Docs: add additional notes on tessellation, update comments

2 files changed, 43 insertions, 39 deletions

diff --git a/source/blender/blenkernel/intern/mesh_tessellate.c b/source/blender/blenkernel/intern/mesh_tessellate.c
index 0cd1b211e4d..797db4df97f 100644
--- a/source/blender/blenkernel/intern/mesh_tessellate.c
+++ b/source/blender/blenkernel/intern/mesh_tessellate.c
@@ -49,6 +49,8 @@
 
 /* -------------------------------------------------------------------- */
 /** \name MFace Tessellation
+ *
+ * #MFace is a legacy data-structure that should be avoided, use #MLoopTri instead.
  * \{ */
 
 /**
@@ -67,11 +69,10 @@ void BKE_mesh_loops_to_tessdata(CustomData *fdata,
                                 uint (*loopindices)[4],
                                 const int num_faces)
 {
-  /* Note: performances are sub-optimal when we get a NULL mface,
-   *       we could be ~25% quicker with dedicated code...
-   *       Issue is, unless having two different functions with nearly the same code,
-   *       there's not much ways to solve this. Better imho to live with it for now. :/ --mont29
-   */
+  /* NOTE(mont29): performances are sub-optimal when we get a NULL #MFace,
+   * we could be ~25% quicker with dedicated code.
+   * The issue is, unless having two different functions with nearly the same code,
+   * there's not much ways to solve this. Better IMHO to live with it for now (sigh). */
   const int numUV = CustomData_number_of_layers(ldata, CD_MLOOPUV);
   const int numCol = CustomData_number_of_layers(ldata, CD_MLOOPCOL);
   const bool hasPCol = CustomData_has_layer(ldata, CD_PREVIEW_MLOOPCOL);
@@ -139,7 +140,7 @@ void BKE_mesh_loops_to_tessdata(CustomData *fdata,
   }
 
   if (hasLoopTangent) {
-    /* need to do for all uv maps at some point */
+    /* Need to do for all UV maps at some point. */
     float(*ftangents)[4] = CustomData_get_layer(fdata, CD_TANGENT);
     float(*ltangents)[4] = CustomData_get_layer(ldata, CD_TANGENT);
 
@@ -154,12 +155,15 @@ void BKE_mesh_loops_to_tessdata(CustomData *fdata,
 }
 
 /**
- * Recreate tessellation.
+ * Recreate #MFace Tessellation.
  *
  * \param do_face_nor_copy: Controls whether the normals from the poly
  * are copied to the tessellated faces.
  *
  * \return number of tessellation faces.
+ *
+ * \note This doesn't use multi-threading like #BKE_mesh_recalc_looptri since
+ * it's not used in many places and #MFace should be phased out.
  */
 int BKE_mesh_tessface_calc_ex(CustomData *fdata,
                               CustomData *ldata,
@@ -170,13 +174,10 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
                               int totpoly,
                               const bool do_face_nor_copy)
 {
-  /* use this to avoid locking pthread for _every_ polygon
-   * and calling the fill function */
-
 #define USE_TESSFACE_SPEEDUP
-#define USE_TESSFACE_QUADS /* NEEDS FURTHER TESTING */
+#define USE_TESSFACE_QUADS
 
-/* We abuse MFace->edcode to tag quad faces. See below for details. */
+/* We abuse #MFace.edcode to tag quad faces. See below for details. */
 #define TESSFACE_IS_QUAD 1
 
   const int looptri_num = poly_to_tri_count(totpoly, totloop);
@@ -193,9 +194,9 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
   mpoly = CustomData_get_layer(pdata, CD_MPOLY);
   mloop = CustomData_get_layer(ldata, CD_MLOOP);
 
-  /* allocate the length of totfaces, avoid many small reallocs,
-   * if all faces are tri's it will be correct, quads == 2x allocs */
-  /* take care. we are _not_ calloc'ing so be sure to initialize each field */
+  /* Allocate the length of `totfaces`, avoid many small reallocation's,
+   * if all faces are triangles it will be correct, `quads == 2x` allocations. */
+  /* Take care since memory is _not_ zeroed so be sure to initialize each field. */
   mface_to_poly_map = MEM_malloc_arrayN((size_t)looptri_num, sizeof(*mface_to_poly_map), __func__);
   mface = MEM_malloc_arrayN((size_t)looptri_num, sizeof(*mface), __func__);
   lindices = MEM_malloc_arrayN((size_t)looptri_num, sizeof(*lindices), __func__);
@@ -208,7 +209,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
     uint l1, l2, l3, l4;
     uint *lidx;
     if (mp_totloop < 3) {
-      /* do nothing */
+      /* Do nothing. */
     }
 
