Map image data and file names

Minotorious · May 5th 2017

I did some experimenting and I wanted you to confirm a few things for me @red51 if you can.

1)
each gunzip decompressed mt_* file consists of 262144bytes.
Now each image pixel takes up 3 bytes of space (hex colour) and a 4th FF byte defining the end of the hex colour code correct?
If yes then that means that each image consists of 65536 pixels, which is nothing else that a 256x256 pixel image.

2)
how does the game know which square goes next to which? I assume it has to do with the way they are named, since looking inside the files there are no "excess" bytes to hold map position data, but could you provide some more information please?
My thought was something like the following (i.e. the first number means left/right position and the second number top/bottom with positive numbers towards top and right and negative towards bottom and left) but could you confirm it if I am correct or correct me if I am wrong?

mt_-2_2	mt_-1_2	mt_0_2	mt_1_2	mt_2_2
mt_-2_1	mt_-1_1	mt_0_1	mt_1_1	mt_2_1
mt_-2_0	mt_-1_0	mt_0_0	mt_1_0	mt_2_0
mt_-2_-1	mt_-1_-1	mt_0_-1	mt_1_-1	mt_2_-1
mt_-2_-2	mt_-1_-2	mt_0_-2	mt_1_-2	mt_2_-2

Miwarre · May 5th 2017

The fourth byte looks like an alpha value...

red51 · May 6th 2017

As @Miwarre suspected, the 4th byte is the alpha value. These are 256x256 8 bit RGBA images (i.e. 1 byte per color value [red, green, blue, alpha]). Maybe we will discard the alpha value in the future. Although this barely has an impact on the compressed image size, the uncompressed image will only have ~ 196.000 bytes then (so maybe it's a good idea to keep this in mind [e.g. before processing the image data, check the total amount of bytes after decompressing or something like that]).

About the coordinates, the first value is the X coordinate (horizontally), the second value the Z coordinate (vertically). Since the game uses a right-handed coordinate system (Z is forward, Y is up, X is left), you have to swap your X coordinates, so the map tiles would be arranged like that:

mt_1_1	mt_0_1	mt_-1_1
mt_1_0	mt_0_0	mt_-1_0
mt_1_-1	mt_0_-1	mt_-1_-1

Every map tile represents 3x3 chunks btw

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