GXSetTexCoordScaleManually

• Category: Texture Coordinate Generation
• Matrix Status: Partial
• Matrix Notes: Verified and implemented manual texcoord scale override state (enable/ss/ts) and shader application before texture lookup; automatic map-size scaling remains approximate on PC backend.
• Matrix Link: Gfx-GX-API-Matrix

Official SDK (Reference)

• Manual page: reference/man/gfx/gx/Texture/GXSetTexCoordScaleManually.html
• SDK source: reference/gx/GXTexture.c (GXSetTexCoordScaleManually)
• SDK behavior:
  • Signature: void GXSetTexCoordScaleManually(GXTexCoordID coord, GXBool enable, u16 ss, u16 ts).
  • Tracks per-texcoord manual-scale enable bits.
  • When enable == GX_TRUE, writes SU scale registers using (ss - 1) / (ts - 1).
  • When enable == GX_FALSE, returns texcoord to automatic scaling path (values retained but ignored).

libPorpoise Implementation

• Public API declaration: include/dolphin/gx/GXTexture.h
• Runtime implementation: src/gx/pc_gx.c (GXSetTexCoordScaleManually)
• Shader path: src/gx/shaders/default.frag
• Internal state: src/gx/pc_gx_internal.h
• Behavior:
  • API signature matches SDK declaration.
  • Validates coord < GX_MAX_TEXCOORD.
  • Flushes in-progress begin batch and marks texgen state dirty.
  • Stores per-texcoord manual enable bit and ss/ts values (0 is clamped to 1 for safe divide path).
  • Fragment shader applies manual scaling as tc /= vec2(ss, ts) before TEV texture lookup when manual mode is enabled for that texcoord.

SDK vs Porpoise Diff

• Signature parity:
  • SDK: void GXSetTexCoordScaleManually(GXTexCoordID, GXBool, u16, u16)
  • Porpoise: same
• Behavioral parity:
  • SDK: per-texcoord manual override over SU auto scaling; disable returns to auto mode.
  • Porpoise: manual override enable/disable and scale values are persisted and honored in shader sampling path.
• Known divergence:
  • Hardware SU register behavior (including exact interaction with automatic map-size scaling and related SU features like cyl-wrap/bias) is approximated on PC backend.
  • Automatic scaling-by-associated-map path is not yet modeled bit-accurately as discrete SU state.

Validation Checklist

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

Working Notes

• This function was previously a stub in pc_gx.c and now has runtime + shader behavior.