To establish the time range over which values are animated, the root layer can specify a start and end time in its layer metadata. USD represents animation as time-sampled attribute values. Here, we will create the USD files by hand to illustrate the underlying concepts.
In a typical production pipeline, rigging & animation would be set up in a dedicated package and the results exported to USD. Moving Objects with Animated Transformations: Spinning the Top In the examples here, we use +Z as the up axis, and write this choice out in every file so that they will work regardless of your site configuration. Common choices are +Y and +Z.Īs a pipeline interchange format, USD provides ways to configure a site default, as well as to store an explicit choice per-file. Running usdview on the file, we can see that the geometry looks like this:Ĭomputer graphics pipelines almost always pick an axis to represent the "up" direction. The USD distribution ships with usdview, a lightweight tool for inspecting USD files. (See the Houdini USD Plugins for details.) The model was exported to the file USD/extras/usd/tutorials/animatedTop/ using the Usd Export ROP. The toy geometry was modeled in Houdini as a revolved curve, followed by per-face color assignments as Houindi vertex attributes. Run generate_examples.py in that directory to generate all of the snippets for each step shown below. The scripts and data files exist in the USD distribution under USD/extras/usd/tutorials/animatedTop. To fully illustrate these concepts, we walk through a Python script that performs these steps using the Python USD API, as well as showing the resulting text USDA outputs. We create the scene by starting with a USD file with static geometry, referencing it into another USD file, overlaying animation, and then using a third USD file to reference and re-time that animation. Chaining Multiple Transformations with xformOpOrder.Moving Objects with Animated Transformations: Spinning the Top.
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