scripts/startup/bl_ui/space_view3d.py

@@ -765,6 +765,12 @@ class VIEW3D_HT_header(Header):
                     depress=(tool_settings.gpencil_selectmode_edit == 'STROKE'),
                 ).mode = 'STROKE'
 
+
+            if object_mode == 'PAINT_GREASE_PENCIL':
+                row = layout.row()
+                sub = row.row(align=True)
+                sub.prop(tool_settings, "use_gpencil_draw_additive", text="", icon='FREEZE')
+
         # Grease Pencil (legacy)
         if obj and obj.type == 'GPENCIL' and context.gpencil_data:
             gpd = context.gpencil_data

source/blender/blenkernel/BKE_grease_pencil.hh

@@ -310,6 +310,11 @@ class Layer : public ::GreasePencilLayer {
    * drawing. */
   int drawing_index_at(const int frame_number) const;
 
+  /**
+   * \returns the key of the active frame at \a frame_number or -1 if there is no frame.
+   */
+  FramesMapKey frame_key_at(int frame_number) const;
+
   /**
    * \returns a pointer to the active frame at \a frame_number or nullptr if there is no frame.
    */
@@ -329,7 +334,7 @@ class Layer : public ::GreasePencilLayer {
 
  private:
   GreasePencilFrame *add_frame_internal(int frame_number, int drawing_index);
-  FramesMapKey frame_key_at(int frame_number) const;
+
   /**
    * Removes null frames starting from \a begin until \a end (excluded) or until a non-null frame
    * is reached. \param begin, end: Iterators into the `sorted_keys` span. \returns an iterator to

source/blender/blenkernel/intern/grease_pencil.cc

@@ -1382,6 +1382,21 @@ void GreasePencil::add_empty_drawings(const int add_num)
   }
 }
 
+void GreasePencil::add_duplicate_drawings(const int duplicate_num,
+                                          const blender::bke::greasepencil::Drawing &drawing)
+{
+  using namespace blender;
+  BLI_assert(duplicate_num > 0);
+  const int prev_num = this->drawings().size();
+  grow_array<GreasePencilDrawingBase *>(
+      &this->drawing_array, &this->drawing_array_num, duplicate_num);
+  MutableSpan<GreasePencilDrawingBase *> new_drawings = this->drawings().drop_front(prev_num);
+  for (const int i : new_drawings.index_range()) {
+    new_drawings[i] = reinterpret_cast<GreasePencilDrawingBase *>(
+        MEM_new<bke::greasepencil::Drawing>(__func__, drawing));
+  }
+}
+
 bool GreasePencil::insert_blank_frame(blender::bke::greasepencil::Layer &layer,
                                       int frame_number,
                                       int duration,
@@ -1397,6 +1412,73 @@ bool GreasePencil::insert_blank_frame(blender::bke::greasepencil::Layer &layer,
   return true;
 }
 
+static int get_frame_duration(const blender::bke::greasepencil::Layer &layer,
+                              const int frame_number)
+{
+  Span<int> sorted_keys = layer.sorted_keys();
+  const int *frame_number_it = std::lower_bound(
+      sorted_keys.begin(), sorted_keys.end(), frame_number);
+  if (std::next(frame_number_it) == sorted_keys.end()) {
+    return 0;
+  }
+  const int next_frame_number = *(std::next(frame_number_it));
+  return next_frame_number - frame_number;
+}
+
+bool GreasePencil::insert_duplicate_frame(blender::bke::greasepencil::Layer &layer,
+                                          const int src_frame_number,
+                                          const int dst_frame_number,
+                                          const bool do_instance)
+{
+  using namespace blender::bke::greasepencil;
+
+  if (!layer.frames().contains(src_frame_number)) {
+    return false;
+  }
+  const GreasePencilFrame &src_frame = layer.frames().lookup(src_frame_number);
+
+  /* Create the new frame structure, with the same duration.
+   * If we want to make an instance of the source frame, the drawing index gets copied from the
+   * source frame. Otherwise, we set the drawing index to the size of the drawings array, since we
+   * are going to add a new drawing copied from the source drawing. */
+  const int duration = src_frame.is_implicit_hold() ? 0 :
+                                                      get_frame_duration(layer, src_frame_number);
+  const int drawing_index = do_instance ? src_frame.drawing_index : int(this->drawings().size());
+  GreasePencilFrame *dst_frame = layer.add_frame(dst_frame_number, drawing_index, duration);
+
+  if (dst_frame == nullptr) {
+    return false;
+  }
+
+  dst_frame->type = src_frame.type;
+
+  const GreasePencilDrawingBase *src_drawing_base = this->drawings(src_frame.drawing_index);
+  switch (src_drawing_base->type) {
+    case GP_DRAWING: {
+      const Drawing &src_drawing =
+          reinterpret_cast<const GreasePencilDrawing *>(src_drawing_base)->wrap();
+      if (do_instance) {
+        /* Adds the duplicate frame as a new instance of the same drawing. We thus increase the
+         * user count of the corresponding drawing. */
+        src_drawing.add_user();
+      }
+      else {
+        /* Create a copy of the drawing, and add it at the end of the drawings array.
+         * Note that the frame already points to this new drawing, as the drawing index was set to
+         * `int(this->drawings().size())`. */
+        this->add_duplicate_drawings(1, src_drawing);
+      }
+      break;
+    }
+    case GP_DRAWING_REFERENCE:
+      /* TODO: Duplicate drawing references is not yet implemented.
+       * For now, just remove the frame that we inserted. */
+      layer.remove_frame(dst_frame_number);
+      return false;
+  }
+  return true;
+}
+
 void GreasePencil::remove_frame_at(blender::bke::greasepencil::Layer &layer,
                                    const int frame_number)
 {

