Could the tool be used as a base for a diff viewer?

[Gildor]

Hi,
1) Only required assets are loaded. If uasset file holds only one asset inside, and you're clicking on it, only this asset will be loaded. Also referenced objects loaded - materials, textures. In my opinion, this happens quite fast.
2) You may open 2 umodels to see them side-by-side. There's no mode in umodel where you can see 2 models.
3) No thumbnails, sorry. I see it quite useless, because mesh is automatically positioned in viewport based on its bounds, and material rendering is very tricky (very far from exact representation in game).

[Gildor]

...
and here is the result:

Detected game root C:/UnrealTest/TheGame/Content
(...)
WARNING: Texture2D T_container_basic_wood1_N has no valid mipmaps

I think you've extracted everything from pak file, but there should be also .ubulk file which actually holds texture mipmaps (at least for PARAGON).

Apparently I can force the tool to display the file fast by providing a fake game root:

C:\UnrealTest\umodel_win32>umodel.exe -path=C:\UnrealTest\TheGame\Content\Items\Placeables\Meshes\SK_container_basic_wood1.uasset C:\UnrealTest\TheGame\Content\Items\Placeables\Meshes\SK_container_basic_wood1.uasset

"path" is not intended to accept package files, only directories. In your case this is a side effect of missing checks for parameter correctness, I think.

but would that not cause problems with eventual dependencies?

When you're loading just a single package with all referenced packages missing, you'll get warning messages in console, and dependencies (textures, materials etc) will be empty.

If I try to use "-obj" then all I get is the "Choose a package to open" UI.

-obj works nice for me. You should specify a package name in order to skip UI. However I see no point of specifying -obj for UE4 - every package has just a single object inside, so package name is enough.

What would be the actual command line parameters to use to correctly display one uasset

Example for "ARK: Survival Evolved"

Code:

umodel.exe -path=ARK\Content\PrimalEarth\Dinos\Raptor -game=ue4.5 raptor_Saddle_RIG.uasset -obj=raptor_Saddle_RIG

(-obj could be missing, as I said - it won't change anything for UE4)

[Gildor]

Understand. You're working with uncooked data. Textures are not working in this case - their data are in DDC (Derived Data Cache), and uasset files contains textures in png format which is not supported by UModel.