The mod contains the following folders that are hopefully self explanatory:
Step 1 - Find the Bundle
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Find your portrait bundle. This will be located in "YourDriveHere\SteamLibrary\steamapps\common\Warhammer 40,000 Rogue Trader\Bundles\portraits". Yes it has no extension.
Copy it.
Paste it into the Updated Bundle Folder.
Step 2 - Load the Bundle
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Open UABEA. Load the portrait file in your Updated Bundle Folder.
Note: You need to use Open rather than Load Package File.
A message will appear:
Click Memory.
This uncompresses the bundle. You will now have this:
Click Info.
Step 3 - Filter
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You are now confronted with the Asset window. We are only interested in Texture2D in this case. So let's filter for that:
Uncheck AssetBundle and Sprite, and close the Type Filter window. We will now only see portrait textures in the Asset window.
Step 4 - Importing
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Finally we get to the import part and this is made simple because of the wacky names of the portraits I've included.
Select All Portraits in the Asset Info window.
Click Plugins.
Now you will get the Plugins window. Select Batch import textures and click OK.
From here you get a file selection window. Navigate yourself to 1 - Edited Portraits/Texture2D and hit Select Folder. You will not see any items!
Here is the beauty of the setup, all you have to do is: select all and hit OK.
Step 5 - Saving
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You have now imported everything you need and just need to save. Select Save from the Assets Info window.
You will get a popup informing you you're not done. Hit OK.
Close the Asset Info window.
Select Save at the main UABEA window:
Important: close the bundle via File: Close. You need to do this for the next phase to work properly!
Step 6 - Compression
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First open the bundle you just saved.
Select File:Compress:
You will get a folder selection window here.
Name the file portraits.
Navigate yourself to the 3 - Compressed Bundle folder.
Hit Save.
You will now get to choose compression. In my tests LZ4 is probably what OwlCat uses. LZMA causes a noticeable increase in load times. (Only at game start.)
Pick LZ4 and wait for it to finish.
Step 7 - Replace Game Bundle
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Copy your compressed portraits bundle from "3 - Compressed Bundle" to "YourDriveHere\SteamLibrary\steamapps\common\Warhammer 40,000 Rogue Trader\Bundles\".
Optionally: rename the original to portraits_old or something.
PLAY GAME without trash portraits.