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radv: Configure implicit VS primitive ID to be a per-primitive output.

Timur Kristóf requested to merge Venemo/mesa:radv_ngg_primitive_id_per_prim into main

Based on !32220 (merged)

GFX10.3 and newer GPUs support per-primitive outputs, which thus far we've only used for implementing per-primitive mesh shader outputs. However, these can be also very useful to implement the implicit VS primitive ID.

Benefits of this approach:

  • We don't have to disable provoking vertex reuse, which results in more efficient vertex processing.
  • There is no LDS access needed to export the primitive ID, because it is already available to GS threads.
  • As a consequence of not needing LDS, we can use this together with NGG passthrough mode.
Edited by Timur Kristóf

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