nv2a: Rewrite primitives on client

[mborgerson]

Not all Vulkan implementations support geometry shaders (e.g. MoltenVK, KosmicKrisp). As a step towards enabling xemu on such implementations, move primitive rewriting out of geometry shaders and just do it client side when necessary.

Work in progress.

[gemini-code-assist]

Summary of Changes

Hello @mborgerson, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the NV2A graphics pipeline by shifting primitive rewriting from geometry shaders to the CPU. This change enhances compatibility with various Vulkan implementations, particularly those lacking geometry shader support, and streamlines the graphics rendering process by centralizing primitive decomposition. The previous GPU property detection mechanism has been removed as it is no longer relevant to the new client-side approach.

Highlights

• Client-Side Primitive Rewriting: Moved the logic for rewriting graphics primitives (like triangle strips, fans, quads, and polygons) from GPU geometry shaders to the CPU client-side. This change allows for broader compatibility with Vulkan implementations that may not support geometry shaders, such as MoltenVK.
• Removal of GPU Property Detection: Eliminated the gpuprops.c files and associated code responsible for dynamically determining GPU geometry shader winding properties. This information is no longer needed as primitive rewriting is now handled on the CPU.
• Simplified Shader Generation: The GLSL geometry shader generation logic has been significantly simplified, as it no longer needs to handle complex primitive types or their specific provoking vertex rules. The shaders now primarily deal with basic points, lines, and triangles.
• Integration into Rendering Paths: The new client-side primitive rewriting functions (pgraph_prim_rewrite_ranges, pgraph_prim_rewrite_indexed, pgraph_prim_rewrite_sequential) have been integrated into both the OpenGL and Vulkan rendering paths to process drawing commands before they are sent to the GPU.

