GPv3: Snap selected grease pencil frames

Update of the ACTION_OT_snap to take into account grease pencil frames.
Implemented modes are snap to current frame, nearest second, and nearest marker.

Pull Request: https://projects.blender.org/blender/blender/pulls/111507

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

@@ -38,6 +38,52 @@ void set_selected_frames_type(bke::greasepencil::Layer &layer,
   }
 }
 
+static float get_snapped_frame_number(const float frame_number,
+                                      Scene &scene,
+                                      const eEditKeyframes_Snap mode)
+{
+  switch (mode) {
+    case SNAP_KEYS_CURFRAME: /* Snap to current frame. */
+      return scene.r.cfra;
+    case SNAP_KEYS_NEARSEC: /* Snap to nearest second. */
+    {
+      float secf = (scene.r.frs_sec / scene.r.frs_sec_base);
+      return floorf(frame_number / secf + 0.5f) * secf;
+    }
+    case SNAP_KEYS_NEARMARKER: /* Snap to nearest marker. */
+      return ED_markers_find_nearest_marker_time(&scene.markers, frame_number);
+    default:
+      break;
+  }
+  return frame_number;
+}
+
+bool snap_selected_frames(GreasePencil &grease_pencil,
+                          bke::greasepencil::Layer &layer,
+                          Scene &scene,
+                          const eEditKeyframes_Snap mode)
+{
+  bool changed = false;
+  blender::Map<int, int> frame_number_destinations;
+  for (auto [frame_number, frame] : layer.frames().items()) {
+    if (!frame.is_selected()) {
+      continue;
+    }
+    const int snapped = round_fl_to_int(
+        get_snapped_frame_number(float(frame_number), scene, mode));
+    if (snapped != frame_number) {
+      frame_number_destinations.add(frame_number, snapped);
+      changed = true;
+    }
+  }
+
+  if (changed) {
+    grease_pencil.move_frames(layer, frame_number_destinations);
+  }
+
+  return changed;
+}
+
 static int get_mirrored_frame_number(const int frame_number,
                                      const Scene &scene,
                                      const eEditKeyframes_Mirror mode,

source/blender/editors/include/ED_grease_pencil.hh

@@ -50,16 +50,21 @@ namespace blender::ed::greasepencil {
 void set_selected_frames_type(bke::greasepencil::Layer &layer,
                               const eBezTriple_KeyframeType key_type);
 
-/* Creates duplicate frames for each selected frame in the layer. The duplicates are stored in the
- * LayerTransformData structure of the layer runtime data. This function also unselects the
- * selected frames, while keeping the duplicates selected. */
-bool duplicate_selected_frames(GreasePencil &grease_pencil, bke::greasepencil::Layer &layer);
+bool snap_selected_frames(GreasePencil &grease_pencil,
+                          bke::greasepencil::Layer &layer,
+                          Scene &scene,
+                          const eEditKeyframes_Snap mode);
 
 bool mirror_selected_frames(GreasePencil &grease_pencil,
                             bke::greasepencil::Layer &layer,
                             Scene &scene,
                             const eEditKeyframes_Mirror mode);
 
+/* Creates duplicate frames for each selected frame in the layer. The duplicates are stored in the
+ * LayerTransformData structure of the layer runtime data. This function also unselects the
+ * selected frames, while keeping the duplicates selected. */
+bool duplicate_selected_frames(GreasePencil &grease_pencil, bke::greasepencil::Layer &layer);
+
 bool remove_all_selected_frames(GreasePencil &grease_pencil, bke::greasepencil::Layer &layer);
 
 void select_layer_channel(GreasePencil &grease_pencil, bke::greasepencil::Layer *layer);

source/blender/editors/space_action/action_edit.cc

@@ -1929,7 +1929,15 @@ static void snap_action_keys(bAnimContext *ac, short mode)
       ED_gpencil_layer_snap_frames(static_cast<bGPDlayer *>(ale->data), ac->scene, mode);
     }
     else if (ale->type == ANIMTYPE_GREASE_PENCIL_LAYER) {
-      /* GPv3: To be implemented. */
+      GreasePencil *grease_pencil = reinterpret_cast<GreasePencil *>(ale->id);
+      GreasePencilLayer *layer = static_cast<GreasePencilLayer *>(ale->data);
+
+      const bool changed = blender::ed::greasepencil::snap_selected_frames(
+          *grease_pencil, layer->wrap(), *(ac->scene), static_cast<eEditKeyframes_Snap>(mode));
+
+      if (changed) {
+        DEG_id_tag_update(&grease_pencil->id, ID_RECALC_GEOMETRY);
+      }
     }
     else if (ale->type == ANIMTYPE_MASKLAYER) {
       ED_masklayer_snap_frames(static_cast<MaskLayer *>(ale->data), ac->scene, mode);