BMesh: remove checks for tessellating 2 sided faces

2 sided faces aren't supported and will cause problems in many areas
of Blender's code.

Removing (implied) support for faces with fewer than 3 sides
means the total number of triangles is known ahead of time.

This simplifies adding support for multi-threading and partial updates
to an existing tessellation - as the face and loop indices can be used
to access the range of triangles associated with a face.

Also correct outdated comments.

2 files changed, 11 insertions, 21 deletions

diff --git a/source/blender/bmesh/intern/bmesh_polygon.c b/source/blender/bmesh/intern/bmesh_polygon.c
index 4ae2cc67140..5e6635cc929 100644
--- a/source/blender/bmesh/intern/bmesh_polygon.c
+++ b/source/blender/bmesh/intern/bmesh_polygon.c
@@ -1530,14 +1530,11 @@ void BM_face_as_array_loop_quad(BMFace *f, BMLoop *r_loops[4])
  *
  * \note \a looptris Must be pre-allocated to at least the size of given by: poly_to_tri_count
  */
-void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptris_tot)
+void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3])
 {
-  /* use this to avoid locking pthread for _every_ polygon
-   * and calling the fill function */
+  /* Avoid polygon filling logic for 3-4 sided faces. */
 #define USE_TESSFACE_SPEEDUP
 
-  /* this assumes all faces can be scan-filled, which isn't always true,
-   * worst case we over alloc a little which is acceptable */
 #ifndef NDEBUG
   const int looptris_tot = poly_to_tri_count(bm->totface, bm->totloop);
 #endif
@@ -1549,9 +1546,10 @@ void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptri
   MemArena *arena = NULL;
 
   BM_ITER_MESH (efa, &iter, bm, BM_FACES_OF_MESH) {
+    BLI_assert(efa->len >= 3);
     /* don't consider two-edged faces */
-    if (UNLIKELY(efa->len < 3)) {
-      /* do nothing */
+    if (0) {
+      /* do nothing (needed for else statements below) */
     }
 
 #ifdef USE_TESSFACE_SPEEDUP
@@ -1664,8 +1662,6 @@ void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptri
     arena = NULL;
   }
 
-  *r_looptris_tot = i;
-
   BLI_assert(i <= looptris_tot);
 
 #undef USE_TESSFACE_SPEEDUP
@@ -1674,10 +1670,8 @@ void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptri
 /**
  * A version of #BM_mesh_calc_tessellation that avoids degenerate triangles.
  */
-void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptris_tot)
+void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3])
 {
-  /* this assumes all faces can be scan-filled, which isn't always true,
-   * worst case we over alloc a little which is acceptable */
 #ifndef NDEBUG
   const int looptris_tot = poly_to_tri_count(bm->totface, bm->totloop);
 #endif
@@ -1692,11 +1686,9 @@ void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3], int *r_
   Heap *pf_heap = NULL;
 
   BM_ITER_MESH (efa, &iter, bm, BM_FACES_OF_MESH) {
-    /* don't consider two-edged faces */
-    if (UNLIKELY(efa->len < 3)) {
-      /* do nothing */
-    }
-    else if (efa->len == 3) {
+    BLI_assert(efa->len >= 3);
+
+    if (efa->len == 3) {
       BMLoop *l;
       BMLoop **l_ptr = looptris[i++];
       l_ptr[0] = l = BM_FACE_FIRST_LOOP(efa);
@@ -1805,7 +1797,5 @@ void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3], int *r_
     BLI_heap_free(pf_heap, NULL);
   }
 
-  *r_looptris_tot = i;
-
   BLI_assert(i <= looptris_tot);
 }
diff --git a/source/blender/bmesh/intern/bmesh_polygon.h b/source/blender/bmesh/intern/bmesh_polygon.h
index 8c2b9ee0bff..48837d4d0c6 100644
--- a/source/blender/bmesh/intern/bmesh_polygon.h
+++ b/source/blender/bmesh/intern/bmesh_polygon.h
@@ -24,8 +24,8 @@ struct Heap;
 
 #include "BLI_compiler_attrs.h"
 
-void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptris_tot);
-void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3], int *r_looptris_tot);
+void BM_mesh_calc_tessellation(BMesh *bm, BMLoop *(*looptris)[3]);
+void BM_mesh_calc_tessellation_beauty(BMesh *bm, BMLoop *(*looptris)[3]);
 
 void BM_face_calc_tessellation(const BMFace *f,
                                const bool use_fixed_quad,