HowTo
To open a usd file with usdtweak, you can use usdtweak's file browser under File / Open :
It will let you open the file either as a layer or as a stage, with the option of loading the payload when you open the stage. Opening as a layer can be helpful in situation where the renderer or hydra crashes with the stage, it lets you open the usd file without composing the stage, and let you fix the problem. Using 'Open as stage' will load only scene layer properties and metadata, no geometry will be loaded, this is also useful for opening inspecting a large scene without the overhead of loading all geometry.
To load the stage after opening right click the file in the content browser and select 'Load as stage'
Alternatively you can drag and drop a usd file from the system file browser to usdtweak, it will be opened as a layer.
Unchecking 'Load payload' defers the loading of any payload in the scene, this is useful for inspecting large scenes when loading all geometry isn't required.
The easiest way to assign a material to a prim is to use the Stage property editor. On selected prim which allow material assigned, you should see a Material binding section with the different bindings per purpose.
Clicking on the cog will show the list of all materials available in the stage and clicking on one of them will assign it to the selected prim for the particular purpose.
