scripts/startup/bl_ui/space_userpref.py

@@ -2674,6 +2674,7 @@ class USERPREF_PT_experimental_prototypes(ExperimentalPanel, Panel):
                 ({"property": "use_sculpt_texture_paint"}, ("blender/blender/issues/96225", "#96225")),
                 ({"property": "use_experimental_compositors"}, ("blender/blender/issues/88150", "#88150")),
                 ({"property": "use_grease_pencil_version3"}, ("blender/blender/projects/6", "Grease Pencil 3.0")),
+                ({"property": "use_grease_pencil_version3_convert_on_load"}, ("blender/blender/projects/6", "Grease Pencil 3.0")),
                 ({"property": "use_new_matrix_socket"}, ("blender/blender/issues/116067", "Matrix Socket")),
                 ({"property": "enable_overlay_next"}, ("blender/blender/issues/102179", "#102179")),
                 ({"property": "use_extension_repos"}, ("/blender/blender/issues/117286", "#117286")),

source/blender/blenkernel/BKE_grease_pencil_legacy_convert.hh

@@ -10,6 +10,7 @@
 
 struct bGPdata;
 struct bGPDframe;
+struct BlendFileReadReport;
 struct GreasePencil;
 struct GreasePencilDrawing;
 struct ListBase;
@@ -27,6 +28,9 @@ void legacy_gpencil_to_grease_pencil(Main &bmain, GreasePencil &grease_pencil, b
 
 void legacy_gpencil_object(Main &bmain, Object &object);
 
+/** Main entry point to convert all legacy GPData into GreasePencil data and objects. */
+void legacy_main(Main &bmain, BlendFileReadReport &reports);
+
 void thickness_factor_to_modifier(const bGPdata &src_object_data, Object &dst_object);
 void layer_adjustments_to_modifiers(Main &bmain,
                                     const bGPdata &src_object_data,

source/blender/blenkernel/intern/blendfile_link_append.cc

@@ -36,6 +36,7 @@
 
 #include "BLT_translation.hh"
 
+#include "BKE_grease_pencil_legacy_convert.hh"
 #include "BKE_idtype.hh"
 #include "BKE_key.hh"
 #include "BKE_layer.hh"
@@ -1379,6 +1380,14 @@ void BKE_blendfile_append(BlendfileLinkAppendContext *lapp_context, ReportList *
 
   blendfile_link_append_proxies_convert(bmain, reports);
   BKE_main_mesh_legacy_convert_auto_smooth(*bmain);
+
+  if (U.experimental.use_grease_pencil_version3 &&
+      U.experimental.use_grease_pencil_version3_convert_on_load)
+  {
+    BlendFileReadReport bf_reports{};
+    bf_reports.reports = reports;
+    blender::bke::greasepencil::convert::legacy_main(*bmain, bf_reports);
+  }
 }
 
 void BKE_blendfile_link(BlendfileLinkAppendContext *lapp_context, ReportList *reports)
@@ -1496,6 +1505,14 @@ void BKE_blendfile_link(BlendfileLinkAppendContext *lapp_context, ReportList *re
   if ((lapp_context->params->flag & FILE_LINK) != 0) {
     blendfile_link_append_proxies_convert(lapp_context->params->bmain, reports);
     BKE_main_mesh_legacy_convert_auto_smooth(*lapp_context->params->bmain);
+
+    if (U.experimental.use_grease_pencil_version3 &&
+        U.experimental.use_grease_pencil_version3_convert_on_load)
+    {
+      BlendFileReadReport bf_reports{};
+      bf_reports.reports = reports;
+      blender::bke::greasepencil::convert::legacy_main(*lapp_context->params->bmain, bf_reports);
+    }
   }
 
