draw_surface_tiled_ext(id, x, y, xscale, yscale, col, alpha);
Argument Description id The unique ID value of the surface to draw. x The x coordinate of where to draw the surface. y The y coordinate of where to draw the surface. xscale The horizontal scaling of the surface. yscale The vertical scaling of the surface. h The height of the area the stretched surface will occupy. col The colour with which to blend the surface. alpha The alpha of the surface.
This function will take a surface and then repeatedly tile it across the whole room, starting from the coordinates that you give in the function and with each tile scaled, colour blended and with the alpha that you define (these properties are the same as those used in draw_surface_ext).
draw_surface_tiled_ext(surf, x, y, 2, 2, c_red, 0.5);
This will draw the surface indexed in "surf" at the instances own x and y position, double its stored size and tiled in every direction in the room, as well as blended with the colour red and partially transparent.