for (var yy = 0; yy < height*2; yy++) {
    for (var xx = 0; xx < width*2; xx++) {
        if (grid[# xx div 2, yy div 2] == FLOOR) {
            // Get the tile's x and y
            var tx = xx*tw;
            var ty = yy*th;

            var right = grid[# (xx+1) div 2, yy div 2] != FLOOR;
            var left = grid[# (xx-1) div 2, yy div 2] != FLOOR;
            var top = grid[# xx div 2, (yy-1) div 2] != FLOOR;
            var bottom = grid[# xx div 2, (yy+1) div 2] != FLOOR;

            var top_right = grid[# (xx+1) div 2, (yy-1) div 2] != FLOOR;
            var top_left = grid[# (xx-1) div 2, (yy-1) div 2] != FLOOR;
            var bottom_right = grid[# (xx+1) div 2, (yy+1) div 2] != FLOOR;
            var bottom_left = grid[# (xx-1) div 2, (yy+1) div 2] != FLOOR;

            if (right) {
                if (bottom) {
                    tile_add(bg_walltiles, tw*4, th*1, tw, th, tx+tw, ty, -ty);
                } else if (top) {
                    if (top_right) {
                        tile_add(bg_walltiles, tw*4, th*0, tw, th, tx+tw, ty-th, -ty);
                    } else {
                        tile_add(bg_walltiles, tw*3, th*0, tw, th, tx, ty-th, -ty);
                    }
                    tile_add(bg_walltiles, tw*0, th*1, tw, th, tx+tw, ty, -ty);
                } else {
                    tile_add(bg_walltiles, tw*0, th*1, tw, th, tx+tw, ty, -ty);
                }
            }

            if (left) {
                if (bottom) {
                    tile_add(bg_walltiles, tw*3, th*1, tw, th, tx-tw, ty, -ty);
                } else if (top) {
                    if (top_left) {
                        tile_add(bg_walltiles, tw*3, th*0, tw, th, tx-tw, ty-th, -ty);
                    } else {
                        tile_add(bg_walltiles, tw*4, th*0, tw, th, tx, ty-th, -ty);
                    }
                    tile_add(bg_walltiles, tw*2, th*1, tw, th, tx-tw, ty, -ty);
                } else {
                    tile_add(bg_walltiles, tw*2, th*1, tw, th, tx-tw, ty, -ty);
                }
            }

            if (top) {
                if (!top_right) {
                    tile_add(bg_walltiles, tw*2, th*2, tw, th, tx, ty-th, -ty);
                } else if (!top_left) {
                    tile_add(bg_walltiles, tw*0, th*2, tw, th, tx, ty-th, -ty);
                } else {
                    tile_add(bg_walltiles, tw*1, th*2, tw, th, tx, ty-th, -ty);
                }
            }

            if (bottom) {
                if (!bottom_right) {
                    tile_add(bg_walltiles, tw*2, th*0, tw, th, tx, ty, -ty-tw);
                } else if (!bottom_left) {
                    tile_add(bg_walltiles, tw*0, th*0, tw, th, tx, ty, -ty-tw);
                } else {
                    tile_add(bg_walltiles, tw*1, th*0, tw, th, tx, ty, -ty-tw);
                }
            }
        }
    }
}