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In 2017, to accommodate developers’ increasing appetite for migrating geometry work to compute shaders, AMD introduced a more programmable geometry pipeline stage in their Vega GPU that ran a new type of shader called a primitive shader. According to AMD corporate fellow Mike Mantor, primitive shaders have “the same access that a compute shader has to coordinate how you bring work into the shader.” Mantor said that primitive shaders would give developers access to all the data they need to effectively process geometry, as well.
Primitive shaders led to task shaders, and that led to mesh shaders."
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Mesh shaders will expand the capabilities and performance of the geometry pipeline. Mesh shaders incorporate the features of Vertex and Geometry shaders into a single shader stage through batch processing of primitives and vertices data before the rasterizer. The shaders are also capable of amplifying and culling geometry."
"The mesh shader outputs triangles that go to the rasterizer. It’s just a set of threads and it’s up to the developer how they work. With a mesh shader, you program in a group with many threads working together in cooperation rather than locally. When finished, it outputs a small index triangle list. All threads do individual things and vertex data remains unchanged."
Not just Alex, how much difference it will make is unclear though, maybe not much. I think SFS is a far bigger deal.