Backlog/lib/ozz/ozz-animation/samples/playback/README.md

Ozz-animation sample: Animation playback

Description

Loads a skeleton and an animation from ozz binary archives. Then playbacks animation and renders the corresponding animated skeleton.

Concept

This sample loads ozz binary archive file (to read an animation and a skeleton). Ozz binary files can be produced with ozz command line tool fbx2ozz, or with ozz serializer (ozz::io::OArchive) from your own application/converter. At every frame the animation is sampled with ozz::animation::SamplingJob. Sampled local-space output is then converted to model-space matrices for rendering using ozz::animation::LocalToModelJob.

Sample usage

Some parameters can be tuned from sample UI:

• Play/pause animation.
• Fix animation time.
• Set playback speed, which can be negative to go backward.

Implementation

1. Load animation and skeleton.
   1. Open a ozz::io::OArchive object with a valid ozz::io::Stream as argument. The stream can be a ozz::io::File, or your custom io read capable object that inherits from ozz::io::Stream.
   2. Check that the stream stores the expected object using ozz::io::OArchive::TestTag() function. Object type is specified as a template argument.
   3. De-serialize the object with >> operator.
2. Allocates runtime buffers (local-space transforms of type ozz::math::SoaTransform, model-space matrices of type ozz::math::Float4x4) with the number of elements required for the skeleton. Note that local-space transform are Soa objects, meaning that 1 ozz::math::SoaTransform can store multiple (4) joints.
3. Allocates sampling context (ozz::animation::SamplingJob::Context) with the number of joints required for the animation. This context is used to store sampling local data as well as optimizing key-frame lookup while reading animation forward.
4. Sample animation to get local-space transformations using ozz::animation::SamplingJob. This job takes as input the animation, the context and a time at which the animation should be sampled. Output is the local-space transformation array.
5. Convert local-space transformations to model-space matrices using ozz::animation::LocalToModelJob. It takes as input the skeleton (to know about joint's hierarchy) and local-space transforms. Output is model-space matrices array.
6. Model-space matrices array can then be used for rendering (to skin a mesh) or updating the scene graph.