source/blender/blenkernel/intern/grease_pencil.cc

@@ -594,7 +594,7 @@ Layer::Layer()
   this->frames_storage.values = nullptr;
   this->frames_storage.flag = 0;
 
-  this->blend_mode = GP_LAYER_BLEND_NONE;
+  // this->blend_mode = GP_LAYER_BLEND_NONE;
   this->opacity = 1.0f;
 
   BLI_listbase_clear(&this->masks);
@@ -615,7 +615,7 @@ Layer::Layer(const Layer &other) : Layer()
 
   /* Note: We do not duplicate the frame storage since it is only needed for writing. */
 
-  this->blend_mode = other.blend_mode;
+  // this->blend_mode = other.blend_mode;
   this->opacity = other.opacity;
 
   this->runtime->frames_ = other.runtime->frames_;

source/blender/draw/engines/gpencil/gpencil_layer.hh

@@ -41,7 +41,7 @@ class LayerModule {
     gp_layer.tint = float4(1.0f, 1.0f, 1.0f, 0.0f);
     gp_layer.stroke_index_offset = 0.0f;
 
-    gp_layer.blend_mode = layer.blend_mode;
+    // gp_layer.blend_mode = layer.blend_mode;
     gp_layer.opacity = layer.opacity;
 
     if (layer.opacity != 1.0f) {

source/blender/editors/grease_pencil/intern/grease_pencil_layers.cc

@@ -11,6 +11,7 @@
 
 #include "DEG_depsgraph.hh"
 
+#include "ED_curves.hh"
 #include "ED_grease_pencil.hh"
 
 #include "RNA_access.hh"
@@ -36,6 +37,17 @@ void select_layer_channel(GreasePencil &grease_pencil, bke::greasepencil::Layer
   }
 }
 
+static int get_active_layer_index(const GreasePencil &grease_pencil)
+{
+  for (const int layer_index : grease_pencil.layers().index_range()) {
+    if (grease_pencil.is_layer_active(grease_pencil.layers()[layer_index])) {
+      return layer_index;
+    }
+  }
+
+  return 0;
+}
+
 static int grease_pencil_layer_add_exec(bContext *C, wmOperator *op)
 {
   using namespace blender::bke::greasepencil;
@@ -60,6 +72,25 @@ static int grease_pencil_layer_add_exec(bContext *C, wmOperator *op)
     grease_pencil.insert_blank_frame(new_layer, scene->r.cfra, 0, BEZT_KEYTYPE_KEYFRAME);
   }
 
+  const int active_index = get_active_layer_index(grease_pencil);
+
+  bke::MutableAttributeAccessor attributes = grease_pencil.attributes_for_write();
+
+  /* Initialize the rest of the attributes with default values. */
+  Set<std::string> attributes_to_skip{{"Name"}};
+  attributes.for_all(
+      [&](const bke::AttributeIDRef &id, const bke::AttributeMetaData /*meta_data*/) {
+        if (attributes_to_skip.contains(id.name())) {
+          return true;
+        }
+        bke::GSpanAttributeWriter attribute = attributes.lookup_for_write_span(id);
+        const CPPType &type = attribute.span.type();
+        GMutableSpan new_data = attribute.span.slice(IndexRange(active_index, 1));
+        type.fill_assign_n(type.default_value(), new_data.data(), new_data.size());
+        attribute.finish();
+        return true;
+      });
+
   MEM_SAFE_FREE(new_layer_name);
 
   DEG_id_tag_update(&grease_pencil.id, ID_RECALC_GEOMETRY);

source/blender/makesrna/intern/rna_grease_pencil.cc

@@ -29,12 +29,15 @@ static const EnumPropertyItem rna_enum_layer_blend_modes_items[] = {
 
 #ifdef RNA_RUNTIME
 
+#  include "BKE_attribute.hh"
 #  include "BKE_grease_pencil.hh"
 
 #  include "BLI_span.hh"
 
 #  include "DEG_depsgraph.hh"
 
+//#  include "WM_api.hh"
+
 static GreasePencil *rna_grease_pencil(const PointerRNA *ptr)
 {
   return reinterpret_cast<GreasePencil *>(ptr->owner_id);
@@ -182,6 +185,48 @@ static int rna_iterator_grease_pencil_layer_groups_length(PointerRNA *ptr)
   return grease_pencil->layer_groups().size();
 }
 
+static int get_active_layer_index(const GreasePencil &grease_pencil)
+{
+  for (const int layer_index : grease_pencil.layers().index_range()) {
+    if (grease_pencil.is_layer_active(grease_pencil.layers()[layer_index])) {
+      return layer_index;
+    }
+  }
+
+  return 0;
+}
+
+static int rna_GreasePencilLayer_blend_mode_get(PointerRNA *ptr)
+{
+  using namespace blender;
+  GreasePencil &grease_pencil = *rna_grease_pencil(ptr);
+
+  const int active_index = get_active_layer_index(grease_pencil);
+
+  bke::MutableAttributeAccessor attributes = grease_pencil.attributes_for_write();
+
+  const VArray<int> blend_mode = *attributes.lookup_or_default<int>(
+      "blend_mode", ATTR_DOMAIN_LAYER, int(GP_LAYER_BLEND_NONE));
+
+  return blend_mode[active_index];
+}
+
+static void rna_GreasePencilLayer_blend_mode_set(PointerRNA *ptr, int value)
+{
+  using namespace blender;
+  GreasePencil &grease_pencil = *rna_grease_pencil(ptr);
+  bke::MutableAttributeAccessor attributes = grease_pencil.attributes_for_write();
+
+  const int active_index = get_active_layer_index(grease_pencil);
+
+  bke::SpanAttributeWriter<int> blend_mode = attributes.lookup_or_add_for_write_span<int>(
+      "blend_mode", ATTR_DOMAIN_LAYER);
+  blend_mode.span[active_index] = value;
+  blend_mode.finish();
+
+  return;
+}
+
 #else
 
 static void rna_def_grease_pencil_layer(BlenderRNA *brna)
@@ -231,8 +276,19 @@ static void rna_def_grease_pencil_layer(BlenderRNA *brna)
   prop = RNA_def_property(srna, "blend_mode", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_sdna(prop, nullptr, "blend_mode");
   RNA_def_property_enum_items(prop, rna_enum_layer_blend_modes_items);
+  RNA_def_property_enum_funcs(prop,
+                              "rna_GreasePencilLayer_blend_mode_get",
+                              "rna_GreasePencilLayer_blend_mode_set",
+                              nullptr);
+  /*
+  RNA_def_property_enum_funcs(prop,
+                              "rna_GreasePencilLayer_blend_mode_get",
+                              "rna_GreasePencilLayer_blend_mode_set",
+                              "rna_GreasePencilLayer_blend_mode_itemf");
+  */
   RNA_def_property_ui_text(prop, "Blend Mode", "Blend mode");
-  
+  RNA_def_property_update(prop, NC_GPENCIL | ND_DATA, "rna_grease_pencil_update");
+
   /* Onion Skinning. */
   prop = RNA_def_property(srna, "use_onion_skinning", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(