Included face area value in tessellation LOD level calculation.

Could probably use some more finetuning in practice, but this is already pretty good.

world.c

@@ -64,59 +64,38 @@ static INLINE short world_pointPlaneDist(const VECTOR *point, const ps1bsp_plane
     return (short)m_pointPlaneDist2(point, &plane->normal, plane->dist);
 }
 
-static INLINE short world_planeDot(const SVECTOR *dir, const ps1bsp_plane_t *plane)
-{
-    // Make use of axis-aligned planes to skip the need for a dot product
-    if (plane->type < 3)
-        return ((short*)dir)[plane->type];
-
-    return (short)m_dot12(dir, &plane->normal);
-}
-
 static INLINE short world_cull_backface(const world_t *world, const ps1bsp_face_t *face)
 {
     // Backface culling using the face's plane and center point
     // This eliminates the need for normal clipping per polygon
-    SVECTOR cam_vec;
-    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;
+    VECTOR cam_vec;
+    cam_vec.vx = (int)face->center.vx - cam_pos.vx;
+    cam_vec.vy = (int)face->center.vy - cam_pos.vy;
+    cam_vec.vz = (int)face->center.vz - cam_pos.vz;
 
     // Check if the face's plane points towards the camera
     const ps1bsp_plane_t *plane = &world->planes[face->planeId];
-    int planeDot = world_planeDot(&cam_vec, plane);
+    int planeDot = m_dot12(&cam_vec, &plane->normal);
     if ((planeDot >= 0) ^ face->side)
         return 0;
- 
-    // Check if the face is behind the camera 
-    // TODO: this may cull faces close to the camera, use VectorNormalS to normalize and check for angles < -60 degrees
-    // TODO: or, just check against all corners of the face...
-    // const ps1bsp_facevertex_t *faceVertices = &world->faceVertices[face->firstFaceVertex];
-    // for (int vertIdx = 0; vertIdx < face->numFaceVertices; ++vertIdx)
-    // {
-    //     const ps1bsp_vertex_t *vert = &world->vertices[faceVertices[vertIdx].index];
-    //     cam_vec.vx = vert->x - cam_pos.vx;
-    //     cam_vec.vy = vert->y - cam_pos.vy;
-    //     cam_vec.vz = vert->z - cam_pos.vz;
-    //     if (m_dot12(cam_vec, cam_dir) >= 0)
-    //         return 0;
-    // }
 
+    // Check if the face is behind the camera
     // NOTE: disabling the behind-the-camera check does *not* actually solve the problem of polygons disappearing when too close to the camera!
     // This means that the GPU probably already clips polygons that stretch too far outside the drawing area. Tessellation should solve this.
     int camDot = m_dot12(&cam_vec, &cam_dir);
     if (camDot < 0)
         return 0;
 
-    int vecLenSqr = m_dot12(&cam_vec, &cam_vec);
-
     // Flip angle for faces that are on the opposite side of their plane
     char flip = 2 * face->side - 1;
     planeDot = planeDot * flip;
 
-    int foo = (planeDot * vecLenSqr) / (camDot  + 1);
-    // TODO: include face area
-    return (short)foo;
+    // Calculate an LOD value for this face, based on camera position & direction, face normal & area and distance.
+    // This is used to determine how many tessellation subdivisions are necessary to prevent texture warping.
+    int vecLenSqr = m_dot12(&cam_vec, &cam_vec);
+    int lod = (planeDot * vecLenSqr) / (camDot  + 1);
+    lod = (lod << 6) / (face->center.pad + 1);
+    return (short)lod;
 }
 
 static u_short world_leafAtPoint(const world_t *world, const VECTOR *point)
@@ -235,19 +214,19 @@ static ps1bsp_face_t *world_sortFaces(const world_t *world, const ps1bsp_leaf_t
 
             face->drawFrame = frameNum;
 
-            // NOTE: this value could be REALLY useful for determining the tessellation subdivisions. It has camera distance *and* angle in it.
-            // Just include the face size/area for an approximate screen size. Maybe also separate x/y/z for angle-dependent tessellation.
-            short dot = world_cull_backface(world, face);
-            if (!dot)
+            // Cull faces that are facing away from the camera
+            // This also returns an LOD value used to determine tessellation level
+            short lod = world_cull_backface(world, face);
+            if (!lod)
                 continue;
 
             face->flags &= ~3;
-            if (dot < 64)
+            if (lod < 64)
                 face->flags |= 1;
-            else if (dot < 128)
+            else if (lod < 128)
                 face->flags |= 2;
-            else if (dot < 256)
-                face->flags |= 3;
+            // else if (lod < 256)
+            //     face->flags |= 3;
 
             // Sort the faces to draw in front-to-back order
             face->nextFace = firstFace;