"the next file in the folder"

Platypus · March 2013

Hi, guys.

In my Gideros project, I made a folder called "images" and filled it with about 264 images. I then clicked "sort", so they are arranged in numerical order (of filename).

Their names are of the following style (but might change):

0000.png
0010.png
0020.png
0024.png
0029.png
0030.png
.
.
2700.png

All of them are images that fill the entire screen. The app is an e-book. When it starts, it will display 0000.png (the book's cover).

What is the best way to write the following three functions?

[Load the next image from the "/images/" folder into memory.]
[Now, display it and load the next image from the "/images/" folder into memory.]
[Display the previous image (which is, hopefully, still in memory) again.]

Thanks very much.
Platypus

Mells · March 2013

@Platypus
Hello and welcome, have you checked The E-book Template?
That would cut your dev time, the page management work is already done so you can focus on your art + texts.

Scouser · March 2013

Just the fact that you say the naming convention may change makes this a little problematic. You could try something like this to read the directory into a table and then select the filenames by iterating through the table,

Platypus · March 2013

Dear @Mells and @Scouser,

Thanks, guys. Yeah, I have been analysing both of those (both the e-book and that webpage) during the past few days (plus numerous Gideros resources, posts on this forum and many other Lua resources), but I cannot decide upon (Well,.. I cannot even recognise) the simplest solution to use.

In that e-book template (which is absolutely wonderful), each page is a separate scene and a separate Lua file, which is probably necessary for an interactive e-book.

Mine has hundreds of pages, but it is not interactive at all. It is just a folder full of screen-sized images.

I need to be able to reuse the code for all future books I release, and I always need to be able to insert pages easily. That's why I name them in multiples of ten.
e.g. It's easy to insert "0725.png" between the following files:
.
.
0710.png
0720.png
0730.png
.
.

Isn't there some kind of one-line solution?
(Attention Beginners - The following is not valid code.)
Some kind of code like:

current = 0720

Function
LoadFile "images/(>current).png"
current = (>current)
End

...or something equally short and sweet? I really hope there is. I want the computer to do the computing.

Platypus · March 2013

Could any of the following commands be applied in this case?

loadfile?
dofile?
read?
readfile?
require?
io.open?
io.read?
io.getElements?

How about this:

(From @atilim's code on
http://www.giderosmobile.com/forum/discussion/comment/90#Comment_90 )

local f = io.open("images/", "....(Something?)....")
local t = f:read("*all")
f:close()

?

ar2rsawseen · March 2013

Maybe I don't really understand the issue here, but would it not be easier to create for example a global variable with current image, and load each image in the separate scene, like this:
Somewhere in main lua

curImage = 0
maxImage = 9000
function imageFormat(num)
    if num < 10 then
        return "000"..num
    elseif num < 100 then
        return "00"..num
    elseif num < 1000 then
        return "0"..num
    end
    return num
end

And then in scene

scene = Core.class(Sprite)
 
--in the init
function scene:init()
    --load current image
    local bitmap = Bitmap.new(Texture.new("images/"..imageFormat(curImage)..".png"))
end
 
--provide methods to switch images
function scene:next()
    if(curImage < maxImage)
        curImage = curImage + 1
    end
end
 
function scene:prev()
    if(curImage > 0)
        curImage = curImage - 1
    end
end

Well I used scene manager, but this approach can be firstly be used without it, secondly used in combination of pre-loading next and previous image

I don't think there is a need to store all of them in memory, it might not be feasible.

Scouser · March 2013

@Platypus: Somewhere along the lines, you are going to need a table containing the filenames (or at least the numeric part of the filenames) as they are not sequential so there is no easy way of knowing what the next page is going to be. As you said yourself, you may insert an image between 0160 & 0170 which would become 0165. How do you expect the software to know there is a new page after 0160 unless you specifically tell it so.

That is why I suggested the directory method as it wouldn't matter how many images you inserted, the software would automatically find it during the directory search.

ar2rsawseen · March 2013

oh, not sequencial, thats what I missed

ar2rsawseen · March 2013

But then you can use Lua File System plugin:

require"lfs"
 
function listdir (path)
	for file in lfs.dir(path) do
		if file ~= "." and file ~= ".." then
			local f = path..'/'..file
			print (f)
		end
	end
end
 
listdir (".")

Scouser · March 2013

Something similar to what @ar2rsawseen wrote:

require"lfs"
 
function getdir (path)
	local pages={}
	for file in lfs.dir(path) do
		if file ~= "." and file ~= ".." then
			if string.sub(file,-4) == ".png" then pages[#pages+1] = file end
		end
	end
	return pages
end
 
pages = getdir ("pages")

should return a list of all the .png files in a directory.

Platypus · March 2013

Fantastic stuff, guys! Thank you very much for being so helpful. I sincerely appreciate it. I will study your suggested methods.

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