Try to generate a GP3 stroke using modifier.

It's not effective anyway

@@ -1129,12 +1129,12 @@ static int add_material_from_template(Main &bmain, Object &ob, const ColorTempla
   return index;
 }
 
-static bke::CurvesGeometry create_drawing_data(const Span<float3> positions,

@@ -200,6 +200,13 @@ IndexMask retrieve_editable_and_selected_elements(Object &object,
                                                   bke::AttrDomain selection_domain,
                                                   IndexMaskMemory &memory);
 
+bke::CurvesGeometry create_drawing_data(const Span<float3> positions,

@@ -2486,6 +2487,7 @@ typedef enum VolumeToMeshFlag {
   VOLUME_TO_MESH_USE_SMOOTH_SHADE = 1 << 0,
 } VolumeToMeshFlag;
 
+/* enum is kept in legacy dna. */

@@ -2550,0 +2555,4 @@
+  GreasePencilModifierInfluenceData influence;
+  /** `GreasePencilSubdivModifierFlag`. */
+  int flag;
+  /** Factor of subdivision. */

@@ -0,0 +98,4 @@
+static void deform_stroke(ModifierData *md,
+                          Depsgraph * /*depsgraph*/,
+                          Object *ob,
+                          bke::greasepencil::Drawing *drawing)

@@ -0,0 +102,4 @@
+{
+  GreasePencilSubdivModifierData *mmd = (GreasePencilSubdivModifierData *)md;
+
+  if (mmd->level < 1) {

@@ -0,0 +122,4 @@
+                                bke::GeometrySet *geometry_set)
+{
+  GreasePencilSubdivModifierData *mmd = (GreasePencilSubdivModifierData *)md;
+  GreasePencil *gp = geometry_set->get_grease_pencil_for_write();

@@ -0,0 +123,4 @@
+{
+  GreasePencilSubdivModifierData *mmd = (GreasePencilSubdivModifierData *)md;
+  GreasePencil *gp = geometry_set->get_grease_pencil_for_write();
+  const int frame = DEG_get_evaluated_scene(ctx->depsgraph)->r.cfra;

@@ -0,0 +125,4 @@
+  GreasePencil *gp = geometry_set->get_grease_pencil_for_write();
+  const int frame = DEG_get_evaluated_scene(ctx->depsgraph)->r.cfra;
+
+  if (!gp) {

@@ -0,0 +130,4 @@
+  }
+
+  IndexMaskMemory mask_memory;
+  IndexMask layer_mask = modifier::greasepencil::get_filtered_layer_mask(

@@ -0,0 +174,4 @@
+}
+
+ModifierTypeInfo modifierType_GreasePencilSubdiv = {
+    /*idname*/ "Grese Pencil Subdiv Modifier",

@@ -0,0 +175,4 @@
+
+ModifierTypeInfo modifierType_GreasePencilSubdiv = {
+    /*idname*/ "Grese Pencil Subdiv Modifier",
+    /*name*/ N_("Subdiv Modifier"),

@@ -0,0 +123,4 @@
+    return;
+  }
+
+  GreasePencil *gp = geometry_set->get_grease_pencil_for_write();

@@ -0,0 +55,4 @@
+
+static void init_data(ModifierData *md)
+{
+  GreasePencilSubdivModifierData *gpmd = (GreasePencilSubdivModifierData *)md;

@@ -0,0 +95,4 @@
+  modifier::greasepencil::read_influence_data(reader, &mmd->influence);
+}
+
+static void deform_stroke(ModifierData *md,

@@ -7680,0 +7708,4 @@
+
+  prop = RNA_def_property(srna, "open_influence_panel", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(
+      prop, nullptr, "flag", MOD_GREASE_PENCIL_OPACITY_OPEN_INFLUENCE_PANEL);

@@ -0,0 +8,4 @@
+
+#include "BLI_array.hh"
+#include "BLI_index_mask.hh"
+#include "BLI_math_matrix.h"

@@ -0,0 +97,4 @@
+  modifier::greasepencil::read_influence_data(reader, &mmd->influence);
+}
+
+static void deform_drawing(ModifierData *md,

@@ -0,0 +108,4 @@
+  const IndexMask strokes = modifier::greasepencil::get_filtered_stroke_mask(
+      ob, drawing.strokes_for_write(), mmd->influence, memory);
+
+  VArray<int> cuts = VArray<int>::ForSingle(mmd->level, drawing.strokes().points_num());

@@ -7680,0 +7713,4 @@
+  prop = RNA_def_property(srna, "level", PROP_INT, PROP_NONE);
+  RNA_def_property_int_sdna(prop, nullptr, "level");
+  RNA_def_property_range(prop, 0, 16);
+  RNA_def_property_ui_range(prop, 0.0, 5.0, 1, 0);

@@ -7680,0 +7701,4 @@
+
+  rna_def_modifier_grease_pencil_layer_filter(srna);
+  rna_def_modifier_grease_pencil_material_filter(
+      srna, "rna_GreasePencilOpacityModifier_material_filter_set");

@@ -7680,0 +7715,4 @@
+  prop = RNA_def_property(srna, "level", PROP_INT, PROP_NONE);
+  RNA_def_property_int_sdna(prop, nullptr, "level");
+  RNA_def_property_range(prop, 0, 16);
+  RNA_def_property_ui_range(prop, 0.0, 5.0, 1, 0);

@@ -7680,0 +7717,4 @@
+  /* Since the new subdiv algorithm uses linear cut count, we set the limits as 2^n the old value
+   * to get the same range as before. */
+  RNA_def_property_range(prop, 0, 2 ^ 16);
+  RNA_def_property_ui_range(prop, 0, 2 ^ 5, 1, 0);

@@ -0,0 +174,4 @@
+    /*struct_name*/ "GreasePencilSubdivModifierData",
+    /*struct_size*/ sizeof(GreasePencilSubdivModifierData),
+    /*srna*/ &RNA_GreasePencilSubdivModifier,
+    /*type*/ ModifierTypeType::Nonconstructive,

@@ -0,0 +175,4 @@
+    /*struct_size*/ sizeof(GreasePencilSubdivModifierData),
+    /*srna*/ &RNA_GreasePencilSubdivModifier,
+    /*type*/ ModifierTypeType::Nonconstructive,
+    /*flags*/ eModifierTypeFlag_AcceptsGreasePencil,