Writing to a binary file format. ACO

[Muzz]

Hi guys!

I need a bit of help.

I have a simple binary file type i need to write out from love2d, http://www.adobe.com/devnet-apps/photos ... 7411_20528 ctrl+f and do a search for aco, and you will get to the fomat spec.

It's a super simple spec, but i'm having a few issues. On the irc i've been told to get the correct data types i can use ffi, which i've done.

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  	local ffi = require("ffi")

	ffi.cdef[[
	typedef struct {
	    double version;
	    double colcount;
	} header;

	typedef struct {
		double colourid;
		unsigned short int r;
		unsigned short int g;
		unsigned short int b;
		unsigned short int undefined;

	} color;
	]]

	colour = ffi.typeof("color")

Oh here is a simple bin of a 2 colour aco for reference.

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0001 0002 0000 0202 0302 2222 0000 0000
3030 4746 3d3c 0000 0002 0002 0000 0202
0302 2222 0000 0000 0009 006d 0069 0064
006e 0069 0067 0068 0074 0000 0000 3030
4746 3d3c 0000 0000 000b 0067 0072 0065
0065 006e 0020 0066 0061 0064 0065 0000

The two colours are called "midnight" (2,3,34) and "green fade"(48,71,61)

That's not everything i need but it's a start. Now my issues are, i have no idea how to convert the ffi data types to their binary counterpart and save it out as a file. It's proving to be a very difficult thing to search for.

And also of course, i can't just save a txt file with the binary data in it, (tried that) it needs to be a proper binary file which i have no idea how to save.

Any help you can give would be greatly appreciated!

[airstruck]

Try converting the structs to strings and then writing the strings to the file (open the file in binary mode, see the manual).

The code to get a string from a struct should look something like this:

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local data = ffi.string(colour, ffi.sizeof(colour))

[Muzz]

Almost there!

http://hastebin.com/ulevukemij.lua

This is the code. You can see that im concatenating the strings, and data together and that works fine. Now the last bit of the puzzle is working out why the bits seem to be exporting numbers incorrectly. At first i thought it was an endian issue, but it seems like i was wrong there.

https://drive.google.com/file/d/0B-qJDC ... sp=sharing

Here is the aco file i'm trying to replicate, and there is my attempt so far.

So for some reason it is outputting a short with a value of 2 as 0200 instead of 0002, or a value of 3 as 0300 instead of 0302

[Nixola]

It's probably because the pc uses little endian internally.

[Muzz]

So i worked it out.

The colour format didn't care about endianess. The version and colour count did, but swapping bits with a short didn't work with bit.swap, but that was just a matter of i*256. The long ints however i could use bit.swap.

I'll post up my code when i clean it up in case it's handy for anyone else.