Changelog

• hw/xbox/nv2a/pgraph/gl/draw.c
  • Included 'prim_rewrite.h' for new primitive rewriting functions.
  • Added logic to retrieve ShaderPolygonMode and PROVOKING_VERTEX settings.
  • Integrated pgraph_prim_rewrite_ranges and pgraph_prim_rewrite_indexed to rewrite draw arrays and inline elements into basic triangles/lines when necessary, using glDrawElements instead of glMultiDrawArrays.
• hw/xbox/nv2a/pgraph/gl/gpuprops.c
  • Removed file, eliminating GPU property detection logic.
• hw/xbox/nv2a/pgraph/gl/meson.build
  • Removed 'gpuprops.c' from the build configuration.
• hw/xbox/nv2a/pgraph/gl/renderer.c
  • Removed calls to pgraph_gl_determine_gpu_properties during context initialization.
  • Removed the get_gpu_properties function pointer from the GL renderer operations.
• hw/xbox/nv2a/pgraph/gl/renderer.h
  • Included 'prim_rewrite.h'.
  • Added gl_prim_rewrite_buffer and prim_rewrite_buf members to PGRAPHGLState.
  • Removed declarations for pgraph_gl_determine_gpu_properties and pgraph_gl_get_gpu_properties.
• hw/xbox/nv2a/pgraph/gl/shaders.c
  • Simplified get_gl_primitive_mode to only return GL_POINTS, GL_LINES, and GL_TRIANGLES, as complex primitive types are now rewritten client-side.
• hw/xbox/nv2a/pgraph/gl/vertex.c
  • Generated and initialized gl_prim_rewrite_buffer and prim_rewrite_buf.
  • Finalized gl_prim_rewrite_buffer and prim_rewrite_buf during buffer cleanup.
• hw/xbox/nv2a/pgraph/glsl/geom.c
  • Included 'prim_rewrite.h'.
  • Updated state->primitive_mode using pgraph_prim_rewrite_get_output_mode.
  • Removed first_vertex_is_provoking from GeomState.
  • Simplified geometry shader generation logic, removing specific handling for TRIANGLE_STRIP, TRIANGLE_FAN, QUADS, QUAD_STRIP, and POLYGON primitive types.
  • Removed get_vertex_order helper function and related vertex reordering logic.
• hw/xbox/nv2a/pgraph/glsl/geom.h
  • Removed first_vertex_is_provoking, tri_rot0, and tri_rot1 fields from the GeomState struct.
• hw/xbox/nv2a/pgraph/meson.build
  • Added 'prim_rewrite.c' to the build configuration.
• hw/xbox/nv2a/pgraph/pgraph.h
  • Removed the GPUProperties struct definition.
  • Removed the get_gpu_properties function pointer from PGRAPHRendererOps.
• hw/xbox/nv2a/pgraph/prim_rewrite.c
  • Added new file implementing pgraph_prim_rewrite_init, pgraph_prim_rewrite_finalize, pgraph_prim_needs_rewrite, pgraph_prim_rewrite_get_output_mode, and various rewrite_* functions for different primitive types (lines, strips, fans, quads, polygons).
  • Implemented pgraph_prim_rewrite_ranges and pgraph_prim_rewrite_indexed to handle primitive rewriting and provoking vertex placement.
• hw/xbox/nv2a/pgraph/prim_rewrite.h
  • Added new header file defining PrimRewriteBuf and PrimRewrite structs.
  • Declared functions for primitive rewriting: pgraph_prim_rewrite_init, pgraph_prim_rewrite_finalize, pgraph_prim_needs_rewrite, pgraph_prim_rewrite_get_output_mode, pgraph_prim_rewrite_ranges, pgraph_prim_rewrite_indexed, and pgraph_prim_rewrite_sequential.
• hw/xbox/nv2a/pgraph/vk/buffer.c
  • Initialized prim_rewrite_buf during Vulkan buffer initialization.
  • Finalized prim_rewrite_buf during Vulkan buffer finalization.
• hw/xbox/nv2a/pgraph/vk/draw.c
  • Included 'prim_rewrite.h'.
  • Simplified get_primitive_topology to return only VK_PRIMITIVE_TOPOLOGY_POINT_LIST, VK_PRIMITIVE_TOPOLOGY_LINE_LIST, and VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST.
  • Added logic to retrieve ShaderPolygonMode and PROVOKING_VERTEX settings.
  • Integrated pgraph_prim_rewrite_ranges, pgraph_prim_rewrite_indexed, and pgraph_prim_rewrite_sequential to rewrite draw arrays, inline elements, and inline buffers into basic primitives, using vkCmdDrawIndexed when rewriting is applied.
• hw/xbox/nv2a/pgraph/vk/gpuprops.c
  • Removed file, eliminating GPU property detection logic.
• hw/xbox/nv2a/pgraph/vk/meson.build
  • Removed 'gpuprops.c' from the build configuration.
• hw/xbox/nv2a/pgraph/vk/renderer.c
  • Removed calls to pgraph_vk_determine_gpu_properties during renderer initialization.
  • Removed the get_gpu_properties function pointer from the Vulkan renderer operations.
• hw/xbox/nv2a/pgraph/vk/renderer.h
  • Included 'prim_rewrite.h'.
  • Added prim_rewrite_buf member to PGRAPHVkState.
  • Removed declarations for pgraph_vk_determine_gpu_properties and pgraph_vk_get_gpu_properties.

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[gemini-code-assist]

Code Review

This pull request is a significant and valuable change that refactors primitive rewriting from geometry shaders to the CPU. This improves compatibility with Vulkan implementations that do not support geometry shaders, such as MoltenVK. The implementation is well-structured, with the new logic encapsulated in prim_rewrite.c.

I've found a few issues related to provoking vertex handling for complex primitives like quads and polygons, which could lead to incorrect flat shading. I've added specific comments with suggestions to address these.

Overall, this is a great step forward for xemu's renderer compatibility.

[abaire]

Just glancing through; a nit in case this bit comes out of draft: assert(false) issues often get reported and go for a long time without being investigated, making it non-trivial to work out what exactly failed. Can we make it a pattern to do assert(!"Some description of why this should never happen") instead? Then it's durable at time of reporting and reduces the need to walk back through blame to try to puzzle out why the assert existed.

[mborgerson]

Agreed--In new code this is being done, but there is still plenty of this pattern scattered throughout existing code. This line is removed anyway.