PocketBook Themes
PocketBook devices support "theming", in the sense that you can change the way the UI looks and is arranged to a great degree.
However themes aren't documented. Although PocketBook have provided a command-line tool called "pbres" to read and write theme files, it was only ever provided for Windows. Several other open source clones of this tool have since appeared which can build and run on Macs and Linux, and even Windows. Here are some that I've found:
- https://github.com/Enyby/pbres
- https://github.com/yuryfdr/xpbres
- https://github.com/Lighting/pbtheme (only extracts the uncompressed text)
- https://github.com/chrisridd/pbtools (I wrote my own cross platform version in rust)
They all work mostly the same way.
The official PocketBook SDK includes a native ARM binary of "pbres" but it is unclear what that supports. The internal strings suggest it was built in 2020, and the arguments are different to the Windows "pbres.exe".
[edit] Theme files
Theme files have a ".pbt" extension, and have a proprietary binary format. I will use the Line.pbt resource that ships with the Inkpad Color 3 (6.8 firmware) in the following examples. (It is in the /ebrmain/themes directory.) I will also use Enyby's pbres, because it is very easy to build.
The compiled "*.pbt" theme files start with a magic identifying string, a version field, a little-endian header length, and a list of headers for each resource. Then there's a compressed section for each resource.
| offset | bytes | value |
|---|---|---|
| 0 | 15 | magic identifier "PocketBookTheme" |
| 15 | 1 | file version - always 0x01 |
| 16 | 4 | total size of all resource headers |
Each resource header has 3 32-bit unsigned little-endian integers. The first resource (the theme configuration) has no name, but all others have NUL-terminated names. Each header is a multiple of 4 bytes in size.
| offset | bytes | value |
|---|---|---|
| 0 | 4 | uncompressed size |
| 4 | 4 | file offset to compressed resource |
| 8 | 4 | compressed size |
| 12 | variable | name of resource |
Each resource is then separately compressed with zlib (RFC 1950)
$ pbres -l Line.pbt resource size compressed -------------------------------------------- <theme.cfg> 193900 31671 AppStore:4 23416 2898 CardLogo:4 248460 75326 GooglePlay:4 25288 3020 about:4 15136 669 activate_account_on_eink:4 61264 705 activate_account_on_smartphone:4 61264 1301 add_to_cloud:4 15136 1158 adjustments:4 15136 168 adjustments_inv:4 15136 801 adobe_activation_layout:4 11342 1170 [... lots more resources omitted ...] wwbishop:4 18368 2198 wwking:4 18368 2638 wwknight:4 18368 2396 wwpawn:4 18368 1885 wwqueen:4 18368 3219 wwrook:4 18368 2009 zoom_in:4 15136 1051 zoom_out:4 15136 1034
In this version of Line.pbt there are over 1400 resources.
Many of the resources are images, and the appended ":4" seems to indicate their bit depth. The internal format for an image is described in the PocketBook SDK and is proprietary, however the pbres tools try to convert them to and from Windows BMP files. However they all get the resource format wrong and write garbage. The xpbres tool can write xpm files instead. Correct image format converters are found in pbtools.
You can extract a raw resource by name, eg "pbres -u Line.pbt wwrook:4"
You can also dump an entire theme file, eg "pbres -d Line.pbt" which will create subdirectories containing all the images converted to BMP. However! Not all resources are images, and most tools just crash if they try to convert one of these resources to BMP. An example above is "adobe_activation_layout:4". Let's unpack it and see:
$ ../pbres/pbres -u Line.pbt adobe_activation_layout:4 $ file adobe_activation_layout:4 adobe_activation_layout:4: JSON data
So not an image after all, and indeed it does look like JSON...
{"AppLoginView" : {"class" : "PBDialog","background_color" : 16777215,"info_label" : {"class" : "PBLabel","window_pos" :
[...]
I have also seen TrueType fonts being embedded as resources.
[edit] Config file
The "<theme.cfg>" file that's extracted has an INI file-style syntax. The one in Line.pbt is just over 5000 lines long. Nothing seems to refer to the other resources by name.
There is some translated documentation of the text configuration format in another MobileRead forum thread.
What happens if you install an old theme on a new device? Are the themes hard coded to screen sizes?