source/blender/editors/space_action/action_edit.cc

@@ -12,11 +12,14 @@
 #include <cstring>
 
 #include "BLI_blenlib.h"
+#include "BLI_map.hh"
 #include "BLI_math.h"
 #include "BLI_utildefines.h"
 
 #include "BLT_translation.h"
 
+#include "DEG_depsgraph.h"
+
 #include "DNA_anim_types.h"
 #include "DNA_gpencil_legacy_types.h"
 #include "DNA_key_types.h"
@@ -34,6 +37,7 @@
 #include "BKE_fcurve.h"
 #include "BKE_global.h"
 #include "BKE_gpencil_legacy.h"
+#include "BKE_grease_pencil.hh"
 #include "BKE_key.h"
 #include "BKE_nla.h"
 #include "BKE_report.h"
@@ -765,6 +769,45 @@ static void insert_gpencil_key(bAnimContext *ac,
   }
 }
 
+static void insert_grease_pencil_key(bAnimContext *ac,
+                                     bAnimListElem *ale,
+                                     const bool hold_previous)
+{
+  using namespace blender::bke::greasepencil;
+  Layer *layer = static_cast<Layer *>(ale->data);
+  GreasePencil *grease_pencil = reinterpret_cast<GreasePencil *>(ale->id);
+  const int current_frame_number = ac->scene->r.cfra;
+
+  if (layer->frames().contains(current_frame_number)) {
+    return;
+  }
+
+  bool changed = false;
+  if (hold_previous) {
+    const FramesMapKey active_frame_number = layer->frame_key_at(current_frame_number);
+    if ((active_frame_number == -1) || (layer->frames().lookup(active_frame_number).is_null())) {
+      /* There is no active frame to hold to, or it's a null frame. Therefore just insert a blank
+       * frame. */
+      changed = grease_pencil->insert_blank_frame(
+          *layer, current_frame_number, 0, BEZT_KEYTYPE_KEYFRAME);
+    }
+    else {
+      /* Duplicate the active frame. */
+      changed = grease_pencil->insert_duplicate_frame(
+          *layer, active_frame_number, current_frame_number, false);
+    }
+  }
+  else {
+    /* Insert a blank frame. */
+    changed = grease_pencil->insert_blank_frame(
+        *layer, current_frame_number, 0, BEZT_KEYTYPE_KEYFRAME);
+  }
+
+  if (changed) {
+    DEG_id_tag_update(&grease_pencil->id, ID_RECALC_GEOMETRY);
+  }
+}
+
 static void insert_fcurve_key(bAnimContext *ac,
                               bAnimListElem *ale,
                               const AnimationEvalContext anim_eval_context,
@@ -853,6 +896,7 @@ static void insert_action_keys(bAnimContext *ac, short mode)
   else {
     add_frame_mode = GP_GETFRAME_ADD_NEW;
   }
+  const bool grease_pencil_hold_previous = ((ts->gpencil_flags & GP_TOOL_FLAG_RETAIN_LAST) != 0);
 
   /* insert keyframes */
   const AnimationEvalContext anim_eval_context = BKE_animsys_eval_context_construct(
@@ -864,7 +908,7 @@ static void insert_action_keys(bAnimContext *ac, short mode)
         break;
 
       case ANIMTYPE_GREASE_PENCIL_LAYER:
-        /* GPv3: To be implemented. */
+        insert_grease_pencil_key(ac, ale, grease_pencil_hold_previous);
         break;
 
       case ANIMTYPE_FCURVE:

source/blender/makesdna/DNA_grease_pencil_types.h

@@ -481,10 +481,17 @@ typedef struct GreasePencil {
   void remove_layer(blender::bke::greasepencil::Layer &layer);
 
   void add_empty_drawings(int add_num);
+  void add_duplicate_drawings(int duplicate_num,
+                              const blender::bke::greasepencil::Drawing &drawing);
   bool insert_blank_frame(blender::bke::greasepencil::Layer &layer,
                           int frame_number,
                           int duration,
                           eBezTriple_KeyframeType keytype);
+  bool insert_duplicate_frame(blender::bke::greasepencil::Layer &layer,
+                              const int src_frame_number,
+                              const int dst_frame_number,
+                              const bool do_instance);
+
   void remove_frame_at(blender::bke::greasepencil::Layer &layer, int frame_number);
 
   void remove_drawing(int index);