Cleanup: simplify sorting during uv packing

Prevent double-sorting during uv packing with bounding-box packing.

Slight speed improvement, slight packing efficiency improvement.

source/blender/blenlib/BLI_boxpack_2d.h

@@ -34,15 +34,17 @@ typedef struct BoxPack {
  * There is no limit to the space boxes may take, only that they will be packed
  * tightly into the lower left hand corner (0,0)
  *
- * \param boxarray: a pre-allocated array of boxes.
+ * \param box_array: a pre-allocated array of boxes.
  *      only the 'box->x' and 'box->y' are set, 'box->w' and 'box->h' are used,
  *      'box->index' is not used at all, the only reason its there
  *          is that the box array is sorted by area and programs need to be able
  *          to have some way of writing the boxes back to the original data.
  * \param len: the number of boxes in the array.
+ * \param sort_boxes: Sort `box_array` before packing.
  * \param r_tot_x, r_tot_y: set so you can normalize the data.
  */
-void BLI_box_pack_2d(BoxPack *boxarray, unsigned int len, float *r_tot_x, float *r_tot_y);
+void BLI_box_pack_2d(
+    BoxPack *box_array, unsigned int len, bool sort_boxes, float *r_tot_x, float *r_tot_y);
 
 typedef struct FixedSizeBoxPack {
   struct FixedSizeBoxPack *next, *prev;

source/blender/blenlib/intern/boxpack_2d.c

@@ -266,7 +266,8 @@ static int vertex_sort(const void *p1, const void *p2, void *vs_ctx_p)
 
 /** \} */
 
-void BLI_box_pack_2d(BoxPack *boxarray, const uint len, float *r_tot_x, float *r_tot_y)
+void BLI_box_pack_2d(
+    BoxPack *boxarray, const uint len, const bool sort_boxes, float *r_tot_x, float *r_tot_y)
 {
   uint box_index, verts_pack_len, i, j, k;
   uint *vertex_pack_indices; /* an array of indices used for sorting verts */
@@ -284,8 +285,11 @@ void BLI_box_pack_2d(BoxPack *boxarray, const uint len, float *r_tot_x, float *r
     return;
   }
 
-  /* Sort boxes, biggest first */
-  qsort(boxarray, (size_t)len, sizeof(BoxPack), box_areasort);
+  if (sort_boxes) {
+    /* Sort boxes, biggest first.
+     * Be careful, qsort is not deterministic! */
+    qsort(boxarray, (size_t)len, sizeof(BoxPack), box_areasort);
+  }
 
   /* Add verts to the boxes, these are only used internally. */
   vert = MEM_mallocN(sizeof(BoxVert[4]) * (size_t)len, "BoxPack Verts");

source/blender/geometry/intern/uv_pack.cc

@@ -821,7 +821,7 @@ static float pack_islands_scale_margin(const Span<PackIsland *> islands,
                          &max_v);
       break;
     default:
-      BLI_box_pack_2d(box_array, int(max_box_pack), &max_u, &max_v);
+      BLI_box_pack_2d(box_array, int(max_box_pack), false, &max_u, &max_v);
       break;
   }
 

source/blender/python/mathutils/mathutils_geometry.c

@@ -1404,8 +1404,9 @@ static PyObject *M_Geometry_box_pack_2d(PyObject *UNUSED(self), PyObject *boxlis
       return NULL; /* exception set */
     }
 
+    const bool sort_boxes = true; /* Caution: BLI_box_pack_2d sorting is non-deterministic. */
     /* Non Python function */
-    BLI_box_pack_2d(boxarray, len, &tot_width, &tot_height);
+    BLI_box_pack_2d(boxarray, len, sort_boxes, &tot_width, &tot_height);
 
     boxPack_ToPyObject(boxlist, boxarray);
     MEM_freeN(boxarray);