Add support of deformation motion blur

[hshakula]

PURPOSE

Adds support of deformation motion blur

EFFECT OF CHANGE

• Added support of deformation motion blur in the Full quality.
• New geometry render setting introduced - "Geometry Time Samples". The number of sub-frame samples to compute when rendering deformation motion blur over the shutter open time. The default is 1 (sample only at the start of the shutter time), giving no deformation blur by default. If you want rapidly deforming geometry to blur properly, you must increase this value to 2 or more. Note that this value is limited by the number of sub-samples available in the USD stage being rendered. Set to 0 to get all sub-samples available in the USD stage.

TECHNICAL STEPS

• Use HdSceneDelegate::SamplePrimvar instead of HdSceneDelegate::Get to query the required amount of time samples from the scene delegate.
• Add new geometry setting - rpr:geomSamples.

NOTES FOR REVIEWERS

Support for UsdSkel deformation blur can be quite easily added for USD 21.05+ only. Because there was no appropriate API to get few samples for a HdComputation before. It was only recently implemented and merged - PixarAnimationStudios/OpenUSD#1455.

So I plan to open this pull request and move on to adding support of USD 21.05 in our plugin (there are many changes actually). After that, I will implement the UsdSkel deformation motion blur support.

[bsavery]

Still in progress?

[hshakula]

I don't plan to add anything to this PR. UsdSkel deformation blur will be in a separate PR.

[bsavery]

My only concern is the motion samples setting. People may intuitively set to 0 to get no motion blur. However I don't see a better option here other than noting in the UI

[hshakula]

Well, we can change samples range from [0; inf] to [1; inf] and remove this automatic behavior for 0 (when we get all available samples). At least because this does not make sense in the case of UsdSkel where we can generate an infinite amount of samples.

[bsavery]

Ok I think that makes more sense.

[bsavery]

Hey @hshakula can you fix the merge conflicts

[hshakula]

@bsavery, done