Add spline animation proposal. #1
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| # Spline Animation in USD | ||
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| This project aims to support spline animation on USD attributes. The project is | ||
| called **USD Anim** for short. |
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USD Anim seems to be a confusing name for the project? Why not USD Time Series if it lands in the ts implementation?
| scene description. Since many 3D applications represent varying values with | ||
| splines, it is a natural step to add splines to USD's vocabulary. | ||
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| **Gaming pipelines.** Game engines can work with spline data, and many are |
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nit: this might be a generalized assumption.
| | | Splines | Time Samples | | ||
| | ----------------- | --------------------------- | --------------------- | | ||
| | **Data format** | Curves defined by knots | Lookup tables | | ||
| | **Data density** | Sparse | Dense | |
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this might apply to complex animations but a liner 0->100 time sample animation can be sparse as well
| Hermite curves are non-parametric, and can be evaluated in constant time | ||
| via a simple cubic polynomial. | ||
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| - **General USD standards:** a contextually appropriate implementation. |
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| # Spline Animation in USD | ||
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| This project aims to support spline animation on USD attributes. The project is |
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Might be worth mentioning that Splines are also called Animation curves in the prelude. A lot of people coming from Maya might be more familiar with that term, whereas "spline" is often used to refer to a non-stepped curve in Maya parlance. I think a brief mention that they're the same thing might be beneficial for some folks.
| comes to mind, and they are not interpolated using spline math, but we still | ||
| call them splines. | ||
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| We refer to the points where curve segments join as _knots_. In a |
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It might be useful to have a labelled diagram here for clarities sake. I think your description is well written but may be a bit abstract to visualize.
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| - _Inner loops_ come from Presto. These specify a _prototype region_, which is | ||
| repeated a finite number of times before and/or after the prototype region. | ||
| The repeated portions are called the _echo region_. Inner loops use a mode |
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I don't think I fully understand the difference between a prototype region and an echo region, since both seem to get repeated? Or is the echo region the part of the time line that includes the animation repetition, while the prototype region is the area that is being repeated? so an echo region is fed by a prototype region?
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Also would source region perhaps be a more accessible term than prototype region?
| after the knots. Extrapolating loops support modes called _Repeat_, _Reset_, | ||
| and _Oscillate_, described below. | ||
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| It will be possible to use both systems in the same series. In that case, inner |
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Since the inner loop concept might be (to my knowledge) unique to Presto, it may be worth recommending/havng a baking system within USD to bake out either system into a non-looped series (ie the loops are still maintained, but loose their reference to the specific source region)
Thanks to Doug Epps at Apple for the suggestions.
Description of Proposal
Add spline animation to USD.
Contributing