-Tile300 (Scenery Custom Block) -Tile15 (Solid Custom Block/Inviso Block) -Background N°11 (Well it's not a tile, but it's a customizable BG)
Well let's get started: First of all, Sorry for my bad english, second, you need paint.net ofc for the tile editing, so let's move on into the requirements:
-The BG must be 320x240 -The Tiles well, it's recommended to be 20x20 but you can use those resolution combinations here: (20x20-20x40-20x60-20x80-20x100, same thing for 40x, 60, 80 and 100) -They must be in the .png format
P.S: The background MUST be cutoff-free.
After editing your tile/bg with those requirements, you'll export them into the "graphics" folder of SMF 5.0.0.3, with the name of the tile you want. (Ex: Tile300 = tile300.png Tile15 = tile15.png Background 11 = bg11.png), run the game and test it.
Now the code-editing part: The Soliding of the Tile15 that the resolution is GREATER than 20x20.
First of all you'll grab the Tile15 that the resolution is higher than 20x20 on the level area, and will fill the non-solid areas of the tile with a random solid tile. (Ex: Tile178) , and with code-editing you'll replace the random tiles WITH Tile6 (Inviso Tile) and test it. (P.S: You can also do this with the Tile300).