   BKE_main_namemap_clear(lapp_context->params->bmain);

source/blender/blenkernel/intern/grease_pencil_convert_legacy.cc

@@ -6,6 +6,8 @@
  * \ingroup bke
  */
 
+#include <optional>
+
 #include <fmt/format.h>
 
 #include "BKE_anim_data.hh"
@@ -19,15 +21,20 @@
 #include "BKE_grease_pencil_legacy_convert.hh"
 #include "BKE_idprop.hh"
 #include "BKE_lib_id.hh"
+#include "BKE_lib_remap.hh"
+#include "BKE_main.hh"
 #include "BKE_material.h"
 #include "BKE_modifier.hh"
 #include "BKE_node.hh"
 #include "BKE_node_tree_update.hh"
 #include "BKE_object.hh"
 
+#include "BLO_readfile.hh"
+
 #include "BLI_color.hh"
 #include "BLI_function_ref.hh"
 #include "BLI_listbase.h"
+#include "BLI_map.hh"
 #include "BLI_math_matrix.h"
 #include "BLI_math_vector_types.hh"
 #include "BLI_string.h"
@@ -2024,21 +2031,41 @@ static void legacy_object_modifiers(Main & /*bmain*/, Object &object)
   }
 }
 
-void legacy_gpencil_object(Main &bmain, Object &object)
+static void legacy_gpencil_object_ex(
+    Main &bmain,
+    Object &object,
+    std::optional<blender::Map<bGPdata *, GreasePencil *>> legacy_to_greasepencil_data)
 {
-  bGPdata *gpd = static_cast<bGPdata *>(object.data);
+  BLI_assert((GS(static_cast<ID *>(object.data)->name) == ID_GD_LEGACY));
+
+  bGPdata *gpd = static_cast<bGPdata *>(object.data);
+  GreasePencil *new_grease_pencil = nullptr;
+  bool do_gpencil_data_conversion = true;
+
+  if (legacy_to_greasepencil_data) {
+    new_grease_pencil = legacy_to_greasepencil_data->lookup_default(gpd, nullptr);
+    do_gpencil_data_conversion = (new_grease_pencil == nullptr);
+  }
+
+  if (!new_grease_pencil) {
+    new_grease_pencil = static_cast<GreasePencil *>(
+        BKE_id_new_in_lib(&bmain, gpd->id.lib, ID_GP, gpd->id.name + 2));
+    id_us_min(&new_grease_pencil->id);
+  }
 
-  GreasePencil *new_grease_pencil = static_cast<GreasePencil *>(
-      BKE_id_new(&bmain, ID_GP, gpd->id.name + 2));
   object.data = new_grease_pencil;
   object.type = OB_GREASE_PENCIL;
 
   /* NOTE: Could also use #BKE_id_free_us, to also free the legacy GP if not used anymore? */
   id_us_min(&gpd->id);
-  /* No need to increase user-count of `new_grease_pencil`,
-   * since ID creation already set it to 1. */
+  id_us_plus(&new_grease_pencil->id);
 
-  legacy_gpencil_to_grease_pencil(bmain, *new_grease_pencil, *gpd);
+  if (do_gpencil_data_conversion) {
+    legacy_gpencil_to_grease_pencil(bmain, *new_grease_pencil, *gpd);
+    if (legacy_to_greasepencil_data) {
+      legacy_to_greasepencil_data->add(gpd, new_grease_pencil);
+    }
+  }
 
   legacy_object_modifiers(bmain, object);
 
@@ -2050,6 +2077,45 @@ void legacy_gpencil_object(Main &bmain, Object &object)
   BKE_object_free_derived_caches(&object);
 }
 
