From ba83d78aa8cbeb9fb1109c8d5e2d8c4d6bc0bd49 Mon Sep 17 00:00:00 2001
From: Nico de Poel <ndepoel@gmail.com>
Date: Mon, 30 Jan 2023 14:08:41 +0100
Subject: [PATCH] Removed the need for global variables for sorting leafs and
 faces

---
 world.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/world.c b/world.c
index c84c627..b24632e 100644
--- a/world.c
+++ b/world.c
@@ -214,10 +214,7 @@ static void world_drawface_textured(const world_t *world, const ps1bsp_face_t *f
 
 static void (*world_drawface)(const world_t*, const ps1bsp_face_t*, u_long *ot) = &world_drawface_fast;
 
-static ps1bsp_leaf_t *firstLeaf = NULL;
-static ps1bsp_face_t *firstFace = NULL;
-
-static void world_drawFaces(const world_t *world)
+static void world_drawFaces(const world_t *world, const ps1bsp_face_t *firstFace)
 {
     // Draw the faces in front-to-back order. There are two advantages to this:
     // 1) We don't need to do any depth calculations. The ordering table will be rendered in reverse order, i.e. back-to-front.
@@ -228,8 +225,9 @@ static void world_drawFaces(const world_t *world)
     }
 }
 
-static void world_sortFaces(const world_t *world)
+static ps1bsp_face_t *world_sortFaces(const world_t *world, const ps1bsp_leaf_t *firstLeaf)
 {
+    ps1bsp_face_t *firstFace = NULL;
     u_long frameNum = time_getFrameNumber();
 
     // Traverse leaves in back-to-front order
@@ -251,9 +249,11 @@ static void world_sortFaces(const world_t *world)
             firstFace = face;
         }
     }
+
+    return firstFace;
 }
 
-static void world_sortLeafs(const world_t *world, short nodeIdx, u_char *pvs)
+static void world_sortLeafs(const world_t *world, short nodeIdx, u_char *pvs, ps1bsp_leaf_t **firstLeaf)
 {
     if (nodeIdx < 0)    // Leaf node
     {
@@ -269,8 +269,8 @@ static void world_sortLeafs(const world_t *world, short nodeIdx, u_char *pvs)
         // Add the leaf to the sorted linked list
         // Since we're traversing the BSP tree front-to-back, adding each leaf at the start sorts the list in back-to-front order
         ps1bsp_leaf_t *leaf = (ps1bsp_leaf_t*)&world->leaves[leafIdx];
-        leaf->nextLeaf = firstLeaf;
-        firstLeaf = leaf;
+        leaf->nextLeaf = *firstLeaf;
+        *firstLeaf = leaf;
         return;
     }
 
@@ -282,10 +282,10 @@ static void world_sortLeafs(const world_t *world, short nodeIdx, u_char *pvs)
     const ps1bsp_plane_t *plane = &world->planes[node->planeId];
     short dist = world_pointPlaneDist(&cam_pos, plane);
     
-    // Sort leafs in front-to-back order, so that we can draw their faces at the correct depths
+    // Traverse the BSP tree in front-to-back order
     char order = dist < 0;
-    world_sortLeafs(world, node->children[order], pvs);
-    world_sortLeafs(world, node->children[order ^ 1], pvs);
+    world_sortLeafs(world, node->children[order], pvs, firstLeaf);
+    world_sortLeafs(world, node->children[order ^ 1], pvs, firstLeaf);
 }
 
 // Decompress PVS data for the given leaf ID and store it in RAM at the given buffer pointer location.
@@ -366,10 +366,8 @@ void world_draw(const world_t *world)
     else
         world_drawface = &world_drawface_lit;
 
-    firstLeaf = NULL;
-    firstFace = NULL;
-
-    world_sortLeafs(world, 0, pvs);
-    world_sortFaces(world);
-    world_drawFaces(world);
+    ps1bsp_leaf_t *firstLeaf = NULL;
+    world_sortLeafs(world, 0, pvs, &firstLeaf);
+    ps1bsp_face_t *firstFace = world_sortFaces(world, firstLeaf);
+    world_drawFaces(world, firstFace);
 }