 #ifdef USE_TESSFACE_SPEEDUP
@@ -217,7 +218,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
     mface_to_poly_map[mface_index] = poly_index; \
     mf = &mface[mface_index]; \
     lidx = lindices[mface_index]; \
-    /* set loop indices, transformed to vert indices later */ \
+    /* Set loop indices, transformed to vert indices later. */ \
     l1 = mp_loopstart + i1; \
     l2 = mp_loopstart + i2; \
     l3 = mp_loopstart + i3; \
@@ -239,7 +240,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
     mface_to_poly_map[mface_index] = poly_index; \
     mf = &mface[mface_index]; \
     lidx = lindices[mface_index]; \
-    /* set loop indices, transformed to vert indices later */ \
+    /* Set loop indices, transformed to vert indices later. */ \
     l1 = mp_loopstart + 0; /* EXCEPTION */ \
     l2 = mp_loopstart + 1; /* EXCEPTION */ \
     l3 = mp_loopstart + 2; /* EXCEPTION */ \
@@ -293,7 +294,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
 
       zero_v3(normal);
 
-      /* calc normal, flipped: to get a positive 2d cross product */
+      /* Calculate the normal, flipped: to get a positive 2D cross product. */
       ml = mloop + mp_loopstart;
       co_prev = mvert[ml[mp_totloop - 1].v].co;
       for (j = 0; j < mp_totloop; j++, ml++) {
@@ -305,7 +306,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
         normal[2] = 1.0f;
       }
 
-      /* project verts to 2d */
+      /* Project verts to 2D. */
       axis_dominant_v3_to_m3_negate(axis_mat, normal);
 
       ml = mloop + mp_loopstart;
@@ -315,7 +316,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
 
       BLI_polyfill_calc_arena(projverts, mp_totloop, 1, tris, arena);
 
-      /* apply fill */
+      /* Apply fill. */
       for (j = 0; j < totfilltri; j++) {
         uint *tri = tris[j];
         lidx = lindices[mface_index];
@@ -323,7 +324,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
         mface_to_poly_map[mface_index] = poly_index;
         mf = &mface[mface_index];
 
-        /* set loop indices, transformed to vert indices later */
+        /* Set loop indices, transformed to vert indices later. */
         l1 = mp_loopstart + tri[0];
         l2 = mp_loopstart + tri[1];
         l3 = mp_loopstart + tri[2];
@@ -359,7 +360,7 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
 
   BLI_assert(totface <= looptri_num);
 
-  /* not essential but without this we store over-alloc'd memory in the CustomData layers */
+  /* Not essential but without this we store over-allocated memory in the #CustomData layers. */
   if (LIKELY(looptri_num != totface)) {
     mface = MEM_reallocN(mface, sizeof(*mface) * (size_t)totface);
     mface_to_poly_map = MEM_reallocN(mface_to_poly_map,
@@ -368,14 +369,14 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
 
   CustomData_add_layer(fdata, CD_MFACE, CD_ASSIGN, mface, totface);
 
-  /* CD_ORIGINDEX will contain an array of indices from tessfaces to the polygons
-   * they are directly tessellated from */
+  /* #CD_ORIGINDEX will contain an array of indices from tessellation-faces to the polygons
+   * they are directly tessellated from. */
   CustomData_add_layer(fdata, CD_ORIGINDEX, CD_ASSIGN, mface_to_poly_map, totface);
   CustomData_from_bmeshpoly(fdata, ldata, totface);
 
   if (do_face_nor_copy) {
     /* If polys have a normals layer, copying that to faces can help
-     * avoid the need to recalculate normals later */
+     * avoid the need to recalculate normals later. */
     if (CustomData_has_layer(pdata, CD_NORMAL)) {
       float(*pnors)[3] = CustomData_get_layer(pdata, CD_NORMAL);
       float(*fnors)[3] = CustomData_add_layer(fdata, CD_NORMAL, CD_CALLOC, NULL, totface);
@@ -387,13 +388,11 @@ int BKE_mesh_tessface_calc_ex(CustomData *fdata,
 
