31 lines
2.2 KiB
Markdown
31 lines
2.2 KiB
Markdown
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# Ozz-animation sample: Skinning
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## Description
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This sample adds skinning to the playback sample. It loads a skeleton, an animation and skinned meshes from ozz binary archives. It playbacks animation every frame and uses model-space matrices to build skinning matrices and render a skinned mesh.
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## Concept
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This sample is based on playback sample for the most part, reading and sampling an animation. In addition it loads an ozz binary mesh file which was generated with sample_fbx2mesh tool.
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At every frame, once the animation is sampled and model-space matrices computed, skinning matrices are built. Skinning matrices are the composition (multiplication) of model-space and mesh inverse bind pose matrices. This step can be seen as allowing to transform vertices into joint's local-space, so they can be transformed by this joint.
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## Sample usage
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Animation playback parameters can be tuned from sample UI:
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- Play/pause animation.
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- Fix animation time.
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- Set playback speed, which can be negative to go backward.
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Rendering options are also exposed:
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- Enabling skeleton display.
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- Enabling mesh display.
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- Enabling skinning stage.
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- Display normals, tangent and binormals.
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## Implementation
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1. Load animation and skeleton, sample animation to get local-space transformations, and finally convert local-space transformations to model-space matrices. See Playback sample for more details about these steps.
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2. Load meshes from ozz archive. There can be multiple meshes as import utility (aka fbx2mesh) maintains dcc file meshes split.
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3. Computes and allocates skinning matrices. Number of skinning matrices might be less from the number of joints, as a mesh might be skinned by a subset of all skeleton joints only. Mesh::joint_remaps is used to know how to order skinning matrices, hence is size defines their number.
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4. Skinning matrices array is updated before rendering each mesh. A skinning matrix is the multiplication of the model-space and the mesh inverse bind pose matrix for a joint. Mesh::joint_remaps is used to index skeleton joints, so they match with the mesh.
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5. Skinning is performed by ozz::geometry::SkinningJob. Please check sample framework DrawSkinnedMesh function for more details about how to setup that job.
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