# Overview of Release 3.6

- New Features
  - Modern Graphics APIs and Parallel Computation
  - Updated Third-party APIs and Tools
- API Additions
  - Additions to Osd::PatchShaderSource
  - Osd extensions for patch evaluation from client shaders and compute kernels
- Other Changes
  - Deprecation Announcements
  - Improvements
  - Bug Fixes

### New Features

The purpose of this release is to address concerns which improve support for current typical use cases and provide support for significant new use cases.

#### Modern Graphics APIs and Parallel Computation

OpenSubdiv is organized as a set of components for working with subdivision surface representations, i.e. Bfr, Far, Vtr, Sdc along with a collection of back-end components in Osd supporting the use of specific low-level subsystems to work with subdivision surface data.

These back-end components in Osd have taken many forms including in some cases specific complete GPU shaders along with controller classes to manage compilation and execution of these shaders.

In practice it has been more effective for Osd to simply supply the functions needed to operate on subdivision surface data, allowing the client application or client library to take care of using these functions from client provided shaders and computation kernels using client provided execution controllers.

This has been the direction for the Osd library for some time and the changes implemented in this release make this even more straightforward.

The existing methods:

> - Osd::GLSLPatchShaderSource::GetPatchBasisShaderSource()
> - Osd::HLSLPatchShaderSource::GetPatchBasisShaderSource()
> - Osd::MTLPatchShaderSource::GetPatchBasisShaderSource()

continue to return shader source strings at runtime which contain definitions and functions allowing client shader code to evaluate values and first and second derivatives on the piecewise parametric patches resulting from subdivison refinement.

The identical code is now available at compile time as:

> - opensubdiv/osd/patchBasis.h

and is essentially a "shader" interface that can be used from client kernels including those implemented using TBB, CUDA, C++, etc.

Similarly, the new methods:

> - Osd::GLSLPatchShaderSource::GetPatchDrawingShaderSource()
> - Osd::HLSLPatchShaderSource::GetPatchDrawingShaderSource()
> - Osd::MTLPatchShaderSource::GetPatchDrawingShaderSource()

return shader source strings at runtime which contain definitions and functions allowing clients to draw the piecewise parametric patches resulting from subdivision, e.g. using GPU tessellation shaders or GPU mesh shaders.

The returned shader source has been stripped of resource binding and other potentially problematic defintions since these are usually best handled by client shader code.

These methods have been tested successfully with new client code using Vulkan and DirectX 12 in addition to existing client code using OpenGL, Metal, DirectX 11, etc.

#### Updated Third-party APIs and Tools

While the methods described above will be the most effective way to use OpenSubdiv, some of the existing back-end components have been updated to accommodate evolving third-party APIs and tools.

Specifically, the TBB implementation has been updated to allow use with the oneTBB API while continuing to maintain compatibility with earlier releases of TBB.

Also, there have been minor fixes to the CMake build to accommodate using the Ninja build system and also systems with OpenCL 3.0.

### API Additions

See associated Doxygen for full details.

#### Additions to Osd::PatchShaderSource

> - GLSLPatchShaderSource::GetPatchDrawingShaderSource()
> - HLSLPatchShaderSource::GetPatchDrawingShaderSource()
> - MTLPatchShaderSource::GetPatchDrawingShaderSource()

#### Osd extensions for patch evaluation from client shaders and compute kernels

> - struct OsdPatchArray and OsdPatchArrayInit()
> - struct OsdPatchCoord and OsdPatchCoordInit()
> - struct OsdPatchParam and OsdPatchParamInit()
> - OsdPatchParamGetFaceId()
> - OsdPatchParamGetU()
> - OsdPatchParamGetV()
> - OsdPatchParamGetTransition()
> - OsdPatchParamGetBoundary()
> - OsdPatchParamGetNonQuadRoot()
> - OsdPatchParamGetDepth()
> - OsdPatchParamGetParamFraction()
> - OsdPatchParamIsRegular()
> - OsdPatchParamIsTriangleRotated()
> - OsdPatchParamNormalize()
> - OsdPatchParamUnnormalize()
> - OsdPatchParamNormalize(Triangle)
> - OsdPatchParamUnnormalizeTriangle()
> - OsdEvaluatePatchBasisNormalized()
> - OsdEvaluatePatchBasis()

### Other Changes

#### Deprecation Announcements

> - The methods Osd::TbbEvaluator::SetNumThreads() and Osd::OmpEvaluator::SetNumThreads() have been marked deprecated.

#### Improvements

> - Updated Osd patch drawing shader source to exclude legacy shader constructs to improve compatibility with Vulkan, DX12, etc. (GitHub #1320)
> - Installed Osd patch evaluation headers to allow use from client shaders and compute kernels (GitHub #1321)
> - Updated CMake build to locate TBB using TBB's CMake config in order to support oneTBB (GitHub #1319)
> - Updated CMake FindOpenCL module to support parsing version information from recent OpenCL headers (GitHub #1322)
> - Removed obsolete .travis.yml (GitHub #1324)

#### Bug Fixes

> - Fixed inconsistent warning levels for MSVC builds when using Ninja (GitHub #1318)
> - Fixed documentation build errors when using Ninja (GitHub #1323)
> - Fixed build errors resulting from oneTBB API changes (GitHub #1317)

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