While making a top-down map for my game, I needed to arrange some of its parts to fit better together, which required rotating some sections. Since PICO-8 does not provide a way to rotate a map selection, I wrote a simple utility function to do that.

This function rotates a square section of the map clockwise.
MX and MY are the map X and Y coordinates of the upper left corner, and MS is the length of the square side - 1 (e.g. to rotate an 8x8 square, set MS=7)

Notes:

• Make sure that you do not modify the map in any way before you call the rotate function, or the in-memory changes will be written to the cart
• Uncomment the second CSTORE (or edit the to edit the lower portion of the map
• This function is not optimized and is not intended for frequent use (unless you are making some gravity-based platformer, I suppose...)

-- rotate a square section 
-- of a map clockwise
function rotate_map(mx,my,ms)
	-- read tiles
	local tiles={}
	for x=0,ms do
		tiles[x]={}
		for y=0,ms do
			tiles[x][y]=
				mget(mx+x,my+y)
		end
	end
	-- write tiles
	for x=0,ms do
		for y=0,ms do
			local tx=y
			local ty=mx+ms-x
			mset(mx+x,my+y,tiles[tx][ty])
		end
	end
	cstore(0x2000,0x2000,0x1000)
	-- to edit extended map, uncomment
	--cstore(0x1000,0x1000,0x1000)
end