From 25917f0165b5feea6f04c6df21bb0fd2003b1042 Mon Sep 17 00:00:00 2001
From: Hans Goudey <h.goudey@me.com>
Date: Thu, 27 Jul 2023 23:12:45 -0400
Subject: [PATCH] Sculpt: Reduce overhead of PBVH draw with
 blender::FunctionRef

At least on GCC on Linux, it appears std::function has noticeable
overhead compared to blender::FunctionRef. That makes some
sense, as the latter generally handles less, and the performance
difference is mentioned in the function ref header as well.

To test performance, I measured the timing of the first data
upload (`BKE_pbvh_draw_cb`) after entering sculpt mode. For
meshes, I observed a 30% improvement, from 1.7s to 1.3s.
For multires, I observed a change from 290ms to 263ms.
The change should apply to regular draw updates while sculpting,
but that's harder to measure.

This is also cleaner semantically, since the callbacks aren't meant
to own any data, they are just lambdas that capture by reference.
---
 source/blender/draw/intern/draw_pbvh.cc | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/source/blender/draw/intern/draw_pbvh.cc b/source/blender/draw/intern/draw_pbvh.cc
index aa38a05355b..f8b35026631 100644
--- a/source/blender/draw/intern/draw_pbvh.cc
+++ b/source/blender/draw/intern/draw_pbvh.cc
@@ -20,6 +20,7 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_bitmap.h"
+#include "BLI_function_ref.hh"
 #include "BLI_ghash.h"
 #include "BLI_index_range.hh"
 #include "BLI_map.hh"
@@ -58,6 +59,7 @@ using blender::char3;
 using blender::float2;
 using blender::float3;
 using blender::float4;
+using blender::FunctionRef;
 using blender::IndexRange;
 using blender::Map;
 using blender::short3;
@@ -328,7 +330,7 @@ struct PBVHBatches {
   void fill_vbo_normal_faces(
       PBVHVbo & /*vbo*/,
       const PBVH_GPU_Args &args,
-      std::function<void(std::function<void(int, int, int, const int)> callback)> foreach_faces,
+      FunctionRef<void(FunctionRef<void(int, int, int, const int)> callback)> foreach_faces,
       GPUVertBufRaw *access)
   {
     const bool *sharp_faces = static_cast<const bool *>(
@@ -360,9 +362,8 @@ struct PBVHBatches {
   void fill_vbo_grids_intern(
       PBVHVbo &vbo,
       const PBVH_GPU_Args &args,
-      std::function<
-          void(std::function<void(int x, int y, int grid_index, CCGElem *elems[4], int i)> func)>
-          foreach_grids)
+      FunctionRef<void(FunctionRef<void(int x, int y, int grid_index, CCGElem *elems[4], int i)>
+                           func)> foreach_grids)
   {
     uint vert_per_grid = square_i(args.ccg_key.grid_size - 1) * 4;
     uint vert_count = args.grid_indices.size() * vert_per_grid;
@@ -484,7 +485,7 @@ struct PBVHBatches {
     uint totgrid = args.grid_indices.size();
 
     auto foreach_solid =
-        [&](std::function<void(int x, int y, int grid_index, CCGElem *elems[4], int i)> func) {
+        [&](FunctionRef<void(int x, int y, int grid_index, CCGElem *elems[4], int i)> func) {
           for (int i = 0; i < totgrid; i++) {
             const int grid_index = args.grid_indices[i];
 
@@ -509,7 +510,7 @@ struct PBVHBatches {
         };
 
     auto foreach_indexed =
-        [&](std::function<void(int x, int y, int grid_index, CCGElem *elems[4], int i)> func) {
+        [&](FunctionRef<void(int x, int y, int grid_index, CCGElem *elems[4], int i)> func) {
           for (int i = 0; i < totgrid; i++) {
             const int grid_index = args.grid_indices[i];
 
@@ -545,7 +546,7 @@ struct PBVHBatches {
   {
     const blender::Span<int> corner_verts = args.corner_verts;
     auto foreach_faces =
-        [&](std::function<void(int buffer_i, int tri_i, int vertex_i, const int /*looptri_i*/)>
+        [&](FunctionRef<void(int buffer_i, int tri_i, int vertex_i, const int /*looptri_i*/)>
                 func) {
           int buffer_i = 0;
 
@@ -748,7 +749,7 @@ struct PBVHBatches {
 
   void fill_vbo_bmesh(PBVHVbo &vbo, const PBVH_GPU_Args &args)
   {
-    auto foreach_bmesh = [&](std::function<void(BMLoop * l)> callback) {
+    auto foreach_bmesh = [&](FunctionRef<void(BMLoop * l)> callback) {
       GSET_FOREACH_BEGIN (BMFace *, f, args.bm_faces) {
         if (BM_elem_flag_test(f, BM_ELEM_HIDDEN)) {
           continue;