From 87c5517bddaf369ac6f28cffc38cb08141014e4a Mon Sep 17 00:00:00 2001
From: Nico de Poel <ndepoel@gmail.com>
Date: Fri, 17 Feb 2023 11:42:44 +0100
Subject: [PATCH] Swap texture window only when the twin value changes. Further
 reduces texture window commands, especially when drawing non-tiling faces.
 Also cleans up the drawing code a bit.

---
 draw.h  |  8 ++++++++
 world.c | 27 +++++++++++++--------------
 2 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/draw.h b/draw.h
index 4713b71..ca2a20c 100644
--- a/draw.h
+++ b/draw.h
@@ -51,6 +51,14 @@
 
 static u_int color_white = ((255 << 16) | (255 << 8) | 255);
 
+static INLINE void draw_texwindow(unsigned int texWindow, u_long *ot)
+{
+    DR_TWIN *twin = (DR_TWIN*)mem_prim(sizeof(DR_TWIN));
+    setlen(twin, 1);
+    twin->code[0] = texWindow;
+    addPrim(ot, twin);
+}
+
 static INLINE void draw_triangle_lit(SVECTOR *verts, u_long *ot)
 {
     // Draw a single triangle
diff --git a/world.c b/world.c
index f64db10..cd7fb0f 100644
--- a/world.c
+++ b/world.c
@@ -199,6 +199,9 @@ static void (*world_drawface)(const world_t*, const ps1bsp_face_t*, u_long *ot)
 
 static void world_drawFaces(const world_t *world, const ps1bsp_face_t *firstFace)
 {
+    // Make sure we set the texture window back to default after drawing the world
+    unsigned int prevTexWin = 0xe2000000;
+
     // 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.
     // 2) If we need to stop drawing because the primitive buffer is full, we'll only be culling distant faces.
@@ -208,18 +211,20 @@ static void world_drawFaces(const world_t *world, const ps1bsp_face_t *firstFace
         if (!mem_checkprim(sizeof(POLY_GT4) + sizeof(DR_TWIN), face->totalPrimitives))
             break;
 
-        world_drawface(world, face, curOT);
-
         // Texture window commands needs to be placed *after* the draw commands, because the commands are executed in reverse order
-        if (face->nextFace == NULL || face->textureId != face->nextFace->textureId)
+        // Set the texture window for the previous face if it changes in-between faces
+        const ps1bsp_texture_t *texture = &world->textures[face->textureId];
+        if (prevTexWin != texture->twin)
         {
-            const ps1bsp_texture_t *texture = &world->textures[face->textureId];
-            DR_TWIN *twin = (DR_TWIN*)mem_prim(sizeof(DR_TWIN));
-            setlen(twin, 1);
-            twin->code[0] = texture->twin;
-            addPrim(curOT, twin);
+            draw_texwindow(prevTexWin, curOT);
+            prevTexWin = texture->twin;
         }
+
+        world_drawface(world, face, curOT);
     }
+
+    // Set the texture window for the first face to be drawn
+    draw_texwindow(prevTexWin, curOT);
 }
 
 // Simplified BSP subtree traversal specifically for sorting faces of brush models.
@@ -492,11 +497,5 @@ void world_draw(const world_t *world)
     else
         world_drawface = &world_drawface_lit;
 
-    // Make sure we set the texture window back to default after drawing the world
-    DR_TWIN *twin = (DR_TWIN*)mem_prim(sizeof(DR_TWIN));
-    setlen(twin, 1);
-    twin->code[0] = 0xe2000000;
-    addPrim(curOT, twin);
-
     world_drawFaces(world, firstFace);
 }