GXBegin

• Category: Geometry and Vertex
• Matrix Status: Implemented
• Matrix Notes: SDK parity pass done: typed signature, primitive/vtxfmt guards, and documented max-count handling (nverts==0 -> 65536).
• Matrix Link: Gfx-GX-API-Matrix

Official SDK (Reference)

• Manual page: E:/GPT5/Porpoise_SDK/libPorpoise/reference/man/gfx/gx/Geometry/GXBegin.html
• Related page: E:/GPT5/Porpoise_SDK/libPorpoise/reference/man/gfx/gx/Geometry/GXEnd.html
• SDK source parity check area: E:/GPT5/ACGC-PC-Port-Debug-Stuff/src/static/dolphin/gx
• Notes:
  • Signature/prototype is void GXBegin(GXPrimitive type, GXVtxFmt vtxfmt, u16 nverts).
  • Manual requires vertex stream between GXBegin/GXEnd to match configured descriptors/formats.
  • Manual states the submitted vertex count must match nverts and documents a maximum of 65536 vertices.
  • Manual notes clockwise primitive order is front-facing.

libPorpoise Implementation

• Runtime implementation area: E:/GPT5/Porpoise_SDK/libPorpoise/src/gx/pc_gx.c
• Public API surface: E:/GPT5/Porpoise_SDK/libPorpoise/include/dolphin/gx/GXGeometry.h
• Notes:
  • Runtime signature now matches SDK types (GXPrimitive, GXVtxFmt, u16).
  • Begin-state reset remains intact (current_primitive, current_vtxfmt, vertex counters, default color, current matrix index).
  • PC backend now applies explicit primitive whitelist + vtxfmt bounds guard (fail-soft fallback).
  • nverts==0 is treated as 65536 to match documented max-count semantics for the 16-bit field.

SDK vs Porpoise Diff

• Signature parity:
  • SDK: void GXBegin(GXPrimitive, GXVtxFmt, u16)
  • Porpoise: matches in pc_gx.c and public header
• Behavioral parity:
  • SDK: primitive begin packet with typed primitive/vtxfmt and 16-bit vertex count
  • Porpoise: mirrors begin-state setup and expected-count tracking, with soft guards for invalid input
• Known divergence:
  • SDK uses assert/debug checks for invalid input; PC backend fails soft (fallback to GX_TRIANGLES / GX_VTXFMT0).
  • PC backend auto-flushes previous pending batch when a new GXBegin starts if GXEnd was omitted.

Validation Checklist

• GX demo coverage checked
• Pikmin usage path checked
• Matrix status updated if needed
• Notes updated with concrete file/function references

Working Notes

• Implementation location: GXBegin in E:/GPT5/Porpoise_SDK/libPorpoise/src/gx/pc_gx.c near the vertex-submission section.