draw the terrain, the structures and any enemies and the player, only requiring a few texture swaps there, and if you are also using some sort of model instancing for the enemies you can get away with some other improvements there.
Anyway now enter the 2d drawing world, rather than applying a texture and then drawing lots of vertices using it you are giving a texture to each draw command. So I am wondering how XNA handles this behind the scenes.
Take for example a top down 2d game, you have a tileset for the level containing many ground sprites, an enemy sprite sheet which may contain anywhere from 10-20 enemies sprites and animations, then possibly a player/equipment sheet which contains anything for them.
Now in this instance if I were to draw my level which was lets say 64x64 tiles (a tile being an x,y,tileSetIndex), and I have a tileset with 8x8 sprites (lets say 32x32 each):
var tileSetSourceRect = someTilesetEntity.GetSourceRectForIndex(tile.tileSetIndex); mySpriteBatch.Draw(someTilesetEntity.TilesetTexture, tileSetSourceRect , tile.Position, Color.White);
assuming no real optimisations and just looping through every tile would this just retain the tilesetTexture in memory, or is it going to keep removing/adding the texture after every Draw() call? As I do not know how it can manage this unless it keeps some state under the hood between draw calls (maybe thats what Begin/End is for on spriteBatches).
So will I be getting 4096 (64x64 tiles itterated) texture swaps, or will it only do 1 texture swap in this instance?