From b1e568e5c372be2281202f83637413738270a4d9 Mon Sep 17 00:00:00 2001
From: Nico de Poel <ndepoel@gmail.com>
Date: Sat, 28 Jan 2023 15:47:29 +0100
Subject: [PATCH] Added check to backface culling to see if the face is behind
 the camera. This will be required if we ditch depth-based culling in favor of
 leaf-based depth. Also makes for a nice speed boost in some scenarios
 already.

---
 common.h | 1 +
 input.c  | 4 ++++
 main.c   | 1 +
 world.c  | 6 ++++++
 4 files changed, 12 insertions(+)

diff --git a/common.h b/common.h
index 4daf011..224e89f 100644
--- a/common.h
+++ b/common.h
@@ -22,6 +22,7 @@ typedef struct _STVECTOR {
 
 extern VECTOR cam_pos;
 extern SVECTOR cam_rot;
+extern SVECTOR cam_dir;
 extern u_short cam_leaf;
 
 extern u_short quake_clut;
diff --git a/input.c b/input.c
index d9cb894..7d96d38 100644
--- a/input.c
+++ b/input.c
@@ -34,6 +34,10 @@ void input_process()
 	MATRIX cam_mtx;
 	RotMatrixQ(&cam_rot, &cam_mtx);
 
+	cam_dir.vx = cam_mtx.m[0][1];
+	cam_dir.vy = cam_mtx.m[1][1];
+	cam_dir.vz = cam_mtx.m[2][1];
+
     int deltaTime = time_getDeltaTime();
     int moveInterval = (moveSpeed * deltaTime) >> 12;
     int rotInterval = (moveSpeed * deltaTime) >> 12;
diff --git a/main.c b/main.c
index e773ebc..5b5e49c 100644
--- a/main.c
+++ b/main.c
@@ -11,6 +11,7 @@ extern u_long bsp_test[];
 VECTOR cam_pos = { 2176, 1152, 272 };	// START
 //VECTOR cam_pos = { 1920, -1408, 352 };	// E1M1
 SVECTOR cam_rot = { 0, 0, 0 };
+SVECTOR cam_dir = { 0, ONE, 0 };
 u_short cam_leaf = 0;
 
 world_t world;
diff --git a/world.c b/world.c
index ded0618..d34182b 100644
--- a/world.c
+++ b/world.c
@@ -77,7 +77,13 @@ static INLINE char world_cull_backface(const world_t *world, const ps1bsp_face_t
     cam_vec.vx = face->center.vx - cam_pos.vx;
     cam_vec.vy = face->center.vy - cam_pos.vy;
     cam_vec.vz = face->center.vz - cam_pos.vz;
+
+    // Check if the face is behind the camera
+    short camDot = m_dot12s(cam_vec, cam_dir);
+    if (camDot < 0)
+        return 1;
     
+    // Check if the face's plane points towards the camera
     const ps1bsp_plane_t *plane = &world->planes[face->planeId];
     *dot = world_planeDot(&cam_vec, plane);
     return ((*dot >= 0) ^ face->side);