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Also correct outdated comments.

source/blender/blenkernel/intern/editmesh.c

@@ -127,9 +127,10 @@ static void editmesh_tessface_calc_intern(BMEditMesh *em)
   }
 
   em->looptris = looptris;
+  em->tottri = looptris_tot;
 
   /* after allocating the em->looptris, we're ready to tessellate */
-  BM_mesh_calc_tessellation(em->bm, em->looptris, &em->tottri);
+  BM_mesh_calc_tessellation(em->bm, em->looptris);
 }
 
 void BKE_editmesh_looptri_calc(BMEditMesh *em)

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);
 }

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,

source/blender/editors/sculpt_paint/paint_mask.c

@@ -1239,10 +1239,9 @@ static void sculpt_gesture_apply_trim(SculptGestureContext *sgcontext)
                      }));
 
   const int looptris_tot = poly_to_tri_count(bm->totface, bm->totloop);
-  int tottri;
   BMLoop *(*looptris)[3];
   looptris = MEM_malloc_arrayN(looptris_tot, sizeof(*looptris), __func__);
-  BM_mesh_calc_tessellation_beauty(bm, looptris, &tottri);
+  BM_mesh_calc_tessellation_beauty(bm, looptris);
 
   BMIter iter;
   int i;
@@ -1290,7 +1289,7 @@ static void sculpt_gesture_apply_trim(SculptGestureContext *sgcontext)
         break;
     }
     BM_mesh_boolean(
-        bm, looptris, tottri, bm_face_isect_pair, NULL, 2, true, true, false, boolean_mode);
+        bm, looptris, looptris_tot, bm_face_isect_pair, NULL, 2, true, true, false, boolean_mode);
   }
 
   MEM_freeN(looptris);

source/blender/modifiers/intern/MOD_boolean.cc

@@ -283,11 +283,10 @@ static void BMD_mesh_intersection(BMesh *bm,
   /* main bmesh intersection setup */
   /* create tessface & intersect */
   const int looptris_tot = poly_to_tri_count(bm->totface, bm->totloop);
-  int tottri;
   BMLoop *(*looptris)[3] = (BMLoop * (*)[3])
       MEM_malloc_arrayN(looptris_tot, sizeof(*looptris), __func__);
 
-  BM_mesh_calc_tessellation_beauty(bm, looptris, &tottri);
+  BM_mesh_calc_tessellation_beauty(bm, looptris);
 
   /* postpone this until after tessellating
    * so we can use the original normals before the vertex are moved */
@@ -364,7 +363,7 @@ static void BMD_mesh_intersection(BMesh *bm,
 
   BM_mesh_intersect(bm,
                     looptris,
-                    tottri,
+                    looptris_tot,
                     bm_face_isect_pair,
                     nullptr,
                     false,

source/blender/python/bmesh/bmesh_py_types.c

@@ -1385,7 +1385,6 @@ static PyObject *bpy_bmesh_calc_loop_triangles(BPy_BMElem *self)
   BMesh *bm;
 
   int looptris_tot;
-  int tottri;
   BMLoop *(*looptris)[3];
 
   PyObject *ret;
@@ -1398,10 +1397,10 @@ static PyObject *bpy_bmesh_calc_loop_triangles(BPy_BMElem *self)
   looptris_tot = poly_to_tri_count(bm->totface, bm->totloop);
   looptris = PyMem_MALLOC(sizeof(*looptris) * looptris_tot);
 
-  BM_mesh_calc_tessellation(bm, looptris, &tottri);
+  BM_mesh_calc_tessellation(bm, looptris);
 
-  ret = PyList_New(tottri);
-  for (i = 0; i < tottri; i++) {
+  ret = PyList_New(looptris_tot);
+  for (i = 0; i < looptris_tot; i++) {
     PyList_SET_ITEM(ret, i, BPy_BMLoop_Array_As_Tuple(bm, looptris[i], 3));
   }
 

source/blender/python/mathutils/mathutils_bvhtree.c

@@ -961,8 +961,6 @@ static PyObject *C_BVHTree_FromBMesh(PyObject *UNUSED(cls), PyObject *args, PyOb
 
   /* Get data for tessellation */
   {
-    int tris_len_dummy;
-
     coords_len = (uint)bm->totvert;
     tris_len = (uint)poly_to_tri_count(bm->totface, bm->totloop);
 
@@ -971,8 +969,7 @@ static PyObject *C_BVHTree_FromBMesh(PyObject *UNUSED(cls), PyObject *args, PyOb
 
     looptris = MEM_mallocN(sizeof(*looptris) * (size_t)tris_len, __func__);
 
-    BM_mesh_calc_tessellation(bm, looptris, &tris_len_dummy);
-    BLI_assert(tris_len_dummy == (int)tris_len);
+    BM_mesh_calc_tessellation(bm, looptris);
   }
 
   {