This topic was archived here:

https://web.archive.org/web/20230000000000fw_/https://www.zenhax.com/viewtopic.php?t=3059

Karlovsky120, posted Mon Sep 05, 2016 7:09 pm (17247)

---

I'm writing a small program that requires images of inventory items. Now, I don't want to bundle that data with the program (firstly, it's not mine, secondly, the project will be more future-proof if I do as explained below).

What I want to do is open the resource.assets where those images reside (in a single 2DTexture object), extract the object, transform it into a more standard image format (for example a png) and use that in my program.

The problem I have encountered is that I don't understand the 2DTexture object structure. I think that first 8 bytes are the height and the width of the texture (I converted it to PNG with a tool to which source I have no access and the image size was 4096*4096). Since the size of the file is 67.108.936 bytes and 4096*4096 = 16.777.216 and 16.777.216 * 4 = 67.108.864 I can assume that each pixel is represented with 4 bytes (RGBA maybe?). There are also 67.108.936 - 67.108.864 = 72 bytes of metadata. First eight seem to be the size, but I'm not sure what the rest 64 represent. Here are the first 72 bytes:

Code:

00 10 00 00   00 10 00 00   00 00 00 04   05 00 00 00
01 00 00 00   01 01 00 00   01 00 00 00   02 00 00 00
01 00 00 00   01 00 00 00   00 00 00 00   00 00 00 00
00 00 00 00   00 00 00 00   00 00 00 04   00 00 00 00
00 00 00 00   00 00 00 00

I'm aware that some of the 72 bytes might be in the end of the file, but the texture I'm looking at has at least a few rows of pixels on the top and the bottom completely white. Given that there are only zeros for several thousand bytes after the part I copied and file ends with several thousand bytes of zeroes as well, I can assume that the part above is all of the metadata. I can also assume that four zeros mean white, and since it holds images that go into inventory slots, I can also assume that it's completely translucent.

Here is an example of the rest of the file:

Code:

ff cf 6b 41   ff e6 87 5b   ff f6 9a 6b   ff f1 93 66
ff f8 9f 70   ff fc b1 80   ff ff b8 87   ff fb a7 77
ff eb 8f 61   ff de 83 58   ff e0 89 5c   ff e3 8d 60
ff d9 86 59   ff ca 7f 54   ff e3 99 69   f2 cf 88 5e
9d 6e 3d 28   79 76 48 30   00 ae 65 40   00 99 63 43
00 9a 6d 4c   00 cd 8c 60   00 6e 48 30   00 6f 52 38
00 a6 60 3d   00 8c 59 3b   00 8a 5c 3e   00 56 3e 2a
00 b7 76 4f   00 54 2c 1b   00 a0 56 35   00 95 5d 3b
00 82 4d 2f   00 4d 30 1f   00 bf 7e 54   00 71 50 37
00 88 60 42   00 cd 8c 5f   00 84 59 3c   00 37 17 09
00 bc 73 4f   00 82 54 3c   00 7e 4f 39   00 b5 69 47
00 4d 21 0f   00 6b 44 2d   00 b5 6a 44   00 97 60 41
00 8c 5d 41   00 b8 6b 49   00 fe fe fe   00 fb fb fb
02 fc fc fc   07 f6 f7 f6   0f eb ec ec   1b db dc dd
6f c6 c9 c8   b6 a4 a7 a8   f0 95 98 9a   ff a6 a7 a9
ff b5 b4 af   ff 99 97 8e   ff 75 71 6b   ff 69 67 65
ff 75 77 78   ff 8e 8f 90   ff b2 b6 ba   ff d5 da db
ff cb d4 d7   ff aa b2 b6   ff 59 5c 61   ff 2b 2c 2e
ff 2e 2e 2e   ff 2d 2d 2d   ff 32 32 33   ff 40 43 46
ff 63 69 6c   ff 9e a4 a6   ff d6 dd de   ff e4 e5 e6
ff e8 e9 ea   ff d0 d2 d2   ff c5 ca cc   f1 c1 c6 cc
c3 c4 cb cf   8e cd d1 d3   56 df e2 e3   21 ec ed ef
13 ef f1 f2   0c f5 f6 f7   07 f9 f9 fa   04 fb fc fc
02 fd fe fe   01 fe fe fe   00 fd fd fd   00 fd fd fd
01 fe fd fd   06 f9 f8 f5   12 ee ea e3   4b e7 e0 d6
d2 b7 a5 88   ff 9d 84 5d   ff a5 8d 67   ff a9 92 6d
ff ac 97 72   ff bd a8 84

I'm not really that well versed in structures of different image formats so I don't know what type of metadata they tend to carry. Do any of you know what could this 72-bytes of data mean, as well as how might a single pixel be structured with it's 4 bytes?

Karlovsky120, posted Tue Sep 06, 2016 2:05 am (17251)

---

Well, I managed to figure it our, sort of. I still have no idea what those 64 bytes mean.

I pulled all the pixel data into my program and constructed a ARGB image from it. It had weird colors and was flipped upside down. Then I swapped each 1st and 4th pixel byte. Picture looked a lot better. I tried swapping 2nd and 3rd pixel bytes and viola, picture had normal colors. It seems it was a BGRA image. I then flipped it and it looked exactly as it should. I could then extract specific items from fixed-up image.

Only problem I have left is that when I'm accessing data from the asset bundle, I specify exact byte where the image starts. Which will work great until the next game update when everything might get shifted due to new asset additions. This isn't really a matter for this subforum, but is there some kind of an index in the bundle file header that would point me to the right location?

Anyway, as far as this thread goes, I have resolved my problem.