
The Gallium3D feature levels pair closely to DirectX version numbers and their capabilities, such as with regard to the availability of fragment shaders, vertex shaders, maximum texture dimensions, two-sided stencil, and other technical features. These seven Gallium3D feature levels also state which support OpenCL 1.0, OpenGL 4.0/3.2/3.0, etc. Beyond just defining these levels, Zack has also added a parameter to the Gallium3D infrastructure so that drivers can expose which feature level they support.
This work and the resulting discussion can be found in this Mesa mailing list thread.
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