   /* NOTE: quad detection issue - fourth vertidx vs fourth loopidx:
    * Polygons take care of their loops ordering, hence not of their vertices ordering.
-   * Currently, our tfaces' fourth vertex index might be 0 even for a quad. However,
-   * we know our fourth loop index is never 0 for quads (because they are sorted for polygons,
-   * and our quads are still mere copies of their polygons).
-   * So we pass NULL as MFace pointer, and BKE_mesh_loops_to_tessdata
-   * will use the fourth loop index as quad test.
-   * ...
-   */
+   * Currently, our tfaces' fourth vertex index might be 0 even for a quad.
+   * However, we know our fourth loop index is never 0 for quads
+   * (because they are sorted for polygons, and our quads are still mere copies of their polygons).
+   * So we pass NULL as MFace pointer, and #BKE_mesh_loops_to_tessdata
+   * will use the fourth loop index as quad test. */
   BKE_mesh_loops_to_tessdata(fdata, ldata, NULL, mface_to_poly_map, lindices, totface);
 
   /* NOTE: quad detection issue - fourth vertidx vs fourth loopidx:
@@ -431,7 +430,7 @@ void BKE_mesh_tessface_calc(Mesh *mesh)
       mesh->totface,
       mesh->totloop,
       mesh->totpoly,
-      /* calc normals right after, don't copy from polys here */
+      /* Calculate normals right after, don't copy from polys here. */
       false);
 
   BKE_mesh_update_customdata_pointers(mesh, true);
@@ -441,6 +440,8 @@ void BKE_mesh_tessface_calc(Mesh *mesh)
 
 /* -------------------------------------------------------------------- */
 /** \name Loop Tessellation
+ *
+ * Fill in #MLoopTri data-structure.
  * \{ */
 
 /**
diff --git a/source/blender/draw/intern/draw_cache_extract_mesh_render_data.c b/source/blender/draw/intern/draw_cache_extract_mesh_render_data.c
index b0eb0c8bcb3..bccf894cc53 100644
--- a/source/blender/draw/intern/draw_cache_extract_mesh_render_data.c
+++ b/source/blender/draw/intern/draw_cache_extract_mesh_render_data.c
@@ -67,8 +67,8 @@ static void mesh_render_data_loose_geom_load(MeshRenderData *mr, MeshBufferExtra
 static void mesh_render_data_loose_geom_ensure(const MeshRenderData *mr,
                                                MeshBufferExtractionCache *cache)
 {
-  /* Early exit: Are loose geometry already available. Only checking for loose verts as loose edges
-   * and verts are calculated at the same time.*/
+  /* Early exit: Are loose geometry already available.
+   * Only checking for loose verts as loose edges and verts are calculated at the same time. */
   if (cache->loose_geom.verts) {
     return;
   }
@@ -230,7 +230,7 @@ static void mesh_render_data_mat_offset_build(MeshRenderData *mr, MeshBufferExtr
 
 typedef struct MatOffsetUserData {
   MeshRenderData *mr;
-  /* struct is extended during allocation to hold mat_tri_len for each material. */
+  /** This struct is extended during allocation to hold mat_tri_len for each material. */
   int mat_tri_len[0];
 } MatOffsetUserData;
 
@@ -252,7 +252,7 @@ static void mesh_render_data_mat_offset_build_threaded(MeshRenderData *mr,
                                                        int face_len,
                                                        TaskParallelRangeFunc range_func)
 {
-  /* Extending the MatOffsetUserData with an int per material slot. */
+  /* Extending the #MatOffsetUserData with an int per material slot. */
   size_t userdata_size = sizeof(MatOffsetUserData) +
                          (mr->mat_len) * sizeof(*cache->mat_offsets.tri);
   MatOffsetUserData *userdata = MEM_callocN(userdata_size, __func__);
@@ -348,6 +348,9 @@ void mesh_render_data_update_looptris(MeshRenderData *mr,
   if (mr->extract_type != MR_EXTRACT_BMESH) {
     /* Mesh */
     if ((iter_type & MR_ITER_LOOPTRI) || (data_flag & MR_DATA_LOOPTRI)) {
+      /* NOTE(campbell): It's possible to skip allocating tessellation,
+       * the tessellation can be calculated as part of the iterator, see: P2188.
+       * The overall advantage is small (around 1%), so keep this as-is. */
       mr->mlooptri = MEM_mallocN(sizeof(*mr->mlooptri) * mr->tri_len, "MR_DATATYPE_LOOPTRI");
       if (mr->poly_normals != NULL) {
         BKE_mesh_recalc_looptri_with_normals(me->mloop,
@@ -575,7 +578,7 @@ void mesh_render_data_free(MeshRenderData *mr)
   MEM_SAFE_FREE(mr->mlooptri);
   MEM_SAFE_FREE(mr->loop_normals);
 
-  /* Loose geometry are owned by MeshBufferExtractionCache. */
+  /* Loose geometry are owned by #MeshBufferExtractionCache. */
   mr->ledges = NULL;
   mr->lverts = NULL;