Mipzip file format specification

The Mipzip file format is a simple format for storing all mipmap levels of a texture on a hard drive compressed, in a single Zip file, but able to be loaded efficiently.

In Libvob, reading mipzip files is implemented by the class org.nongnu.libvob.gl.MipzipFile, around which more sophisticated classes (such as org.nongnu.libvob.gl.MipzipLoader are built.

The current format, V1.0, is defined as follows.

The Zip file shall contain two constant entries and a variable number of mipmap level entries. The constant entries are

texformat: The texture format used in the file. The comment of this entry (not the entry contents!) stores the OpenGL token string, without the GL_ prefix, for example COMPRESSED_RGB_S3TC_DXT1_EXT or RGB.
internaltexformat: (optional - not used for compressed textures) The recommended internalformat token to give OpenGL for this texture. E.g. RGB4
datatype: (optional - not used for compressed textures) Specifies the data type to give to the OpenGL texImage2D command. E.g. UNSIGNED_SHORT_5_6_5
origsize: The size of the original image inside this mipzip, as (texcoord1)x(texcoord2), e.g., 0.99609375x0.9990234375

It is possible that later versions shall add more constant fields, and a version number identifier.

The variable fields have as their name the integer level index (zero-based), and as their content the direct binary data. As their comment they have a string (width)x(height),

Altogether, this gives the mipzip file reader enough information to call glTexImage2D or glCompressedTexImage2D.

Example: the output of unzip -l on an archive:

Archive:  /hdd/6/tmpimg/urn_-_x-storm_-_1.0_-_application__pdf,abslyr6tzv4z4fxbfcdpxcvavyc7cioa.43ffr2a4w44d3yew3fabmxj3srcu2ehdclgye5q-240x186-1
  Length     Date   Time    Name
 --------    ----   ----    ----
        0  08-26-03 16:03   texformat
COMPRESSED_RGB_S3TC_DXT1_EXT
        0  08-26-03 16:03   origsize
0.99609375x0.9990234375
  2097152  08-26-03 16:03   0
2048x2048
   524288  08-26-03 16:03   1
1024x1024
   131072  08-26-03 16:03   2
512x512
    32768  08-26-03 16:03   3
256x256
     8192  08-26-03 16:03   4
128x128
     2048  08-26-03 16:03   5
64x64
      512  08-26-03 16:03   6
32x32
      128  08-26-03 16:03   7
16x16
       32  08-26-03 16:03   8
8x8
        8  08-26-03 16:03   9
4x4
        8  08-26-03 16:03   10
2x2
        8  08-26-03 16:03   11
1x1
 --------                   -------
  2796216                   14 files