+void legacy_gpencil_object(Main &bmain, Object &object)
+{
+  legacy_gpencil_object_ex(bmain, object, std::nullopt);
+}
+
+void legacy_main(Main &bmain, BlendFileReadReport & /*reports*/)
+{
+  /* Allows to convert a legacy GPencil data only once, in case it's used by several objects. */
+  blender::Map<bGPdata *, GreasePencil *> legacy_to_greasepencil_data;
+
+  LISTBASE_FOREACH (Object *, object, &bmain.objects) {
+    if (object->type != OB_GPENCIL_LEGACY) {
+      continue;
+    }
+    legacy_gpencil_object_ex(bmain, *object, std::make_optional(legacy_to_greasepencil_data));
+  }
+
+  /* Potential other usages of legacy bGPdata IDs also need to be remapped to their matching new
+   * GreasePencil counterparts. */
+  blender::bke::id::IDRemapper gpd_remapper;
+  /* Allow remapping from legacy bGPdata IDs to new GreasePencil ones. */
+  gpd_remapper.allow_idtype_mismatch = true;
+
+  LISTBASE_FOREACH (bGPdata *, legacy_gpd, &bmain.gpencils) {
+    GreasePencil *new_grease_pencil = legacy_to_greasepencil_data.lookup_default(legacy_gpd,
+                                                                                 nullptr);
+    if (!new_grease_pencil) {
+      new_grease_pencil = static_cast<GreasePencil *>(
+          BKE_id_new_in_lib(&bmain, legacy_gpd->id.lib, ID_GP, legacy_gpd->id.name + 2));
+      id_us_min(&new_grease_pencil->id);
+      legacy_gpencil_to_grease_pencil(bmain, *new_grease_pencil, *legacy_gpd);
+      legacy_to_greasepencil_data.add(legacy_gpd, new_grease_pencil);
+    }
+    gpd_remapper.add(&legacy_gpd->id, &new_grease_pencil->id);
+  }
+
+  BKE_libblock_remap_multiple(&bmain, gpd_remapper, ID_REMAP_ALLOW_IDTYPE_MISMATCH);
+}
+
 void lineart_wrap_v3(const LineartGpencilModifierData *lmd_legacy,
                      GreasePencilLineartModifierData *lmd)
 {

source/blender/blenloader/intern/versioning_common.cc

@@ -19,6 +19,7 @@
 #include "BLI_string_ref.hh"
 
 #include "BKE_animsys.h"
+#include "BKE_grease_pencil_legacy_convert.hh"
 #include "BKE_idprop.h"
 #include "BKE_ipo.h"
 #include "BKE_lib_id.hh"
@@ -537,4 +538,10 @@ void do_versions_after_setup(Main *new_bmain, BlendFileReadReport *reports)
      * been made idempotent. */
     BKE_main_mesh_legacy_convert_auto_smooth(*new_bmain);
   }
+
+  if (U.experimental.use_grease_pencil_version3 &&
+      U.experimental.use_grease_pencil_version3_convert_on_load)
+  {
+    blender::bke::greasepencil::convert::legacy_main(*new_bmain, *reports);
+  }
 }

source/blender/makesdna/DNA_userdef_types.h

@@ -722,8 +722,9 @@ typedef struct UserDef_Experimental {
   char use_shader_node_previews;
   char use_extension_repos;
   char use_extension_utils;
+  char use_grease_pencil_version3_convert_on_load;
 
-  char _pad[2];
+  char _pad[1];
   /** `makesdna` does not allow empty structs. */
 } UserDef_Experimental;
 

source/blender/makesrna/intern/rna_userdef.cc

@@ -7162,6 +7162,15 @@ static void rna_def_userdef_experimental(BlenderRNA *brna)
   RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
   RNA_def_property_update(prop, 0, "rna_userdef_use_grease_pencil_version3_update");
 
+  prop = RNA_def_property(
+      srna, "use_grease_pencil_version3_convert_on_load", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, nullptr, "use_grease_pencil_version3_convert_on_load", 1);
+  RNA_def_property_ui_text(prop,
+                           "Grease Pencil 3.0 Automatic Conversion",
+                           "Enable automatic conversion to grease pencil 3.0 data when opening a "
+                           "blendfile (only active if 'Grease Pencil 3.0' is enabled)");
+  RNA_def_property_update(prop, 0, "rna_userdef_ui_update");
+
   prop = RNA_def_property(srna, "use_new_matrix_socket", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, nullptr, "use_new_matrix_socket", 1);
   RNA_def_property_ui_text(