From 04ef63c74270dfe9df458bd8335aac7a7097468a Mon Sep 17 00:00:00 2001
From: Adam Bird <Archez@users.noreply.github.com>
Date: Sat, 10 Jun 2023 11:53:13 -0400
Subject: [PATCH] add gSPExtraGeometryMode macros and command for inverting
 culling (#310)

---
 include/libultraship/libultra/gbi.h | 17 +++++++++++++++++
 src/graphic/Fast3D/gfx_pc.cpp       | 15 +++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/libultraship/libultra/gbi.h b/include/libultraship/libultra/gbi.h
index d47ab96bc..f72898d72 100644
--- a/include/libultraship/libultra/gbi.h
+++ b/include/libultraship/libultra/gbi.h
@@ -183,6 +183,7 @@
 
 // RDP Cmd
 #define G_SETGRAYSCALE 0x39
+#define G_EXTRAGEOMETRYMODE 0x3a
 #define G_SETINTENSITY 0x40
 
 /*
@@ -359,6 +360,11 @@
 #endif
 #endif
 
+/*
+ * G_EXTRAGEOMETRY flags: set extra custom geometry modes
+ */
+#define G_EX_INVERT_CULLING 0x00000001
+
 /* Need these defined for Sprite Microcode */
 #ifdef _LANGUAGE_ASSEMBLY
 #define G_TX_LOADTILE 7
@@ -2653,6 +2659,17 @@ typedef union {
 #define gsSPGrayscale(state) \
     { (_SHIFTL(G_SETGRAYSCALE, 24, 8)), (state) }
 
+#define gSPExtraGeometryMode(pkt, c, s)                                                 \
+    _DW({                                                                               \
+        Gfx* _g = (Gfx*)(pkt);                                                          \
+                                                                                        \
+        _g->words.w0 = _SHIFTL(G_EXTRAGEOMETRYMODE, 24, 8) | _SHIFTL(~(u32)(c), 0, 24); \
+        _g->words.w1 = (u32)(s);                                                        \
+    })
+
+#define gSPSetExtraGeometryMode(pkt, word) gSPExtraGeometryMode((pkt), 0, word)
+#define gSPClearExtraGeometryMode(pkt, word) gSPExtraGeometryMode((pkt), word, 0)
+
 #ifdef F3DEX_GBI_2
 /*
  *  One gSPGeometryMode(pkt,c,s) GBI is equal to these two GBIs.
diff --git a/src/graphic/Fast3D/gfx_pc.cpp b/src/graphic/Fast3D/gfx_pc.cpp
index f00de19d1..ed321fe87 100644
--- a/src/graphic/Fast3D/gfx_pc.cpp
+++ b/src/graphic/Fast3D/gfx_pc.cpp
@@ -116,6 +116,8 @@ static struct RSP {
     uint32_t geometry_mode;
     int16_t fog_mul, fog_offset;
 
+    uint32_t extra_geometry_mode;
+
     struct {
         // U0.16
         uint16_t s, t;
@@ -1382,6 +1384,11 @@ static void gfx_sp_tri1(uint8_t vtx1_idx, uint8_t vtx2_idx, uint8_t vtx3_idx, bo
             cross = -cross;
         }
 
+        // If inverted culling is requested, negate the cross
+        if ((rsp.extra_geometry_mode & G_EX_INVERT_CULLING) == 1) {
+            cross = -cross;
+        }
+
         switch (rsp.geometry_mode & G_CULL_BOTH) {
             case G_CULL_FRONT:
                 if (cross <= 0) {
@@ -1769,6 +1776,11 @@ static void gfx_sp_geometry_mode(uint32_t clear, uint32_t set) {
     rsp.geometry_mode |= set;
 }
 
+static void gfx_sp_extra_geometry_mode(uint32_t clear, uint32_t set) {
+    rsp.extra_geometry_mode &= ~clear;
+    rsp.extra_geometry_mode |= set;
+}
+
 static void gfx_adjust_viewport_or_scissor(XYWidthHeight* area) {
     if (!fbActive) {
         area->width *= RATIO_X;
@@ -3035,6 +3047,9 @@ static void gfx_run_dl(Gfx* cmd) {
                     gfx_s2dex_bg_copy((uObjBg*)cmd->words.w1); // not seg_addr here it seems
                 }
 
+                break;
+            case G_EXTRAGEOMETRYMODE:
+                gfx_sp_extra_geometry_mode(~C0(0, 24), cmd->words.w1);
                 break;
         }
         ++cmd;