From f6dec941b709d4b1a191eddfacda478bdfdc788f Mon Sep 17 00:00:00 2001
From: YimingWu <xp8110@outlook.com>
Date: Tue, 26 Nov 2024 12:11:27 +0100
Subject: [PATCH] Fix #130840: Grease Pencil: Use vgroup count to guard invalid
 defnr

Inside legacy GP -> GPv3 conversion, legacy vertex group `def_nr` was
incorrectly guarded by the group count of each vertex, which can lead to
missing groups since not all vertices will have weights in all groups.
This fix use the total vertex group count to guard invalid `def_nr`
values.

Pull Request: https://projects.blender.org/blender/blender/pulls/130886
---
 .../intern/grease_pencil_convert_legacy.cc         | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/source/blender/blenkernel/intern/grease_pencil_convert_legacy.cc b/source/blender/blenkernel/intern/grease_pencil_convert_legacy.cc
index d31741c1011..3ae643fabfc 100644
--- a/source/blender/blenkernel/intern/grease_pencil_convert_legacy.cc
+++ b/source/blender/blenkernel/intern/grease_pencil_convert_legacy.cc
@@ -637,11 +637,11 @@ class AnimDataConvertor {
  * - Array of indices in the new vertex group list for remapping
  */
 static void find_used_vertex_groups(const bGPDframe &gpf,
-                                    const ListBase &all_names,
+                                    const ListBase &vertex_group_names,
+                                    const int num_vertex_groups,
                                     ListBase &r_vertex_group_names,
                                     Array<int> &r_indices)
 {
-  const int num_vertex_groups = BLI_listbase_count(&all_names);
   Array<int> is_group_used(num_vertex_groups, false);
   LISTBASE_FOREACH (bGPDstroke *, gps, &gpf.strokes) {
     if (!gps->dvert) {
@@ -650,7 +650,7 @@ static void find_used_vertex_groups(const bGPDframe &gpf,
     Span<MDeformVert> dverts = {gps->dvert, gps->totpoints};
     for (const MDeformVert &dvert : dverts) {
       for (const MDeformWeight &weight : Span<MDeformWeight>{dvert.dw, dvert.totweight}) {
-        if (weight.def_nr >= dvert.totweight) {
+        if (weight.def_nr >= num_vertex_groups) {
           /* Ignore invalid deform weight group indices. */
           continue;
         }
@@ -662,7 +662,7 @@ static void find_used_vertex_groups(const bGPDframe &gpf,
   r_indices.reinitialize(num_vertex_groups);
   int new_group_i = 0;
   int old_group_i;
-  LISTBASE_FOREACH_INDEX (const bDeformGroup *, def_group, &all_names, old_group_i) {
+  LISTBASE_FOREACH_INDEX (const bDeformGroup *, def_group, &vertex_group_names, old_group_i) {
     if (!is_group_used[old_group_i]) {
       r_indices[old_group_i] = -1;
       continue;
@@ -842,7 +842,9 @@ static Drawing legacy_gpencil_frame_to_grease_pencil_drawing(const bGPDframe &gp
   /* Find used vertex groups in this drawing. */
   ListBase stroke_vertex_group_names;
   Array<int> stroke_def_nr_map;
-  find_used_vertex_groups(gpf, vertex_group_names, stroke_vertex_group_names, stroke_def_nr_map);
+  const int num_vertex_groups = BLI_listbase_count(&vertex_group_names);
+  find_used_vertex_groups(
+      gpf, vertex_group_names, num_vertex_groups, stroke_vertex_group_names, stroke_def_nr_map);
   BLI_assert(BLI_listbase_is_empty(&curves.vertex_group_names));
   curves.vertex_group_names = stroke_vertex_group_names;
   const bool use_dverts = !BLI_listbase_is_empty(&curves.vertex_group_names);
@@ -853,7 +855,7 @@ static Drawing legacy_gpencil_frame_to_grease_pencil_drawing(const bGPDframe &gp
     dst_dvert.dw = static_cast<MDeformWeight *>(MEM_dupallocN(src_dvert.dw));
     const MutableSpan<MDeformWeight> vertex_weights = {dst_dvert.dw, dst_dvert.totweight};
     for (MDeformWeight &weight : vertex_weights) {
-      if (weight.def_nr >= dst_dvert.totweight) {
+      if (weight.def_nr >= num_vertex_groups) {
         /* Ignore invalid deform weight group indices. */
         continue;
       }